Auto merge of #92844 - matthiaskrgr:rollup-z5wb6yi, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #90001 (Make rlib metadata strip works with MIPSr6 architecture)
 - #91687 (rustdoc: do not emit tuple variant fields if none are documented)
 - #91938 (Add `std::error::Report` type)
 - #92006 (Welcome opaque types into the fold)
 - #92142 ([code coverage] Fix missing dead code in modules that are never called)
 - #92277 (rustc_metadata: Stop passing `CrateMetadataRef` by reference (step 1))
 - #92334 (rustdoc: Preserve rendering of macro_rules matchers when possible)
 - #92807 (Update cargo)
 - #92832 (Update RELEASES for 1.58.)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

31 files changed, 1513 insertions, 355 deletions

diff --git a/Cargo.lock b/Cargo.lock
index ef9f91fdb43..ce644f2dbc0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -25,6 +25,17 @@ dependencies = [
 ]
 
 [[package]]
+name = "ahash"
+version = "0.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "43bb833f0bf979d8475d38fbf09ed3b8a55e1885fe93ad3f93239fc6a4f17b98"
+dependencies = [
+ "getrandom 0.2.0",
+ "once_cell",
+ "version_check",
+]
+
+[[package]]
 name = "aho-corasick"
 version = "0.7.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -324,7 +335,7 @@ dependencies = [
  "cargo-test-macro",
  "cargo-test-support",
  "cargo-util",
- "clap",
+ "clap 3.0.6",
  "crates-io",
  "crossbeam-utils 0.8.3",
  "curl",
@@ -604,14 +615,29 @@ dependencies = [
  "ansi_term 0.12.1",
  "atty",
  "bitflags",
- "strsim",
- "textwrap",
+ "strsim 0.8.0",
+ "textwrap 0.11.0",
  "unicode-width",
  "vec_map",
  "yaml-rust 0.3.5",
 ]
 
 [[package]]
+name = "clap"
+version = "3.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1957aa4a5fb388f0a0a73ce7556c5b42025b874e5cdc2c670775e346e97adec0"
+dependencies = [
+ "atty",
+ "bitflags",
+ "indexmap",
+ "os_str_bytes",
+ "strsim 0.10.0",
+ "termcolor",
+ "textwrap 0.14.2",
+]
+
+[[package]]
 name = "clippy"
 version = "0.1.59"
 dependencies = [
@@ -641,7 +667,7 @@ version = "0.0.1"
 dependencies = [
  "bytecount",
  "cargo_metadata 0.14.0",
- "clap",
+ "clap 2.34.0",
  "indoc",
  "itertools 0.10.1",
  "opener",
@@ -1579,6 +1605,7 @@ version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "362385356d610bd1e5a408ddf8d022041774b683f345a1d2cfcb4f60f8ae2db5"
 dependencies = [
+ "ahash",
  "compiler_builtins",
  "rustc-std-workspace-alloc",
  "rustc-std-workspace-core",
@@ -1746,7 +1773,7 @@ name = "installer"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "clap",
+ "clap 2.34.0",
  "flate2",
  "lazy_static",
  "num_cpus",
@@ -2191,7 +2218,7 @@ dependencies = [
  "ammonia",
  "anyhow",
  "chrono",
- "clap",
+ "clap 2.34.0",
  "elasticlunr-rs",
  "env_logger 0.7.1",
  "handlebars",
@@ -2396,8 +2423,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "39f37e50073ccad23b6d09bcb5b263f4e76d3bb6038e4a3c08e52162ffa8abc2"
 dependencies = [
  "compiler_builtins",
- "crc32fast",
- "indexmap",
  "memchr",
  "rustc-std-workspace-alloc",
  "rustc-std-workspace-core",
@@ -2416,6 +2441,18 @@ dependencies = [
 ]
 
 [[package]]
+name = "object"
+version = "0.28.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7ce8b38d41f9f3618fc23f908faae61510f8d8ce2d99cbe910641e8f1971f084"
+dependencies = [
+ "crc32fast",
+ "hashbrown",
+ "indexmap",
+ "memchr",
+]
+
+[[package]]
 name = "odht"
 version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2513,6 +2550,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "os_str_bytes"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e22443d1643a904602595ba1cd8f7d896afe56d26712531c5ff73a15b2fbf64"
+dependencies = [
+ "memchr",
+]
+
+[[package]]
 name = "output_vt100"
 version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2916,7 +2962,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7fec2e85e7a30f8fd31b7cf288ad363b5e51fd2cb6f53b416b0cfaabd84e1ccb"
 dependencies = [
  "bitflags",
- "clap",
+ "clap 2.34.0",
  "derive_more",
  "env_logger 0.7.1",
  "humantime 2.0.1",
@@ -3271,7 +3317,7 @@ dependencies = [
 name = "rustbook"
 version = "0.1.0"
 dependencies = [
- "clap",
+ "clap 2.34.0",
  "env_logger 0.7.1",
  "mdbook",
 ]
@@ -3801,7 +3847,7 @@ dependencies = [
  "itertools 0.9.0",
  "jobserver",
  "libc",
- "object 0.26.2",
+ "object 0.28.1",
  "pathdiff",
  "regex",
  "rustc_apfloat",
@@ -5134,12 +5180,18 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8ea5119cdb4c55b55d432abb513a0429384878c15dde60cc77b1c99de1a95a6a"
 
 [[package]]
+name = "strsim"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
+
+[[package]]
 name = "structopt"
 version = "0.3.25"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "40b9788f4202aa75c240ecc9c15c65185e6a39ccdeb0fd5d008b98825464c87c"
 dependencies = [
- "clap",
+ "clap 2.34.0",
  "lazy_static",
  "structopt-derive",
 ]
@@ -5311,6 +5363,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "textwrap"
+version = "0.14.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0066c8d12af8b5acd21e00547c3797fde4e8677254a7ee429176ccebbe93dd80"
+
+[[package]]
 name = "thiserror"
 version = "1.0.30"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/RELEASES.md b/RELEASES.md
index 01c57ab9170..fc0a5d35f30 100644
--- a/RELEASES.md
+++ b/RELEASES.md
@@ -43,7 +43,6 @@ Stabilized APIs
 - [`Option::unwrap_unchecked`]
 - [`Result::unwrap_unchecked`]
 - [`Result::unwrap_err_unchecked`]
-- [`NonZero{unsigned}::is_power_of_two`]
 - [`File::options`]
 
 These APIs are now usable in const contexts:
@@ -56,10 +55,6 @@ These APIs are now usable in const contexts:
 - [`Duration::checked_mul`]
 - [`Duration::saturating_mul`]
 - [`Duration::checked_div`]
-- [`MaybeUninit::as_ptr`]
-- [`MaybeUninit::as_mut_ptr`]
-- [`MaybeUninit::assume_init`]
-- [`MaybeUninit::assume_init_ref`]
 
 Cargo
 -----
@@ -141,7 +136,6 @@ and related tools.
 [`Option::unwrap_unchecked`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.unwrap_unchecked
 [`Result::unwrap_unchecked`]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.unwrap_unchecked
 [`Result::unwrap_err_unchecked`]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.unwrap_err_unchecked
-[`NonZero{unsigned}::is_power_of_two`]: https://doc.rust-lang.org/stable/std/num/struct.NonZeroU8.html#method.is_power_of_two
 [`File::options`]: https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.options
 [`unix::process::ExitStatusExt::core_dumped`]: https://doc.rust-lang.org/stable/std/os/unix/process/trait.ExitStatusExt.html#tymethod.core_dumped
 [`unix::process::ExitStatusExt::stopped_signal`]: https://doc.rust-lang.org/stable/std/os/unix/process/trait.ExitStatusExt.html#tymethod.stopped_signal
@@ -165,10 +159,6 @@ and related tools.
 [`Duration::div_f32`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.div_f32
 [`Duration::div_duration_f64`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.div_duration_f64
 [`Duration::div_duration_f32`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.div_duration_f32
-[`MaybeUninit::as_ptr`]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_ptr
-[`MaybeUninit::as_mut_ptr`]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_mut_ptr
-[`MaybeUninit::assume_init`]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init
-[`MaybeUninit::assume_init_ref`]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init_ref
 
 Version 1.57.0 (2021-12-02)
 ==========================
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
index e0af5653753..32f18419753 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
@@ -5,12 +5,13 @@ use crate::llvm;
 use llvm::coverageinfo::CounterMappingRegion;
 use rustc_codegen_ssa::coverageinfo::map::{Counter, CounterExpression};
 use rustc_codegen_ssa::traits::{ConstMethods, CoverageInfoMethods};
-use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
-use rustc_hir::def_id::{DefId, DefIdSet};
+use rustc_data_structures::fx::FxIndexSet;
+use rustc_hir::def::DefKind;
+use rustc_hir::def_id::DefIdSet;
 use rustc_llvm::RustString;
+use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::coverage::CodeRegion;
 use rustc_middle::ty::TyCtxt;
-use rustc_span::Symbol;
 
 use std::ffi::CString;
 
@@ -46,7 +47,7 @@ pub fn finalize<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
     // functions exist. Generate synthetic functions with a (required) single counter, and add the
     // MIR `Coverage` code regions to the `function_coverage_map`, before calling
     // `ctx.take_function_coverage_map()`.
-    if !tcx.sess.instrument_coverage_except_unused_functions() {
+    if cx.codegen_unit.is_code_coverage_dead_code_cgu() {
         add_unused_functions(cx);
     }
 
@@ -271,26 +272,35 @@ fn save_function_record(
 /// `DefId`s (`tcx` query `mir_keys`) minus the codegenned `DefId`s (`tcx` query
 /// `codegened_and_inlined_items`).
 ///
-/// *HOWEVER* the codegenned `DefId`s are partitioned across multiple `CodegenUnit`s (CGUs), and
-/// this function is processing a `function_coverage_map` for the functions (`Instance`/`DefId`)
-/// allocated to only one of those CGUs. We must NOT inject any unused functions's `CodeRegion`s
-/// more than once, so we have to pick a CGUs `function_coverage_map` into which the unused
-/// function will be inserted.
+/// These unused functions are then codegen'd in one of the CGUs which is marked as the
+/// "code coverage dead code cgu" during the partitioning process. This prevents us from generating
+/// code regions for the same function more than once which can lead to linker errors regarding
+/// duplicate symbols.
 fn add_unused_functions<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
-    let tcx = cx.tcx;
+    assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
 
-    // FIXME(#79622): Can this solution be simplified and/or improved? Are there other sources
-    // of compiler state data that might help (or better sources that could be exposed, but
-    // aren't yet)?
+    let tcx = cx.tcx;
 
     let ignore_unused_generics = tcx.sess.instrument_coverage_except_unused_generics();
 
-    let all_def_ids: DefIdSet = tcx
+    let eligible_def_ids: DefIdSet = tcx
         .mir_keys(())
         .iter()
         .filter_map(|local_def_id| {
             let def_id = local_def_id.to_def_id();
-            if ignore_unused_generics && tcx.generics_of(def_id).requires_monomorphization(tcx) {
+            let kind = tcx.def_kind(def_id);
+            // `mir_keys` will give us `DefId`s for all kinds of things, not
+            // just "functions", like consts, statics, etc. Filter those out.
+            // If `ignore_unused_generics` was specified, filter out any
+            // generic functions from consideration as well.
+            if !matches!(
+                kind,
+                DefKind::Fn | DefKind::AssocFn | DefKind::Closure | DefKind::Generator
+            ) {
+                return None;
+            } else if ignore_unused_generics
+                && tcx.generics_of(def_id).requires_monomorphization(tcx)
+            {
                 return None;
             }
             Some(local_def_id.to_def_id())
@@ -299,79 +309,17 @@ fn add_unused_functions<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
 
     let codegenned_def_ids = tcx.codegened_and_inlined_items(());
 
-    let mut unused_def_ids_by_file: FxHashMap<Symbol, Vec<DefId>> = FxHashMap::default();
-    for &non_codegenned_def_id in all_def_ids.difference(codegenned_def_ids) {
-        // Make sure the non-codegenned (unused) function has at least one MIR
-        // `Coverage` statement with a code region, and return its file name.
-        if let Some(non_codegenned_file_name) = tcx.covered_file_name(non_codegenned_def_id) {
-            let def_ids =
-                unused_def_ids_by_file.entry(*non_codegenned_file_name).or_insert_with(Vec::new);
-            def_ids.push(non_codegenned_def_id);
-        }
-    }
+    for &non_codegenned_def_id in eligible_def_ids.difference(codegenned_def_ids) {
+        let codegen_fn_attrs = tcx.codegen_fn_attrs(non_codegenned_def_id);
 
-    if unused_def_ids_by_file.is_empty() {
-        // There are no unused functions with file names to add (in any CGU)
-        return;
-    }
-
-    // Each `CodegenUnit` (CGU) has its own function_coverage_map, and generates a specific binary
-    // with its own coverage map.
-    //
-    // Each covered function `Instance` can be included in only one coverage map, produced from a
-    // specific function_coverage_map, from a specific CGU.
-    //
-    // Since unused functions did not generate code, they are not associated with any CGU yet.
-    //
-    // To avoid injecting the unused functions in multiple coverage maps (for multiple CGUs)
-    // determine which function_coverage_map has the responsibility for publishing unreachable
-    // coverage, based on file name: For each unused function, find the CGU that generates the
-    // first function (based on sorted `DefId`) from the same file.
-    //
-    // Add a new `FunctionCoverage` to the `function_coverage_map`, with unreachable code regions
-    // for each region in it's MIR.
-
-    // Convert the `HashSet` of `codegenned_def_ids` to a sortable vector, and sort them.
-    let mut sorted_codegenned_def_ids: Vec<DefId> = codegenned_def_ids.iter().copied().collect();
-    sorted_codegenned_def_ids.sort_unstable();
-
-    let mut first_covered_def_id_by_file: FxHashMap<Symbol, DefId> = FxHashMap::default();
-    for &def_id in sorted_codegenned_def_ids.iter() {
-        if let Some(covered_file_name) = tcx.covered_file_name(def_id) {
-            // Only add files known to have unused functions
-            if unused_def_ids_by_file.contains_key(covered_file_name) {
-                first_covered_def_id_by_file.entry(*covered_file_name).or_insert(def_id);
-            }
+        // If a function is marked `#[no_coverage]`, then skip generating a
+        // dead code stub for it.
+        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NO_COVERAGE) {
+            debug!("skipping unused fn marked #[no_coverage]: {:?}", non_codegenned_def_id);
+            continue;
         }
-    }
-
-    // Get the set of def_ids with coverage regions, known by *this* CoverageContext.
-    let cgu_covered_def_ids: DefIdSet = match cx.coverage_context() {
-        Some(ctx) => ctx
-            .function_coverage_map
-            .borrow()
-            .keys()
-            .map(|&instance| instance.def.def_id())
-            .collect(),
-        None => return,
-    };
 
-    let cgu_covered_files: FxHashSet<Symbol> = first_covered_def_id_by_file
-        .iter()
-        .filter_map(
-            |(&file_name, def_id)| {
-                if cgu_covered_def_ids.contains(def_id) { Some(file_name) } else { None }
-            },
-        )
-        .collect();
-
-    // For each file for which this CGU is responsible for adding unused function coverage,
-    // get the `def_id`s for each unused function (if any), define a synthetic function with a
-    // single LLVM coverage counter, and add the function's coverage `CodeRegion`s. to the
-    // function_coverage_map.
-    for covered_file_name in cgu_covered_files {
-        for def_id in unused_def_ids_by_file.remove(&covered_file_name).into_iter().flatten() {
-            cx.define_unused_fn(def_id);
-        }
+        debug!("generating unused fn: {:?}", non_codegenned_def_id);
+        cx.define_unused_fn(non_codegenned_def_id);
     }
 }
diff --git a/compiler/rustc_codegen_ssa/Cargo.toml b/compiler/rustc_codegen_ssa/Cargo.toml
index 5c13dfdc1b5..6c6ee363ea3 100644
--- a/compiler/rustc_codegen_ssa/Cargo.toml
+++ b/compiler/rustc_codegen_ssa/Cargo.toml
@@ -41,6 +41,6 @@ rustc_target = { path = "../rustc_target" }
 rustc_session = { path = "../rustc_session" }
 
 [dependencies.object]
-version = "0.26.2"
+version = "0.28.0"
 default-features = false
 features = ["read_core", "elf", "macho", "pe", "unaligned", "archive", "write"]
diff --git a/compiler/rustc_codegen_ssa/src/back/metadata.rs b/compiler/rustc_codegen_ssa/src/back/metadata.rs
index 79c24f0f172..6849533abc0 100644
--- a/compiler/rustc_codegen_ssa/src/back/metadata.rs
+++ b/compiler/rustc_codegen_ssa/src/back/metadata.rs
@@ -95,7 +95,7 @@ fn search_for_metadata<'a>(
         .map_err(|e| format!("failed to read {} section in '{}': {}", section, path.display(), e))
 }
 
-fn create_object_file(sess: &Session) -> Option<write::Object> {
+fn create_object_file(sess: &Session) -> Option<write::Object<'static>> {
     let endianness = match sess.target.options.endian {
         Endian::Little => Endianness::Little,
         Endian::Big => Endianness::Big,
@@ -135,12 +135,24 @@ fn create_object_file(sess: &Session) -> Option<write::Object> {
         Architecture::Mips => {
             // copied from `mipsel-linux-gnu-gcc foo.c -c` and
             // inspecting the resulting `e_flags` field.
-            let e_flags = elf::EF_MIPS_ARCH_32R2 | elf::EF_MIPS_CPIC | elf::EF_MIPS_PIC;
+            let e_flags = elf::EF_MIPS_CPIC
+                | elf::EF_MIPS_PIC
+                | if sess.target.options.cpu.contains("r6") {
+                    elf::EF_MIPS_ARCH_32R6 | elf::EF_MIPS_NAN2008
+                } else {
+                    elf::EF_MIPS_ARCH_32R2
+                };
             file.flags = FileFlags::Elf { e_flags };
         }
         Architecture::Mips64 => {
             // copied from `mips64el-linux-gnuabi64-gcc foo.c -c`
-            let e_flags = elf::EF_MIPS_ARCH_64R2 | elf::EF_MIPS_CPIC | elf::EF_MIPS_PIC;
+            let e_flags = elf::EF_MIPS_CPIC
+                | elf::EF_MIPS_PIC
+                | if sess.target.options.cpu.contains("r6") {
+                    elf::EF_MIPS_ARCH_64R6 | elf::EF_MIPS_NAN2008
+                } else {
+                    elf::EF_MIPS_ARCH_64R2
+                };
             file.flags = FileFlags::Elf { e_flags };
         }
         Architecture::Riscv64 if sess.target.options.features.contains("+d") => {
diff --git a/compiler/rustc_infer/src/infer/opaque_types.rs b/compiler/rustc_infer/src/infer/opaque_types.rs
index c2ef0b41e27..d5e65705b28 100644
--- a/compiler/rustc_infer/src/infer/opaque_types.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types.rs
@@ -551,6 +551,22 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
             let predicate = predicate.subst(tcx, substs);
             debug!(?predicate);
 
+            let predicate = predicate.fold_with(&mut BottomUpFolder {
+                tcx,
+                ty_op: |ty| match *ty.kind() {
+                    // Replace all other mentions of the same opaque type with the hidden type,
+                    // as the bounds must hold on the hidden type after all.
+                    ty::Opaque(def_id2, substs2) if def_id == def_id2 && substs == substs2 => {
+                        ty_var
+                    }
+                    // Instantiate nested instances of `impl Trait`.
+                    ty::Opaque(..) => self.instantiate_opaque_types_in_map(ty),
+                    _ => ty,
+                },
+                lt_op: |lt| lt,
+                ct_op: |ct| ct,
+            });
+
             // We can't normalize associated types from `rustc_infer`, but we can eagerly register inference variables for them.
             let predicate = predicate.fold_with(&mut BottomUpFolder {
                 tcx,
@@ -575,10 +591,6 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
                     return tcx.ty_error();
                 }
             }
-            // Change the predicate to refer to the type variable,
-            // which will be the concrete type instead of the opaque type.
-            // This also instantiates nested instances of `impl Trait`.
-            let predicate = self.instantiate_opaque_types_in_map(predicate);
 
             let cause =
                 traits::ObligationCause::new(self.value_span, self.body_id, traits::OpaqueType);
diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 3ec384193c3..85c0d28d5ea 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -218,40 +218,40 @@ impl<'a, 'tcx> Metadata<'a, 'tcx> for (&'a MetadataBlob, &'tcx Session) {
     }
 }
 
-impl<'a, 'tcx> Metadata<'a, 'tcx> for &'a CrateMetadataRef<'a> {
+impl<'a, 'tcx> Metadata<'a, 'tcx> for CrateMetadataRef<'a> {
     #[inline]
     fn blob(self) -> &'a MetadataBlob {
-        &self.blob
+        &self.cdata.blob
     }
     #[inline]
     fn cdata(self) -> Option<CrateMetadataRef<'a>> {
-        Some(*self)
+        Some(self)
     }
 }
 
-impl<'a, 'tcx> Metadata<'a, 'tcx> for (&'a CrateMetadataRef<'a>, &'tcx Session) {
+impl<'a, 'tcx> Metadata<'a, 'tcx> for (CrateMetadataRef<'a>, &'tcx Session) {
     #[inline]
     fn blob(self) -> &'a MetadataBlob {
-        &self.0.blob
+        &self.0.cdata.blob
     }
     #[inline]
     fn cdata(self) -> Option<CrateMetadataRef<'a>> {
-        Some(*self.0)
+        Some(self.0)
     }
     #[inline]
     fn sess(self) -> Option<&'tcx Session> {
-        Some(&self.1)
+        Some(self.1)
     }
 }
 
-impl<'a, 'tcx> Metadata<'a, 'tcx> for (&'a CrateMetadataRef<'a>, TyCtxt<'tcx>) {
+impl<'a, 'tcx> Metadata<'a, 'tcx> for (CrateMetadataRef<'a>, TyCtxt<'tcx>) {
     #[inline]
     fn blob(self) -> &'a MetadataBlob {
-        &self.0.blob
+        &self.0.cdata.blob
     }
     #[inline]
     fn cdata(self) -> Option<CrateMetadataRef<'a>> {
-        Some(*self.0)
+        Some(self.0)
     }
     #[inline]
     fn tcx(self) -> Option<TyCtxt<'tcx>> {
@@ -414,9 +414,9 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for SyntaxContext {
             Ok(cdata
                 .root
                 .syntax_contexts
-                .get(&cdata, id)
+                .get(cdata, id)
                 .unwrap_or_else(|| panic!("Missing SyntaxContext {:?} for crate {:?}", id, cname))
-                .decode((&cdata, sess)))
+                .decode((cdata, sess)))
         })
     }
 }
@@ -442,15 +442,15 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for ExpnId {
             let expn_data = crate_data
                 .root
                 .expn_data
-                .get(&crate_data, index)
+                .get(crate_data, index)
                 .unwrap()
-                .decode((&crate_data, sess));
+                .decode((crate_data, sess));
             let expn_hash = crate_data
                 .root
                 .expn_hashes
-                .get(&crate_data, index)
+                .get(crate_data, index)
                 .unwrap()
-                .decode((&crate_data, sess));
+                .decode((crate_data, sess));
             (expn_data, expn_hash)
         });
         Ok(expn_id)
@@ -706,7 +706,7 @@ impl CrateRoot<'_> {
 }
 
 impl<'a, 'tcx> CrateMetadataRef<'a> {
-    fn raw_proc_macro(&self, id: DefIndex) -> &ProcMacro {
+    fn raw_proc_macro(self, id: DefIndex) -> &'a ProcMacro {
         // DefIndex's in root.proc_macro_data have a one-to-one correspondence
         // with items in 'raw_proc_macros'.
         let pos = self
@@ -721,7 +721,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         &self.raw_proc_macros.unwrap()[pos]
     }
 
-    fn opt_item_ident(&self, item_index: DefIndex, sess: &Session) -> Option<Ident> {
+    fn opt_item_ident(self, item_index: DefIndex, sess: &Session) -> Option<Ident> {
         let name = self.def_key(item_index).disambiguated_data.data.get_opt_name()?;
         let span = match self.root.tables.ident_span.get(self, item_index) {
             Some(lazy_span) => lazy_span.decode((self, sess)),
@@ -737,15 +737,15 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         Some(Ident::new(name, span))
     }
 
-    fn item_ident(&self, item_index: DefIndex, sess: &Session) -> Ident {
+    fn item_ident(self, item_index: DefIndex, sess: &Session) -> Ident {
         self.opt_item_ident(item_index, sess).expect("no encoded ident for item")
     }
 
-    fn maybe_kind(&self, item_id: DefIndex) -> Option<EntryKind> {
+    fn maybe_kind(self, item_id: DefIndex) -> Option<EntryKind> {
         self.root.tables.kind.get(self, item_id).map(|k| k.decode(self))
     }
 
-    fn kind(&self, item_id: DefIndex) -> EntryKind {
+    fn kind(self, item_id: DefIndex) -> EntryKind {
         self.maybe_kind(item_id).unwrap_or_else(|| {
             bug!(
                 "CrateMetadata::kind({:?}): id not found, in crate {:?} with number {}",
@@ -756,7 +756,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         })
     }
 
-    fn def_kind(&self, item_id: DefIndex) -> DefKind {
+    fn def_kind(self, item_id: DefIndex) -> DefKind {
         self.root.tables.def_kind.get(self, item_id).map(|k| k.decode(self)).unwrap_or_else(|| {
             bug!(
                 "CrateMetadata::def_kind({:?}): id not found, in crate {:?} with number {}",
@@ -767,7 +767,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         })
     }
 
-    fn get_span(&self, index: DefIndex, sess: &Session) -> Span {
+    fn get_span(self, index: DefIndex, sess: &Session) -> Span {
         self.root
             .tables
             .span
@@ -776,7 +776,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, sess))
     }
 
-    fn load_proc_macro(&self, id: DefIndex, sess: &Session) -> SyntaxExtension {
+    fn load_proc_macro(self, id: DefIndex, sess: &Session) -> SyntaxExtension {
         let (name, kind, helper_attrs) = match *self.raw_proc_macro(id) {
             ProcMacro::CustomDerive { trait_name, attributes, client } => {
                 let helper_attrs =
@@ -807,7 +807,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         )
     }
 
-    fn get_trait_def(&self, item_id: DefIndex, sess: &Session) -> ty::TraitDef {
+    fn get_trait_def(self, item_id: DefIndex, sess: &Session) -> ty::TraitDef {
         match self.kind(item_id) {
             EntryKind::Trait(data) => {
                 let data = data.decode((self, sess));
@@ -837,7 +837,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_variant(
-        &self,
+        self,
         kind: &EntryKind,
         index: DefIndex,
         parent_did: DefId,
@@ -886,7 +886,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         )
     }
 
-    fn get_adt_def(&self, item_id: DefIndex, tcx: TyCtxt<'tcx>) -> &'tcx ty::AdtDef {
+    fn get_adt_def(self, item_id: DefIndex, tcx: TyCtxt<'tcx>) -> &'tcx ty::AdtDef {
         let kind = self.kind(item_id);
         let did = self.local_def_id(item_id);
 
@@ -914,7 +914,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_explicit_predicates(
-        &self,
+        self,
         item_id: DefIndex,
         tcx: TyCtxt<'tcx>,
     ) -> ty::GenericPredicates<'tcx> {
@@ -922,7 +922,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_inferred_outlives(
-        &self,
+        self,
         item_id: DefIndex,
         tcx: TyCtxt<'tcx>,
     ) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
@@ -935,7 +935,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_super_predicates(
-        &self,
+        self,
         item_id: DefIndex,
         tcx: TyCtxt<'tcx>,
     ) -> ty::GenericPredicates<'tcx> {
@@ -943,7 +943,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_explicit_item_bounds(
-        &self,
+        self,
         item_id: DefIndex,
         tcx: TyCtxt<'tcx>,
     ) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
@@ -955,11 +955,11 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .unwrap_or_default()
     }
 
-    fn get_generics(&self, item_id: DefIndex, sess: &Session) -> ty::Generics {
+    fn get_generics(self, item_id: DefIndex, sess: &Session) -> ty::Generics {
         self.root.tables.generics.get(self, item_id).unwrap().decode((self, sess))
     }
 
-    fn get_type(&self, id: DefIndex, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+    fn get_type(self, id: DefIndex, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
         self.root
             .tables
             .ty
@@ -968,63 +968,63 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, tcx))
     }
 
-    fn get_stability(&self, id: DefIndex) -> Option<attr::Stability> {
+    fn get_stability(self, id: DefIndex) -> Option<attr::Stability> {
         self.root.tables.stability.get(self, id).map(|stab| stab.decode(self))
     }
 
-    fn get_const_stability(&self, id: DefIndex) -> Option<attr::ConstStability> {
+    fn get_const_stability(self, id: DefIndex) -> Option<attr::ConstStability> {
         self.root.tables.const_stability.get(self, id).map(|stab| stab.decode(self))
     }
 
-    fn get_deprecation(&self, id: DefIndex) -> Option<attr::Deprecation> {
+    fn get_deprecation(self, id: DefIndex) -> Option<attr::Deprecation> {
         self.root.tables.deprecation.get(self, id).map(|depr| depr.decode(self))
     }
 
-    fn get_visibility(&self, id: DefIndex) -> ty::Visibility {
+    fn get_visibility(self, id: DefIndex) -> ty::Visibility {
         self.root.tables.visibility.get(self, id).unwrap().decode(self)
     }
 
-    fn get_impl_data(&self, id: DefIndex) -> ImplData {
+    fn get_impl_data(self, id: DefIndex) -> ImplData {
         match self.kind(id) {
             EntryKind::Impl(data) => data.decode(self),
             _ => bug!(),
         }
     }
 
-    fn get_parent_impl(&self, id: DefIndex) -> Option<DefId> {
+    fn get_parent_impl(self, id: DefIndex) -> Option<DefId> {
         self.get_impl_data(id).parent_impl
     }
 
-    fn get_impl_polarity(&self, id: DefIndex) -> ty::ImplPolarity {
+    fn get_impl_polarity(self, id: DefIndex) -> ty::ImplPolarity {
         self.get_impl_data(id).polarity
     }
 
-    fn get_impl_defaultness(&self, id: DefIndex) -> hir::Defaultness {
+    fn get_impl_defaultness(self, id: DefIndex) -> hir::Defaultness {
         self.get_impl_data(id).defaultness
     }
 
-    fn get_impl_constness(&self, id: DefIndex) -> hir::Constness {
+    fn get_impl_constness(self, id: DefIndex) -> hir::Constness {
         self.get_impl_data(id).constness
     }
 
-    fn get_trait_item_def_id(&self, id: DefIndex) -> Option<DefId> {
+    fn get_trait_item_def_id(self, id: DefIndex) -> Option<DefId> {
         self.root.tables.trait_item_def_id.get(self, id).map(|d| d.decode(self))
     }
 
-    fn get_coerce_unsized_info(&self, id: DefIndex) -> Option<ty::adjustment::CoerceUnsizedInfo> {
+    fn get_coerce_unsized_info(self, id: DefIndex) -> Option<ty::adjustment::CoerceUnsizedInfo> {
         self.get_impl_data(id).coerce_unsized_info
     }
 
-    fn get_impl_trait(&self, id: DefIndex, tcx: TyCtxt<'tcx>) -> Option<ty::TraitRef<'tcx>> {
+    fn get_impl_trait(self, id: DefIndex, tcx: TyCtxt<'tcx>) -> Option<ty::TraitRef<'tcx>> {
         self.root.tables.impl_trait_ref.get(self, id).map(|tr| tr.decode((self, tcx)))
     }
 
-    fn get_expn_that_defined(&self, id: DefIndex, sess: &Session) -> ExpnId {
+    fn get_expn_that_defined(self, id: DefIndex, sess: &Session) -> ExpnId {
         self.root.tables.expn_that_defined.get(self, id).unwrap().decode((self, sess))
     }
 
     fn get_const_param_default(
-        &self,
+        self,
         tcx: TyCtxt<'tcx>,
         id: DefIndex,
     ) -> rustc_middle::ty::Const<'tcx> {
@@ -1032,14 +1032,14 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     /// Iterates over all the stability attributes in the given crate.
-    fn get_lib_features(&self, tcx: TyCtxt<'tcx>) -> &'tcx [(Symbol, Option<Symbol>)] {
+    fn get_lib_features(self, tcx: TyCtxt<'tcx>) -> &'tcx [(Symbol, Option<Symbol>)] {
         // FIXME: For a proc macro crate, not sure whether we should return the "host"
         // features or an empty Vec. Both don't cause ICEs.
         tcx.arena.alloc_from_iter(self.root.lib_features.decode(self))
     }
 
     /// Iterates over the language items in the given crate.
-    fn get_lang_items(&self, tcx: TyCtxt<'tcx>) -> &'tcx [(DefId, usize)] {
+    fn get_lang_items(self, tcx: TyCtxt<'tcx>) -> &'tcx [(DefId, usize)] {
         if self.root.is_proc_macro_crate() {
             // Proc macro crates do not export any lang-items to the target.
             &[]
@@ -1054,7 +1054,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     /// Iterates over the diagnostic items in the given crate.
-    fn get_diagnostic_items(&self) -> DiagnosticItems {
+    fn get_diagnostic_items(self) -> DiagnosticItems {
         if self.root.is_proc_macro_crate() {
             // Proc macro crates do not export any diagnostic-items to the target.
             Default::default()
@@ -1079,7 +1079,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     /// Module here is understood in name resolution sense - it can be a `mod` item,
     /// or a crate root, or an enum, or a trait.
     fn for_each_module_child(
-        &self,
+        self,
         id: DefIndex,
         mut callback: impl FnMut(ModChild),
         sess: &Session,
@@ -1177,15 +1177,15 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn is_ctfe_mir_available(&self, id: DefIndex) -> bool {
+    fn is_ctfe_mir_available(self, id: DefIndex) -> bool {
         self.root.tables.mir_for_ctfe.get(self, id).is_some()
     }
 
-    fn is_item_mir_available(&self, id: DefIndex) -> bool {
+    fn is_item_mir_available(self, id: DefIndex) -> bool {
         self.root.tables.mir.get(self, id).is_some()
     }
 
-    fn module_expansion(&self, id: DefIndex, sess: &Session) -> ExpnId {
+    fn module_expansion(self, id: DefIndex, sess: &Session) -> ExpnId {
         match self.kind(id) {
             EntryKind::Mod(_) | EntryKind::Enum(_) | EntryKind::Trait(_) => {
                 self.get_expn_that_defined(id, sess)
@@ -1194,7 +1194,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_optimized_mir(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> Body<'tcx> {
+    fn get_optimized_mir(self, tcx: TyCtxt<'tcx>, id: DefIndex) -> Body<'tcx> {
         self.root
             .tables
             .mir
@@ -1205,7 +1205,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, tcx))
     }
 
-    fn get_mir_for_ctfe(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> Body<'tcx> {
+    fn get_mir_for_ctfe(self, tcx: TyCtxt<'tcx>, id: DefIndex) -> Body<'tcx> {
         self.root
             .tables
             .mir_for_ctfe
@@ -1217,7 +1217,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_thir_abstract_const(
-        &self,
+        self,
         tcx: TyCtxt<'tcx>,
         id: DefIndex,
     ) -> Result<Option<&'tcx [thir::abstract_const::Node<'tcx>]>, ErrorReported> {
@@ -1228,7 +1228,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .map_or(Ok(None), |v| Ok(Some(v.decode((self, tcx)))))
     }
 
-    fn get_unused_generic_params(&self, id: DefIndex) -> FiniteBitSet<u32> {
+    fn get_unused_generic_params(self, id: DefIndex) -> FiniteBitSet<u32> {
         self.root
             .tables
             .unused_generic_params
@@ -1237,7 +1237,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .unwrap_or_default()
     }
 
-    fn get_promoted_mir(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> IndexVec<Promoted, Body<'tcx>> {
+    fn get_promoted_mir(self, tcx: TyCtxt<'tcx>, id: DefIndex) -> IndexVec<Promoted, Body<'tcx>> {
         self.root
             .tables
             .promoted_mir
@@ -1248,7 +1248,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, tcx))
     }
 
-    fn mir_const_qualif(&self, id: DefIndex) -> mir::ConstQualifs {
+    fn mir_const_qualif(self, id: DefIndex) -> mir::ConstQualifs {
         match self.kind(id) {
             EntryKind::AnonConst(qualif, _)
             | EntryKind::Const(qualif, _)
@@ -1263,14 +1263,14 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_fn_has_self_parameter(&self, id: DefIndex) -> bool {
+    fn get_fn_has_self_parameter(self, id: DefIndex) -> bool {
         match self.kind(id) {
             EntryKind::AssocFn(data) => data.decode(self).has_self,
             _ => false,
         }
     }
 
-    fn get_associated_item_def_ids(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> &'tcx [DefId] {
+    fn get_associated_item_def_ids(self, tcx: TyCtxt<'tcx>, id: DefIndex) -> &'tcx [DefId] {
         if let Some(children) = self.root.tables.children.get(self, id) {
             tcx.arena.alloc_from_iter(
                 children.decode((self, tcx.sess)).map(|child_index| self.local_def_id(child_index)),
@@ -1280,7 +1280,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_associated_item(&self, id: DefIndex, sess: &Session) -> ty::AssocItem {
+    fn get_associated_item(self, id: DefIndex, sess: &Session) -> ty::AssocItem {
         let def_key = self.def_key(id);
         let parent = self.local_def_id(def_key.parent.unwrap());
         let ident = self.item_ident(id, sess);
@@ -1307,11 +1307,11 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_item_variances(&'a self, id: DefIndex) -> impl Iterator<Item = ty::Variance> + 'a {
+    fn get_item_variances(self, id: DefIndex) -> impl Iterator<Item = ty::Variance> + 'a {
         self.root.tables.variances.get(self, id).unwrap_or_else(Lazy::empty).decode(self)
     }
 
-    fn get_ctor_def_id_and_kind(&self, node_id: DefIndex) -> Option<(DefId, CtorKind)> {
+    fn get_ctor_def_id_and_kind(self, node_id: DefIndex) -> Option<(DefId, CtorKind)> {
         match self.kind(node_id) {
             EntryKind::Struct(data, _) | EntryKind::Variant(data) => {
                 let vdata = data.decode(self);
@@ -1322,7 +1322,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_item_attrs(
-        &'a self,
+        self,
         id: DefIndex,
         sess: &'a Session,
     ) -> impl Iterator<Item = ast::Attribute> + 'a {
@@ -1346,7 +1346,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, sess))
     }
 
-    fn get_struct_field_names(&self, id: DefIndex, sess: &Session) -> Vec<Spanned<Symbol>> {
+    fn get_struct_field_names(self, id: DefIndex, sess: &Session) -> Vec<Spanned<Symbol>> {
         self.root
             .tables
             .children
@@ -1357,7 +1357,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .collect()
     }
 
-    fn get_struct_field_visibilities(&self, id: DefIndex) -> Vec<Visibility> {
+    fn get_struct_field_visibilities(self, id: DefIndex) -> Vec<Visibility> {
         self.root
             .tables
             .children
@@ -1369,7 +1369,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_inherent_implementations_for_type(
-        &self,
+        self,
         tcx: TyCtxt<'tcx>,
         id: DefIndex,
     ) -> &'tcx [DefId] {
@@ -1384,20 +1384,20 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         )
     }
 
-    fn get_traits(&'a self) -> impl Iterator<Item = DefId> + 'a {
-        self.root.traits.decode(self).map(|index| self.local_def_id(index))
+    fn get_traits(self) -> impl Iterator<Item = DefId> + 'a {
+        self.root.traits.decode(self).map(move |index| self.local_def_id(index))
     }
 
-    fn get_trait_impls(&'a self) -> impl Iterator<Item = (DefId, Option<SimplifiedType>)> + 'a {
-        self.trait_impls.values().flat_map(move |impls| {
+    fn get_trait_impls(self) -> impl Iterator<Item = (DefId, Option<SimplifiedType>)> + 'a {
+        self.cdata.trait_impls.values().flat_map(move |impls| {
             impls
                 .decode(self)
-                .map(|(idx, simplified_self_ty)| (self.local_def_id(idx), simplified_self_ty))
+                .map(move |(idx, simplified_self_ty)| (self.local_def_id(idx), simplified_self_ty))
         })
     }
 
     fn get_implementations_of_trait(
-        &self,
+        self,
         tcx: TyCtxt<'tcx>,
         trait_def_id: DefId,
     ) -> &'tcx [(DefId, Option<SimplifiedType>)] {
@@ -1424,7 +1424,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_trait_of_item(&self, id: DefIndex) -> Option<DefId> {
+    fn get_trait_of_item(self, id: DefIndex) -> Option<DefId> {
         let def_key = self.def_key(id);
         match def_key.disambiguated_data.data {
             DefPathData::TypeNs(..) | DefPathData::ValueNs(..) => (),
@@ -1437,7 +1437,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         })
     }
 
-    fn get_native_libraries(&self, sess: &Session) -> Vec<NativeLib> {
+    fn get_native_libraries(self, sess: &Session) -> Vec<NativeLib> {
         if self.root.is_proc_macro_crate() {
             // Proc macro crates do not have any *target* native libraries.
             vec![]
@@ -1446,7 +1446,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_proc_macro_quoted_span(&self, index: usize, sess: &Session) -> Span {
+    fn get_proc_macro_quoted_span(self, index: usize, sess: &Session) -> Span {
         self.root
             .tables
             .proc_macro_quoted_spans
@@ -1455,7 +1455,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, sess))
     }
 
-    fn get_foreign_modules(&self, tcx: TyCtxt<'tcx>) -> Lrc<FxHashMap<DefId, ForeignModule>> {
+    fn get_foreign_modules(self, tcx: TyCtxt<'tcx>) -> Lrc<FxHashMap<DefId, ForeignModule>> {
         if self.root.is_proc_macro_crate() {
             // Proc macro crates do not have any *target* foreign modules.
             Lrc::new(FxHashMap::default())
@@ -1467,7 +1467,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_dylib_dependency_formats(
-        &self,
+        self,
         tcx: TyCtxt<'tcx>,
     ) -> &'tcx [(CrateNum, LinkagePreference)] {
         tcx.arena.alloc_from_iter(
@@ -1478,7 +1478,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         )
     }
 
-    fn get_missing_lang_items(&self, tcx: TyCtxt<'tcx>) -> &'tcx [lang_items::LangItem] {
+    fn get_missing_lang_items(self, tcx: TyCtxt<'tcx>) -> &'tcx [lang_items::LangItem] {
         if self.root.is_proc_macro_crate() {
             // Proc macro crates do not depend on any target weak lang-items.
             &[]
@@ -1487,7 +1487,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_fn_param_names(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> &'tcx [Ident] {
+    fn get_fn_param_names(self, tcx: TyCtxt<'tcx>, id: DefIndex) -> &'tcx [Ident] {
         let param_names = match self.kind(id) {
             EntryKind::Fn(data) | EntryKind::ForeignFn(data) => data.decode(self).param_names,
             EntryKind::AssocFn(data) => data.decode(self).fn_data.param_names,
@@ -1497,7 +1497,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn exported_symbols(
-        &self,
+        self,
         tcx: TyCtxt<'tcx>,
     ) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportLevel)] {
         if self.root.is_proc_macro_crate() {
@@ -1509,7 +1509,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_rendered_const(&self, id: DefIndex) -> String {
+    fn get_rendered_const(self, id: DefIndex) -> String {
         match self.kind(id) {
             EntryKind::AnonConst(_, data)
             | EntryKind::Const(_, data)
@@ -1518,7 +1518,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn get_macro(&self, id: DefIndex, sess: &Session) -> MacroDef {
+    fn get_macro(self, id: DefIndex, sess: &Session) -> MacroDef {
         match self.kind(id) {
             EntryKind::MacroDef(macro_def) => macro_def.decode((self, sess)),
             _ => bug!(),
@@ -1527,7 +1527,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
 
     // This replicates some of the logic of the crate-local `is_const_fn_raw` query, because we
     // don't serialize constness for tuple variant and tuple struct constructors.
-    fn is_const_fn_raw(&self, id: DefIndex) -> bool {
+    fn is_const_fn_raw(self, id: DefIndex) -> bool {
         let constness = match self.kind(id) {
             EntryKind::AssocFn(data) => data.decode(self).fn_data.constness,
             EntryKind::Fn(data) => data.decode(self).constness,
@@ -1538,7 +1538,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         constness == hir::Constness::Const
     }
 
-    fn asyncness(&self, id: DefIndex) -> hir::IsAsync {
+    fn asyncness(self, id: DefIndex) -> hir::IsAsync {
         match self.kind(id) {
             EntryKind::Fn(data) => data.decode(self).asyncness,
             EntryKind::AssocFn(data) => data.decode(self).fn_data.asyncness,
@@ -1547,7 +1547,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn is_foreign_item(&self, id: DefIndex) -> bool {
+    fn is_foreign_item(self, id: DefIndex) -> bool {
         match self.kind(id) {
             EntryKind::ForeignImmStatic | EntryKind::ForeignMutStatic | EntryKind::ForeignFn(_) => {
                 true
@@ -1556,7 +1556,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn static_mutability(&self, id: DefIndex) -> Option<hir::Mutability> {
+    fn static_mutability(self, id: DefIndex) -> Option<hir::Mutability> {
         match self.kind(id) {
             EntryKind::ImmStatic | EntryKind::ForeignImmStatic => Some(hir::Mutability::Not),
             EntryKind::MutStatic | EntryKind::ForeignMutStatic => Some(hir::Mutability::Mut),
@@ -1564,19 +1564,19 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn generator_kind(&self, id: DefIndex) -> Option<hir::GeneratorKind> {
+    fn generator_kind(self, id: DefIndex) -> Option<hir::GeneratorKind> {
         match self.kind(id) {
             EntryKind::Generator(data) => Some(data),
             _ => None,
         }
     }
 
-    fn fn_sig(&self, id: DefIndex, tcx: TyCtxt<'tcx>) -> ty::PolyFnSig<'tcx> {
+    fn fn_sig(self, id: DefIndex, tcx: TyCtxt<'tcx>) -> ty::PolyFnSig<'tcx> {
         self.root.tables.fn_sig.get(self, id).unwrap().decode((self, tcx))
     }
 
     #[inline]
-    fn def_key(&self, index: DefIndex) -> DefKey {
+    fn def_key(self, index: DefIndex) -> DefKey {
         *self
             .def_key_cache
             .lock()
@@ -1585,13 +1585,13 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     // Returns the path leading to the thing with this `id`.
-    fn def_path(&self, id: DefIndex) -> DefPath {
+    fn def_path(self, id: DefIndex) -> DefPath {
         debug!("def_path(cnum={:?}, id={:?})", self.cnum, id);
         DefPath::make(self.cnum, id, |parent| self.def_key(parent))
     }
 
     fn def_path_hash_unlocked(
-        &self,
+        self,
         index: DefIndex,
         def_path_hashes: &mut FxHashMap<DefIndex, DefPathHash>,
     ) -> DefPathHash {
@@ -1601,17 +1601,17 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     #[inline]
-    fn def_path_hash(&self, index: DefIndex) -> DefPathHash {
+    fn def_path_hash(self, index: DefIndex) -> DefPathHash {
         let mut def_path_hashes = self.def_path_hash_cache.lock();
         self.def_path_hash_unlocked(index, &mut def_path_hashes)
     }
 
     #[inline]
-    fn def_path_hash_to_def_index(&self, hash: DefPathHash) -> DefIndex {
+    fn def_path_hash_to_def_index(self, hash: DefPathHash) -> DefIndex {
         self.def_path_hash_map.def_path_hash_to_def_index(&hash)
     }
 
-    fn expn_hash_to_expn_id(&self, sess: &Session, index_guess: u32, hash: ExpnHash) -> ExpnId {
+    fn expn_hash_to_expn_id(self, sess: &Session, index_guess: u32, hash: ExpnHash) -> ExpnId {
         debug_assert_eq!(ExpnId::from_hash(hash), None);
         let index_guess = ExpnIndex::from_u32(index_guess);
         let old_hash = self.root.expn_hashes.get(self, index_guess).map(|lazy| lazy.decode(self));
@@ -1669,7 +1669,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     ///
     /// Proc macro crates don't currently export spans, so this function does not have
     /// to work for them.
-    fn imported_source_files(&self, sess: &Session) -> &'a [ImportedSourceFile] {
+    fn imported_source_files(self, sess: &Session) -> &'a [ImportedSourceFile] {
         // Translate the virtual `/rustc/$hash` prefix back to a real directory
         // that should hold actual sources, where possible.
         //
diff --git a/compiler/rustc_middle/src/mir/mono.rs b/compiler/rustc_middle/src/mir/mono.rs
index 1422537cd50..3a6c091b331 100644
--- a/compiler/rustc_middle/src/mir/mono.rs
+++ b/compiler/rustc_middle/src/mir/mono.rs
@@ -247,6 +247,9 @@ pub struct CodegenUnit<'tcx> {
     items: FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)>,
     size_estimate: Option<usize>,
     primary: bool,
+    /// True if this is CGU is used to hold code coverage information for dead code,
+    /// false otherwise.
+    is_code_coverage_dead_code_cgu: bool,
 }
 
 /// Specifies the linkage type for a `MonoItem`.
@@ -277,7 +280,13 @@ pub enum Visibility {
 impl<'tcx> CodegenUnit<'tcx> {
     #[inline]
     pub fn new(name: Symbol) -> CodegenUnit<'tcx> {
-        CodegenUnit { name, items: Default::default(), size_estimate: None, primary: false }
+        CodegenUnit {
+            name,
+            items: Default::default(),
+            size_estimate: None,
+            primary: false,
+            is_code_coverage_dead_code_cgu: false,
+        }
     }
 
     pub fn name(&self) -> Symbol {
@@ -304,6 +313,15 @@ impl<'tcx> CodegenUnit<'tcx> {
         &mut self.items
     }
 
+    pub fn is_code_coverage_dead_code_cgu(&self) -> bool {
+        self.is_code_coverage_dead_code_cgu
+    }
+
+    /// Marks this CGU as the one used to contain code coverage information for dead code.
+    pub fn make_code_coverage_dead_code_cgu(&mut self) {
+        self.is_code_coverage_dead_code_cgu = true;
+    }
+
     pub fn mangle_name(human_readable_name: &str) -> String {
         // We generate a 80 bit hash from the name. This should be enough to
         // avoid collisions and is still reasonably short for filenames.
@@ -404,9 +422,11 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for CodegenUnit<'tcx> {
             // The size estimate is not relevant to the hash
             size_estimate: _,
             primary: _,
+            is_code_coverage_dead_code_cgu,
         } = *self;
 
         name.hash_stable(hcx, hasher);
+        is_code_coverage_dead_code_cgu.hash_stable(hcx, hasher);
 
         let mut items: Vec<(Fingerprint, _)> = items
             .iter()
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 6dd1ee893a4..3772f1c9fea 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -386,16 +386,6 @@ rustc_queries! {
         storage(ArenaCacheSelector<'tcx>)
     }
 
-    /// Returns the name of the file that contains the function body, if instrumented for coverage.
-    query covered_file_name(key: DefId) -> Option<Symbol> {
-        desc {
-            |tcx| "retrieving the covered file name, if instrumented, for `{}`",
-            tcx.def_path_str(key)
-        }
-        storage(ArenaCacheSelector<'tcx>)
-        cache_on_disk_if { key.is_local() }
-    }
-
     /// Returns the `CodeRegions` for a function that has instrumented coverage, in case the
     /// function was optimized out before codegen, and before being added to the Coverage Map.
     query covered_code_regions(key: DefId) -> Vec<&'tcx mir::coverage::CodeRegion> {
diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
index 1721fb5cde0..46de6d939a1 100644
--- a/compiler/rustc_mir_transform/src/coverage/query.rs
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -9,7 +9,6 @@ use rustc_span::def_id::DefId;
 /// A `query` provider for retrieving coverage information injected into MIR.
 pub(crate) fn provide(providers: &mut Providers) {
     providers.coverageinfo = |tcx, def_id| coverageinfo(tcx, def_id);
-    providers.covered_file_name = |tcx, def_id| covered_file_name(tcx, def_id);
     providers.covered_code_regions = |tcx, def_id| covered_code_regions(tcx, def_id);
 }
 
@@ -137,25 +136,6 @@ fn coverageinfo<'tcx>(tcx: TyCtxt<'tcx>, instance_def: ty::InstanceDef<'tcx>) ->
     coverage_visitor.info
 }
 
-fn covered_file_name(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
-    if tcx.is_mir_available(def_id) {
-        let body = mir_body(tcx, def_id);
-        for bb_data in body.basic_blocks().iter() {
-            for statement in bb_data.statements.iter() {
-                if let StatementKind::Coverage(box ref coverage) = statement.kind {
-                    if let Some(code_region) = coverage.code_region.as_ref() {
-                        if is_inlined(body, statement) {
-                            continue;
-                        }
-                        return Some(code_region.file_name);
-                    }
-                }
-            }
-        }
-    }
-    return None;
-}
-
 fn covered_code_regions<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Vec<&'tcx CodeRegion> {
     let body = mir_body(tcx, def_id);
     body.basic_blocks()
diff --git a/compiler/rustc_monomorphize/src/partitioning/mod.rs b/compiler/rustc_monomorphize/src/partitioning/mod.rs
index dc22ffc6747..67597a0d7b4 100644
--- a/compiler/rustc_monomorphize/src/partitioning/mod.rs
+++ b/compiler/rustc_monomorphize/src/partitioning/mod.rs
@@ -201,6 +201,40 @@ pub fn partition<'tcx>(
         partitioner.internalize_symbols(cx, &mut post_inlining);
     }
 
+    let instrument_dead_code =
+        tcx.sess.instrument_coverage() && !tcx.sess.instrument_coverage_except_unused_functions();
+
+    if instrument_dead_code {
+        assert!(
+            post_inlining.codegen_units.len() > 0,
+            "There must be at least one CGU that code coverage data can be generated in."
+        );
+
+        // Find the smallest CGU that has exported symbols and put the dead
+        // function stubs in that CGU. We look for exported symbols to increase
+        // the likelihood the linker won't throw away the dead functions.
+        // FIXME(#92165): In order to truly resolve this, we need to make sure
+        // the object file (CGU) containing the dead function stubs is included
+        // in the final binary. This will probably require forcing these
+        // function symbols to be included via `-u` or `/include` linker args.
+        let mut cgus: Vec<_> = post_inlining.codegen_units.iter_mut().collect();
+        cgus.sort_by_key(|cgu| cgu.size_estimate());
+
+        let dead_code_cgu = if let Some(cgu) = cgus
+            .into_iter()
+            .rev()
+            .filter(|cgu| cgu.items().iter().any(|(_, (linkage, _))| *linkage == Linkage::External))
+            .next()
+        {
+            cgu
+        } else {
+            // If there are no CGUs that have externally linked items,
+            // then we just pick the first CGU as a fallback.
+            &mut post_inlining.codegen_units[0]
+        };
+        dead_code_cgu.make_code_coverage_dead_code_cgu();
+    }
+
     // Finally, sort by codegen unit name, so that we get deterministic results.
     let PostInliningPartitioning {
         codegen_units: mut result,
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
index 12ca3faeb37..d662f61e2cf 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
@@ -4,7 +4,9 @@ use crate::infer::canonical::{
 use crate::infer::{InferCtxt, InferOk};
 use crate::traits::query::Fallible;
 use crate::traits::ObligationCause;
-use rustc_infer::infer::canonical::Canonical;
+use rustc_infer::infer::canonical::{Canonical, Certainty};
+use rustc_infer::traits::query::NoSolution;
+use rustc_infer::traits::PredicateObligations;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::{ParamEnvAnd, TyCtxt};
 use std::fmt;
@@ -17,7 +19,6 @@ pub mod implied_outlives_bounds;
 pub mod normalize;
 pub mod outlives;
 pub mod prove_predicate;
-use self::prove_predicate::ProvePredicate;
 pub mod subtype;
 
 pub use rustc_middle::traits::query::type_op::*;
@@ -80,9 +81,14 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Copy + TypeFoldable<'tcx> + 'tcx {
         query_key: ParamEnvAnd<'tcx, Self>,
         infcx: &InferCtxt<'_, 'tcx>,
         output_query_region_constraints: &mut QueryRegionConstraints<'tcx>,
-    ) -> Fallible<(Self::QueryResponse, Option<Canonical<'tcx, ParamEnvAnd<'tcx, Self>>>)> {
+    ) -> Fallible<(
+        Self::QueryResponse,
+        Option<Canonical<'tcx, ParamEnvAnd<'tcx, Self>>>,
+        PredicateObligations<'tcx>,
+        Certainty,
+    )> {
         if let Some(result) = QueryTypeOp::try_fast_path(infcx.tcx, &query_key) {
-            return Ok((result, None));
+            return Ok((result, None, vec![], Certainty::Proven));
         }
 
         // FIXME(#33684) -- We need to use
@@ -104,20 +110,7 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Copy + TypeFoldable<'tcx> + 'tcx {
                 output_query_region_constraints,
             )?;
 
-        // Typically, instantiating NLL query results does not
-        // create obligations. However, in some cases there
-        // are unresolved type variables, and unify them *can*
-        // create obligations. In that case, we have to go
-        // fulfill them. We do this via a (recursive) query.
-        for obligation in obligations {
-            let ((), _) = ProvePredicate::fully_perform_into(
-                obligation.param_env.and(ProvePredicate::new(obligation.predicate)),
-                infcx,
-                output_query_region_constraints,
-            )?;
-        }
-
-        Ok((value, Some(canonical_self)))
+        Ok((value, Some(canonical_self), obligations, canonical_result.value.certainty))
     }
 }
 
@@ -129,9 +122,39 @@ where
 
     fn fully_perform(self, infcx: &InferCtxt<'_, 'tcx>) -> Fallible<TypeOpOutput<'tcx, Self>> {
         let mut region_constraints = QueryRegionConstraints::default();
-        let (output, canonicalized_query) =
+        let (output, canonicalized_query, mut obligations, _) =
             Q::fully_perform_into(self, infcx, &mut region_constraints)?;
 
+        // Typically, instantiating NLL query results does not
+        // create obligations. However, in some cases there
+        // are unresolved type variables, and unify them *can*
+        // create obligations. In that case, we have to go
+        // fulfill them. We do this via a (recursive) query.
+        while !obligations.is_empty() {
+            trace!("{:#?}", obligations);
+            let mut progress = false;
+            for obligation in std::mem::take(&mut obligations) {
+                let obligation = infcx.resolve_vars_if_possible(obligation);
+                match ProvePredicate::fully_perform_into(
+                    obligation.param_env.and(ProvePredicate::new(obligation.predicate)),
+                    infcx,
+                    &mut region_constraints,
+                ) {
+                    Ok(((), _, new, certainty)) => {
+                        obligations.extend(new);
+                        progress = true;
+                        if let Certainty::Ambiguous = certainty {
+                            obligations.push(obligation);
+                        }
+                    }
+                    Err(_) => obligations.push(obligation),
+                }
+            }
+            if !progress {
+                return Err(NoSolution);
+            }
+        }
+
         // Promote the final query-region-constraints into a
         // (optional) ref-counted vector:
         let region_constraints =
diff --git a/library/std/src/error.rs b/library/std/src/error.rs
index 526a1b92b19..643108b88bf 100644
--- a/library/std/src/error.rs
+++ b/library/std/src/error.rs
@@ -25,7 +25,7 @@ use crate::backtrace::Backtrace;
 use crate::borrow::Cow;
 use crate::cell;
 use crate::char;
-use crate::fmt::{self, Debug, Display};
+use crate::fmt::{self, Debug, Display, Write};
 use crate::mem::transmute;
 use crate::num;
 use crate::str;
@@ -63,7 +63,7 @@ pub trait Error: Debug + Display {
     ///
     /// #[derive(Debug)]
     /// struct SuperError {
-    ///     side: SuperErrorSideKick,
+    ///     source: SuperErrorSideKick,
     /// }
     ///
     /// impl fmt::Display for SuperError {
@@ -74,7 +74,7 @@ pub trait Error: Debug + Display {
     ///
     /// impl Error for SuperError {
     ///     fn source(&self) -> Option<&(dyn Error + 'static)> {
-    ///         Some(&self.side)
+    ///         Some(&self.source)
     ///     }
     /// }
     ///
@@ -90,7 +90,7 @@ pub trait Error: Debug + Display {
     /// impl Error for SuperErrorSideKick {}
     ///
     /// fn get_super_error() -> Result<(), SuperError> {
-    ///     Err(SuperError { side: SuperErrorSideKick })
+    ///     Err(SuperError { source: SuperErrorSideKick })
     /// }
     ///
     /// fn main() {
@@ -810,3 +810,642 @@ impl dyn Error + Send + Sync {
         })
     }
 }
+
+/// An error reporter that print's an error and its sources.
+///
+/// Report also exposes configuration options for formatting the error chain, either entirely on a
+/// single line, or in multi-line format with each cause in the error chain on a new line.
+///
+/// `Report` only requires that the wrapped error implements `Error`. It doesn't require that the
+/// wrapped error be `Send`, `Sync`, or `'static`.
+///
+/// # Examples
+///
+/// ```rust
+/// #![feature(error_reporter)]
+/// use std::error::{Error, Report};
+/// use std::fmt;
+///
+/// #[derive(Debug)]
+/// struct SuperError {
+///     source: SuperErrorSideKick,
+/// }
+///
+/// impl fmt::Display for SuperError {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         write!(f, "SuperError is here!")
+///     }
+/// }
+///
+/// impl Error for SuperError {
+///     fn source(&self) -> Option<&(dyn Error + 'static)> {
+///         Some(&self.source)
+///     }
+/// }
+///
+/// #[derive(Debug)]
+/// struct SuperErrorSideKick;
+///
+/// impl fmt::Display for SuperErrorSideKick {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         write!(f, "SuperErrorSideKick is here!")
+///     }
+/// }
+///
+/// impl Error for SuperErrorSideKick {}
+///
+/// fn get_super_error() -> Result<(), SuperError> {
+///     Err(SuperError { source: SuperErrorSideKick })
+/// }
+///
+/// fn main() {
+///     match get_super_error() {
+///         Err(e) => println!("Error: {}", Report::new(e)),
+///         _ => println!("No error"),
+///     }
+/// }
+/// ```
+///
+/// This example produces the following output:
+///
+/// ```console
+/// Error: SuperError is here!: SuperErrorSideKick is here!
+/// ```
+///
+/// ## Output consistency
+///
+/// Report prints the same output via `Display` and `Debug`, so it works well with
+/// [`Result::unwrap`]/[`Result::expect`] which print their `Err` variant via `Debug`:
+///
+/// ```should_panic
+/// #![feature(error_reporter)]
+/// use std::error::Report;
+/// # use std::error::Error;
+/// # use std::fmt;
+/// # #[derive(Debug)]
+/// # struct SuperError {
+/// #     source: SuperErrorSideKick,
+/// # }
+/// # impl fmt::Display for SuperError {
+/// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+/// #         write!(f, "SuperError is here!")
+/// #     }
+/// # }
+/// # impl Error for SuperError {
+/// #     fn source(&self) -> Option<&(dyn Error + 'static)> {
+/// #         Some(&self.source)
+/// #     }
+/// # }
+/// # #[derive(Debug)]
+/// # struct SuperErrorSideKick;
+/// # impl fmt::Display for SuperErrorSideKick {
+/// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+/// #         write!(f, "SuperErrorSideKick is here!")
+/// #     }
+/// # }
+/// # impl Error for SuperErrorSideKick {}
+/// # fn get_super_error() -> Result<(), SuperError> {
+/// #     Err(SuperError { source: SuperErrorSideKick })
+/// # }
+///
+/// get_super_error().map_err(Report::new).unwrap();
+/// ```
+///
+/// This example produces the following output:
+///
+/// ```console
+/// thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: SuperError is here!: SuperErrorSideKick is here!', src/error.rs:34:40
+/// note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+/// ```
+///
+/// ## Return from `main`
+///
+/// `Report` also implements `From` for all types that implement [`Error`], this when combined with
+/// the `Debug` output means `Report` is an ideal starting place for formatting errors returned
+/// from `main`.
+///
+/// ```should_panic
+/// #![feature(error_reporter)]
+/// use std::error::Report;
+/// # use std::error::Error;
+/// # use std::fmt;
+/// # #[derive(Debug)]
+/// # struct SuperError {
+/// #     source: SuperErrorSideKick,
+/// # }
+/// # impl fmt::Display for SuperError {
+/// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+/// #         write!(f, "SuperError is here!")
+/// #     }
+/// # }
+/// # impl Error for SuperError {
+/// #     fn source(&self) -> Option<&(dyn Error + 'static)> {
+/// #         Some(&self.source)
+/// #     }
+/// # }
+/// # #[derive(Debug)]
+/// # struct SuperErrorSideKick;
+/// # impl fmt::Display for SuperErrorSideKick {
+/// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+/// #         write!(f, "SuperErrorSideKick is here!")
+/// #     }
+/// # }
+/// # impl Error for SuperErrorSideKick {}
+/// # fn get_super_error() -> Result<(), SuperError> {
+/// #     Err(SuperError { source: SuperErrorSideKick })
+/// # }
+///
+/// fn main() -> Result<(), Report> {
+///     get_super_error()?;
+///     Ok(())
+/// }
+/// ```
+///
+/// This example produces the following output:
+///
+/// ```console
+/// Error: SuperError is here!: SuperErrorSideKick is here!
+/// ```
+///
+/// **Note**: `Report`s constructed via `?` and `From` will be configured to use the single line
+/// output format, if you want to make sure your `Report`s are pretty printed and include backtrace
+/// you will need to manually convert and enable those flags.
+///
+/// ```should_panic
+/// #![feature(error_reporter)]
+/// use std::error::Report;
+/// # use std::error::Error;
+/// # use std::fmt;
+/// # #[derive(Debug)]
+/// # struct SuperError {
+/// #     source: SuperErrorSideKick,
+/// # }
+/// # impl fmt::Display for SuperError {
+/// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+/// #         write!(f, "SuperError is here!")
+/// #     }
+/// # }
+/// # impl Error for SuperError {
+/// #     fn source(&self) -> Option<&(dyn Error + 'static)> {
+/// #         Some(&self.source)
+/// #     }
+/// # }
+/// # #[derive(Debug)]
+/// # struct SuperErrorSideKick;
+/// # impl fmt::Display for SuperErrorSideKick {
+/// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+/// #         write!(f, "SuperErrorSideKick is here!")
+/// #     }
+/// # }
+/// # impl Error for SuperErrorSideKick {}
+/// # fn get_super_error() -> Result<(), SuperError> {
+/// #     Err(SuperError { source: SuperErrorSideKick })
+/// # }
+///
+/// fn main() -> Result<(), Report> {
+///     get_super_error()
+///         .map_err(Report::from)
+///         .map_err(|r| r.pretty(true).show_backtrace(true))?;
+///     Ok(())
+/// }
+/// ```
+///
+/// This example produces the following output:
+///
+/// ```console
+/// Error: SuperError is here!
+///
+/// Caused by:
+///       SuperErrorSideKick is here!
+/// ```
+#[unstable(feature = "error_reporter", issue = "90172")]
+pub struct Report<E = Box<dyn Error>> {
+    /// The error being reported.
+    error: E,
+    /// Whether a backtrace should be included as part of the report.
+    show_backtrace: bool,
+    /// Whether the report should be pretty-printed.
+    pretty: bool,
+}
+
+impl<E> Report<E>
+where
+    Report<E>: From<E>,
+{
+    /// Create a new `Report` from an input error.
+    #[unstable(feature = "error_reporter", issue = "90172")]
+    pub fn new(error: E) -> Report<E> {
+        Self::from(error)
+    }
+}
+
+impl<E> Report<E> {
+    /// Enable pretty-printing the report across multiple lines.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// #![feature(error_reporter)]
+    /// use std::error::Report;
+    /// # use std::error::Error;
+    /// # use std::fmt;
+    /// # #[derive(Debug)]
+    /// # struct SuperError {
+    /// #     source: SuperErrorSideKick,
+    /// # }
+    /// # impl fmt::Display for SuperError {
+    /// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    /// #         write!(f, "SuperError is here!")
+    /// #     }
+    /// # }
+    /// # impl Error for SuperError {
+    /// #     fn source(&self) -> Option<&(dyn Error + 'static)> {
+    /// #         Some(&self.source)
+    /// #     }
+    /// # }
+    /// # #[derive(Debug)]
+    /// # struct SuperErrorSideKick;
+    /// # impl fmt::Display for SuperErrorSideKick {
+    /// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    /// #         write!(f, "SuperErrorSideKick is here!")
+    /// #     }
+    /// # }
+    /// # impl Error for SuperErrorSideKick {}
+    ///
+    /// let error = SuperError { source: SuperErrorSideKick };
+    /// let report = Report::new(error).pretty(true);
+    /// eprintln!("Error: {:?}", report);
+    /// ```
+    ///
+    /// This example produces the following output:
+    ///
+    /// ```console
+    /// Error: SuperError is here!
+    ///
+    /// Caused by:
+    ///       SuperErrorSideKick is here!
+    /// ```
+    ///
+    /// When there are multiple source errors the causes will be numbered in order of iteration
+    /// starting from the outermost error.
+    ///
+    /// ```rust
+    /// #![feature(error_reporter)]
+    /// use std::error::Report;
+    /// # use std::error::Error;
+    /// # use std::fmt;
+    /// # #[derive(Debug)]
+    /// # struct SuperError {
+    /// #     source: SuperErrorSideKick,
+    /// # }
+    /// # impl fmt::Display for SuperError {
+    /// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    /// #         write!(f, "SuperError is here!")
+    /// #     }
+    /// # }
+    /// # impl Error for SuperError {
+    /// #     fn source(&self) -> Option<&(dyn Error + 'static)> {
+    /// #         Some(&self.source)
+    /// #     }
+    /// # }
+    /// # #[derive(Debug)]
+    /// # struct SuperErrorSideKick {
+    /// #     source: SuperErrorSideKickSideKick,
+    /// # }
+    /// # impl fmt::Display for SuperErrorSideKick {
+    /// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    /// #         write!(f, "SuperErrorSideKick is here!")
+    /// #     }
+    /// # }
+    /// # impl Error for SuperErrorSideKick {
+    /// #     fn source(&self) -> Option<&(dyn Error + 'static)> {
+    /// #         Some(&self.source)
+    /// #     }
+    /// # }
+    /// # #[derive(Debug)]
+    /// # struct SuperErrorSideKickSideKick;
+    /// # impl fmt::Display for SuperErrorSideKickSideKick {
+    /// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    /// #         write!(f, "SuperErrorSideKickSideKick is here!")
+    /// #     }
+    /// # }
+    /// # impl Error for SuperErrorSideKickSideKick { }
+    ///
+    /// let source = SuperErrorSideKickSideKick;
+    /// let source = SuperErrorSideKick { source };
+    /// let error = SuperError { source };
+    /// let report = Report::new(error).pretty(true);
+    /// eprintln!("Error: {:?}", report);
+    /// ```
+    ///
+    /// This example produces the following output:
+    ///
+    /// ```console
+    /// Error: SuperError is here!
+    ///
+    /// Caused by:
+    ///    0: SuperErrorSideKick is here!
+    ///    1: SuperErrorSideKickSideKick is here!
+    /// ```
+    #[unstable(feature = "error_reporter", issue = "90172")]
+    pub fn pretty(mut self, pretty: bool) -> Self {
+        self.pretty = pretty;
+        self
+    }
+
+    /// Display backtrace if available when using pretty output format.
+    ///
+    /// # Examples
+    ///
+    /// **Note**: Report will search for the first `Backtrace` it can find starting from the
+    /// outermost error. In this example it will display the backtrace from the second error in the
+    /// chain, `SuperErrorSideKick`.
+    ///
+    /// ```rust
+    /// #![feature(error_reporter)]
+    /// #![feature(backtrace)]
+    /// # use std::error::Error;
+    /// # use std::fmt;
+    /// use std::error::Report;
+    /// use std::backtrace::Backtrace;
+    ///
+    /// # #[derive(Debug)]
+    /// # struct SuperError {
+    /// #     source: SuperErrorSideKick,
+    /// # }
+    /// # impl fmt::Display for SuperError {
+    /// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    /// #         write!(f, "SuperError is here!")
+    /// #     }
+    /// # }
+    /// # impl Error for SuperError {
+    /// #     fn source(&self) -> Option<&(dyn Error + 'static)> {
+    /// #         Some(&self.source)
+    /// #     }
+    /// # }
+    /// #[derive(Debug)]
+    /// struct SuperErrorSideKick {
+    ///     backtrace: Backtrace,
+    /// }
+    ///
+    /// impl SuperErrorSideKick {
+    ///     fn new() -> SuperErrorSideKick {
+    ///         SuperErrorSideKick { backtrace: Backtrace::force_capture() }
+    ///     }
+    /// }
+    ///
+    /// impl Error for SuperErrorSideKick {
+    ///     fn backtrace(&self) -> Option<&Backtrace> {
+    ///         Some(&self.backtrace)
+    ///     }
+    /// }
+    ///
+    /// // The rest of the example is unchanged ...
+    /// # impl fmt::Display for SuperErrorSideKick {
+    /// #     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    /// #         write!(f, "SuperErrorSideKick is here!")
+    /// #     }
+    /// # }
+    ///
+    /// let source = SuperErrorSideKick::new();
+    /// let error = SuperError { source };
+    /// let report = Report::new(error).pretty(true).show_backtrace(true);
+    /// eprintln!("Error: {:?}", report);
+    /// ```
+    ///
+    /// This example produces something similar to the following output:
+    ///
+    /// ```console
+    /// Error: SuperError is here!
+    ///
+    /// Caused by:
+    ///       SuperErrorSideKick is here!
+    ///
+    /// Stack backtrace:
+    ///    0: rust_out::main::_doctest_main_src_error_rs_1158_0::SuperErrorSideKick::new
+    ///    1: rust_out::main::_doctest_main_src_error_rs_1158_0
+    ///    2: rust_out::main
+    ///    3: core::ops::function::FnOnce::call_once
+    ///    4: std::sys_common::backtrace::__rust_begin_short_backtrace
+    ///    5: std::rt::lang_start::{{closure}}
+    ///    6: std::panicking::try
+    ///    7: std::rt::lang_start_internal
+    ///    8: std::rt::lang_start
+    ///    9: main
+    ///   10: __libc_start_main
+    ///   11: _start
+    /// ```
+    #[unstable(feature = "error_reporter", issue = "90172")]
+    pub fn show_backtrace(mut self, show_backtrace: bool) -> Self {
+        self.show_backtrace = show_backtrace;
+        self
+    }
+}
+
+impl<E> Report<E>
+where
+    E: Error,
+{
+    fn backtrace(&self) -> Option<&Backtrace> {
+        // have to grab the backtrace on the first error directly since that error may not be
+        // 'static
+        let backtrace = self.error.backtrace();
+        let backtrace = backtrace.or_else(|| {
+            self.error
+                .source()
+                .map(|source| source.chain().find_map(|source| source.backtrace()))
+                .flatten()
+        });
+        backtrace
+    }
+
+    /// Format the report as a single line.
+    #[unstable(feature = "error_reporter", issue = "90172")]
+    fn fmt_singleline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.error)?;
+
+        let sources = self.error.source().into_iter().flat_map(<dyn Error>::chain);
+
+        for cause in sources {
+            write!(f, ": {}", cause)?;
+        }
+
+        Ok(())
+    }
+
+    /// Format the report as multiple lines, with each error cause on its own line.
+    #[unstable(feature = "error_reporter", issue = "90172")]
+    fn fmt_multiline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let error = &self.error;
+
+        write!(f, "{}", error)?;
+
+        if let Some(cause) = error.source() {
+            write!(f, "\n\nCaused by:")?;
+
+            let multiple = cause.source().is_some();
+
+            for (ind, error) in cause.chain().enumerate() {
+                writeln!(f)?;
+                let mut indented = Indented { inner: f };
+                if multiple {
+                    write!(indented, "{: >4}: {}", ind, error)?;
+                } else {
+                    write!(indented, "      {}", error)?;
+                }
+            }
+        }
+
+        if self.show_backtrace {
+            let backtrace = self.backtrace();
+
+            if let Some(backtrace) = backtrace {
+                let backtrace = backtrace.to_string();
+
+                f.write_str("\n\nStack backtrace:\n")?;
+                f.write_str(backtrace.trim_end())?;
+            }
+        }
+
+        Ok(())
+    }
+}
+
+impl Report<Box<dyn Error>> {
+    fn backtrace(&self) -> Option<&Backtrace> {
+        // have to grab the backtrace on the first error directly since that error may not be
+        // 'static
+        let backtrace = self.error.backtrace();
+        let backtrace = backtrace.or_else(|| {
+            self.error
+                .source()
+                .map(|source| source.chain().find_map(|source| source.backtrace()))
+                .flatten()
+        });
+        backtrace
+    }
+
+    /// Format the report as a single line.
+    #[unstable(feature = "error_reporter", issue = "90172")]
+    fn fmt_singleline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.error)?;
+
+        let sources = self.error.source().into_iter().flat_map(<dyn Error>::chain);
+
+        for cause in sources {
+            write!(f, ": {}", cause)?;
+        }
+
+        Ok(())
+    }
+
+    /// Format the report as multiple lines, with each error cause on its own line.
+    #[unstable(feature = "error_reporter", issue = "90172")]
+    fn fmt_multiline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let error = &self.error;
+
+        write!(f, "{}", error)?;
+
+        if let Some(cause) = error.source() {
+            write!(f, "\n\nCaused by:")?;
+
+            let multiple = cause.source().is_some();
+
+            for (ind, error) in cause.chain().enumerate() {
+                writeln!(f)?;
+                let mut indented = Indented { inner: f };
+                if multiple {
+                    write!(indented, "{: >4}: {}", ind, error)?;
+                } else {
+                    write!(indented, "      {}", error)?;
+                }
+            }
+        }
+
+        if self.show_backtrace {
+            let backtrace = self.backtrace();
+
+            if let Some(backtrace) = backtrace {
+                let backtrace = backtrace.to_string();
+
+                f.write_str("\n\nStack backtrace:\n")?;
+                f.write_str(backtrace.trim_end())?;
+            }
+        }
+
+        Ok(())
+    }
+}
+
+#[unstable(feature = "error_reporter", issue = "90172")]
+impl<E> From<E> for Report<E>
+where
+    E: Error,
+{
+    fn from(error: E) -> Self {
+        Report { error, show_backtrace: false, pretty: false }
+    }
+}
+
+#[unstable(feature = "error_reporter", issue = "90172")]
+impl<'a, E> From<E> for Report<Box<dyn Error + 'a>>
+where
+    E: Error + 'a,
+{
+    fn from(error: E) -> Self {
+        let error = box error;
+        Report { error, show_backtrace: false, pretty: false }
+    }
+}
+
+#[unstable(feature = "error_reporter", issue = "90172")]
+impl<E> fmt::Display for Report<E>
+where
+    E: Error,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.pretty { self.fmt_multiline(f) } else { self.fmt_singleline(f) }
+    }
+}
+
+#[unstable(feature = "error_reporter", issue = "90172")]
+impl fmt::Display for Report<Box<dyn Error>> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.pretty { self.fmt_multiline(f) } else { self.fmt_singleline(f) }
+    }
+}
+
+// This type intentionally outputs the same format for `Display` and `Debug`for
+// situations where you unwrap a `Report` or return it from main.
+#[unstable(feature = "error_reporter", issue = "90172")]
+impl<E> fmt::Debug for Report<E>
+where
+    Report<E>: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+/// Wrapper type for indenting the inner source.
+struct Indented<'a, D> {
+    inner: &'a mut D,
+}
+
+impl<T> Write for Indented<'_, T>
+where
+    T: Write,
+{
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        for (i, line) in s.split('\n').enumerate() {
+            if i > 0 {
+                self.inner.write_char('\n')?;
+                self.inner.write_str("      ")?;
+            }
+
+            self.inner.write_str(line)?;
+        }
+
+        Ok(())
+    }
+}
diff --git a/library/std/src/error/tests.rs b/library/std/src/error/tests.rs
index 66d6924f34d..eae5f43ff3c 100644
--- a/library/std/src/error/tests.rs
+++ b/library/std/src/error/tests.rs
@@ -35,3 +35,408 @@ fn downcasting() {
         Err(e) => assert_eq!(*e.downcast::<A>().unwrap(), A),
     }
 }
+
+use crate::backtrace::Backtrace;
+use crate::error::Report;
+
+#[derive(Debug)]
+struct SuperError {
+    source: SuperErrorSideKick,
+}
+
+impl fmt::Display for SuperError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "SuperError is here!")
+    }
+}
+
+impl Error for SuperError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        Some(&self.source)
+    }
+}
+
+#[derive(Debug)]
+struct SuperErrorSideKick;
+
+impl fmt::Display for SuperErrorSideKick {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "SuperErrorSideKick is here!")
+    }
+}
+
+impl Error for SuperErrorSideKick {}
+
+#[test]
+fn single_line_formatting() {
+    let error = SuperError { source: SuperErrorSideKick };
+    let report = Report::new(&error);
+    let actual = report.to_string();
+    let expected = String::from("SuperError is here!: SuperErrorSideKick is here!");
+
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn multi_line_formatting() {
+    let error = SuperError { source: SuperErrorSideKick };
+    let report = Report::new(&error).pretty(true);
+    let actual = report.to_string();
+    let expected = String::from(
+        "\
+SuperError is here!
+
+Caused by:
+      SuperErrorSideKick is here!",
+    );
+
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn error_with_no_sources_formats_single_line_correctly() {
+    let report = Report::new(SuperErrorSideKick);
+    let actual = report.to_string();
+    let expected = String::from("SuperErrorSideKick is here!");
+
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn error_with_no_sources_formats_multi_line_correctly() {
+    let report = Report::new(SuperErrorSideKick).pretty(true);
+    let actual = report.to_string();
+    let expected = String::from("SuperErrorSideKick is here!");
+
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn error_with_backtrace_outputs_correctly_with_one_source() {
+    let trace = Backtrace::force_capture();
+    let expected = format!(
+        "\
+The source of the error
+
+Caused by:
+      Error with backtrace
+
+Stack backtrace:
+{}",
+        trace
+    );
+    let error = GenericError::new("Error with backtrace");
+    let mut error = GenericError::new_with_source("The source of the error", error);
+    error.backtrace = Some(trace);
+    let report = Report::new(error).pretty(true).show_backtrace(true);
+
+    println!("Error: {}", report);
+    assert_eq!(expected.trim_end(), report.to_string());
+}
+
+#[test]
+fn error_with_backtrace_outputs_correctly_with_two_sources() {
+    let trace = Backtrace::force_capture();
+    let expected = format!(
+        "\
+Error with two sources
+
+Caused by:
+   0: The source of the error
+   1: Error with backtrace
+
+Stack backtrace:
+{}",
+        trace
+    );
+    let mut error = GenericError::new("Error with backtrace");
+    error.backtrace = Some(trace);
+    let error = GenericError::new_with_source("The source of the error", error);
+    let error = GenericError::new_with_source("Error with two sources", error);
+    let report = Report::new(error).pretty(true).show_backtrace(true);
+
+    println!("Error: {}", report);
+    assert_eq!(expected.trim_end(), report.to_string());
+}
+
+#[derive(Debug)]
+struct GenericError<D> {
+    message: D,
+    backtrace: Option<Backtrace>,
+    source: Option<Box<dyn Error + 'static>>,
+}
+
+impl<D> GenericError<D> {
+    fn new(message: D) -> GenericError<D> {
+        Self { message, backtrace: None, source: None }
+    }
+
+    fn new_with_source<E>(message: D, source: E) -> GenericError<D>
+    where
+        E: Error + 'static,
+    {
+        let source: Box<dyn Error + 'static> = Box::new(source);
+        let source = Some(source);
+        GenericError { message, backtrace: None, source }
+    }
+}
+
+impl<D> fmt::Display for GenericError<D>
+where
+    D: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.message, f)
+    }
+}
+
+impl<D> Error for GenericError<D>
+where
+    D: fmt::Debug + fmt::Display,
+{
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        self.source.as_deref()
+    }
+
+    fn backtrace(&self) -> Option<&Backtrace> {
+        self.backtrace.as_ref()
+    }
+}
+
+#[test]
+fn error_formats_single_line_with_rude_display_impl() {
+    #[derive(Debug)]
+    struct MyMessage;
+
+    impl fmt::Display for MyMessage {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.write_str("line 1\nline 2")?;
+            f.write_str("\nline 3\nline 4\n")?;
+            f.write_str("line 5\nline 6")?;
+            Ok(())
+        }
+    }
+
+    let error = GenericError::new(MyMessage);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let report = Report::new(error);
+    let expected = "\
+line 1
+line 2
+line 3
+line 4
+line 5
+line 6: line 1
+line 2
+line 3
+line 4
+line 5
+line 6: line 1
+line 2
+line 3
+line 4
+line 5
+line 6: line 1
+line 2
+line 3
+line 4
+line 5
+line 6";
+
+    let actual = report.to_string();
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn error_formats_multi_line_with_rude_display_impl() {
+    #[derive(Debug)]
+    struct MyMessage;
+
+    impl fmt::Display for MyMessage {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.write_str("line 1\nline 2")?;
+            f.write_str("\nline 3\nline 4\n")?;
+            f.write_str("line 5\nline 6")?;
+            Ok(())
+        }
+    }
+
+    let error = GenericError::new(MyMessage);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let report = Report::new(error).pretty(true);
+    let expected = "line 1
+line 2
+line 3
+line 4
+line 5
+line 6
+
+Caused by:
+   0: line 1
+      line 2
+      line 3
+      line 4
+      line 5
+      line 6
+   1: line 1
+      line 2
+      line 3
+      line 4
+      line 5
+      line 6
+   2: line 1
+      line 2
+      line 3
+      line 4
+      line 5
+      line 6";
+
+    let actual = report.to_string();
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn errors_that_start_with_newline_formats_correctly() {
+    #[derive(Debug)]
+    struct MyMessage;
+
+    impl fmt::Display for MyMessage {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.write_str("\nThe message\n")
+        }
+    }
+
+    let error = GenericError::new(MyMessage);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let report = Report::new(error).pretty(true);
+    let expected = "
+The message
+
+
+Caused by:
+   0: \
+\n      The message
+      \
+\n   1: \
+\n      The message
+      ";
+
+    let actual = report.to_string();
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn errors_with_multiple_writes_on_same_line_dont_insert_erroneous_newlines() {
+    #[derive(Debug)]
+    struct MyMessage;
+
+    impl fmt::Display for MyMessage {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.write_str("The message")?;
+            f.write_str(" goes on")?;
+            f.write_str(" and on.")
+        }
+    }
+
+    let error = GenericError::new(MyMessage);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let report = Report::new(error).pretty(true);
+    let expected = "\
+The message goes on and on.
+
+Caused by:
+   0: The message goes on and on.
+   1: The message goes on and on.";
+
+    let actual = report.to_string();
+    println!("{}", actual);
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn errors_with_string_interpolation_formats_correctly() {
+    #[derive(Debug)]
+    struct MyMessage(usize);
+
+    impl fmt::Display for MyMessage {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(f, "Got an error code: ({}). ", self.0)?;
+            write!(f, "What would you like to do in response?")
+        }
+    }
+
+    let error = GenericError::new(MyMessage(10));
+    let error = GenericError::new_with_source(MyMessage(20), error);
+    let report = Report::new(error).pretty(true);
+    let expected = "\
+Got an error code: (20). What would you like to do in response?
+
+Caused by:
+      Got an error code: (10). What would you like to do in response?";
+    let actual = report.to_string();
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn empty_lines_mid_message() {
+    #[derive(Debug)]
+    struct MyMessage;
+
+    impl fmt::Display for MyMessage {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.write_str("line 1\n\nline 2")
+        }
+    }
+
+    let error = GenericError::new(MyMessage);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let report = Report::new(error).pretty(true);
+    let expected = "\
+line 1
+
+line 2
+
+Caused by:
+   0: line 1
+      \
+\n      line 2
+   1: line 1
+      \
+\n      line 2";
+
+    let actual = report.to_string();
+    assert_eq!(expected, actual);
+}
+
+#[test]
+fn only_one_source() {
+    #[derive(Debug)]
+    struct MyMessage;
+
+    impl fmt::Display for MyMessage {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.write_str("line 1\nline 2")
+        }
+    }
+
+    let error = GenericError::new(MyMessage);
+    let error = GenericError::new_with_source(MyMessage, error);
+    let report = Report::new(error).pretty(true);
+    let expected = "\
+line 1
+line 2
+
+Caused by:
+      line 1
+      line 2";
+
+    let actual = report.to_string();
+    assert_eq!(expected, actual);
+}
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index f0e9b716081..b14430d10e9 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -17,6 +17,8 @@ use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::mir::interpret::ConstValue;
 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
 use rustc_middle::ty::{self, DefIdTree, TyCtxt};
+use rustc_session::parse::ParseSess;
+use rustc_span::source_map::FilePathMapping;
 use rustc_span::symbol::{kw, sym, Symbol};
 use std::fmt::Write as _;
 use std::mem;
@@ -486,20 +488,67 @@ crate const DOC_RUST_LANG_ORG_CHANNEL: &str = env!("DOC_RUST_LANG_ORG_CHANNEL");
 /// Render a sequence of macro arms in a format suitable for displaying to the user
 /// as part of an item declaration.
 pub(super) fn render_macro_arms<'a>(
+    tcx: TyCtxt<'_>,
     matchers: impl Iterator<Item = &'a TokenTree>,
     arm_delim: &str,
 ) -> String {
     let mut out = String::new();
     for matcher in matchers {
-        writeln!(out, "    {} => {{ ... }}{}", render_macro_matcher(matcher), arm_delim).unwrap();
+        writeln!(out, "    {} => {{ ... }}{}", render_macro_matcher(tcx, matcher), arm_delim)
+            .unwrap();
     }
     out
 }
 
 /// Render a macro matcher in a format suitable for displaying to the user
 /// as part of an item declaration.
-pub(super) fn render_macro_matcher(matcher: &TokenTree) -> String {
-    rustc_ast_pretty::pprust::tt_to_string(matcher)
+pub(super) fn render_macro_matcher(tcx: TyCtxt<'_>, matcher: &TokenTree) -> String {
+    if let Some(snippet) = snippet_equal_to_token(tcx, matcher) {
+        snippet
+    } else {
+        rustc_ast_pretty::pprust::tt_to_string(matcher)
+    }
+}
+
+/// Find the source snippet for this token's Span, reparse it, and return the
+/// snippet if the reparsed TokenTree matches the argument TokenTree.
+fn snippet_equal_to_token(tcx: TyCtxt<'_>, matcher: &TokenTree) -> Option<String> {
+    // Find what rustc thinks is the source snippet.
+    // This may not actually be anything meaningful if this matcher was itself
+    // generated by a macro.
+    let source_map = tcx.sess.source_map();
+    let span = matcher.span();
+    let snippet = source_map.span_to_snippet(span).ok()?;
+
+    // Create a Parser.
+    let sess = ParseSess::new(FilePathMapping::empty());
+    let file_name = source_map.span_to_filename(span);
+    let mut parser =
+        match rustc_parse::maybe_new_parser_from_source_str(&sess, file_name, snippet.clone()) {
+            Ok(parser) => parser,
+            Err(diagnostics) => {
+                for mut diagnostic in diagnostics {
+                    diagnostic.cancel();
+                }
+                return None;
+            }
+        };
+
+    // Reparse a single token tree.
+    let mut reparsed_trees = match parser.parse_all_token_trees() {
+        Ok(reparsed_trees) => reparsed_trees,
+        Err(mut diagnostic) => {
+            diagnostic.cancel();
+            return None;
+        }
+    };
+    if reparsed_trees.len() != 1 {
+        return None;
+    }
+    let reparsed_tree = reparsed_trees.pop().unwrap();
+
+    // Compare against the original tree.
+    if reparsed_tree.eq_unspanned(matcher) { Some(snippet) } else { None }
 }
 
 pub(super) fn display_macro_source(
@@ -514,21 +563,21 @@ pub(super) fn display_macro_source(
     let matchers = tts.chunks(4).map(|arm| &arm[0]);
 
     if def.macro_rules {
-        format!("macro_rules! {} {{\n{}}}", name, render_macro_arms(matchers, ";"))
+        format!("macro_rules! {} {{\n{}}}", name, render_macro_arms(cx.tcx, matchers, ";"))
     } else {
         if matchers.len() <= 1 {
             format!(
                 "{}macro {}{} {{\n    ...\n}}",
                 vis.to_src_with_space(cx.tcx, def_id),
                 name,
-                matchers.map(render_macro_matcher).collect::<String>(),
+                matchers.map(|matcher| render_macro_matcher(cx.tcx, matcher)).collect::<String>(),
             )
         } else {
             format!(
                 "{}macro {} {{\n{}}}",
                 vis.to_src_with_space(cx.tcx, def_id),
                 name,
-                render_macro_arms(matchers, ","),
+                render_macro_arms(cx.tcx, matchers, ","),
             )
         }
     }
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index 11426cb6571..5431bd8565b 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -1126,18 +1126,27 @@ fn item_enum(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, e: &clean::Enum
             w.write_str("</h3>");
 
             use crate::clean::Variant;
-            if let Some((extra, fields)) = match *variant.kind {
-                clean::VariantItem(Variant::Struct(ref s)) => Some(("", &s.fields)),
-                clean::VariantItem(Variant::Tuple(ref fields)) => Some(("Tuple ", fields)),
+
+            let heading_and_fields = match &*variant.kind {
+                clean::VariantItem(Variant::Struct(s)) => Some(("Fields", &s.fields)),
+                // Documentation on tuple variant fields is rare, so to reduce noise we only emit
+                // the section if at least one field is documented.
+                clean::VariantItem(Variant::Tuple(fields))
+                    if fields.iter().any(|f| f.doc_value().is_some()) =>
+                {
+                    Some(("Tuple Fields", fields))
+                }
                 _ => None,
-            } {
+            };
+
+            if let Some((heading, fields)) = heading_and_fields {
                 let variant_id = cx.derive_id(format!(
                     "{}.{}.fields",
                     ItemType::Variant,
                     variant.name.as_ref().unwrap()
                 ));
                 write!(w, "<div class=\"sub-variant\" id=\"{id}\">", id = variant_id);
-                write!(w, "<h4>{extra}Fields</h4>", extra = extra,);
+                write!(w, "<h4>{heading}</h4>", heading = heading);
                 document_non_exhaustive(w, variant);
                 for field in fields {
                     match *field.kind {
diff --git a/src/test/run-make-fulldeps/coverage-reports/Makefile b/src/test/run-make-fulldeps/coverage-reports/Makefile
index 9122e0406c2..094d6b3ebf5 100644
--- a/src/test/run-make-fulldeps/coverage-reports/Makefile
+++ b/src/test/run-make-fulldeps/coverage-reports/Makefile
@@ -64,7 +64,7 @@ endif
 # if and when we allow `llvm-cov` to produce results for multiple files. Note, the path separators
 # appear to be normalized to `/` in those files, thankfully.)
 LLVM_COV_IGNORE_FILES=\
-	--ignore-filename-regex='(uses_crate.rs|uses_inline_crate.rs)'
+	--ignore-filename-regex='(uses_crate.rs|uses_inline_crate.rs|unused_mod.rs)'
 
 all: $(patsubst $(SOURCEDIR)/lib/%.rs,%,$(wildcard $(SOURCEDIR)/lib/*.rs)) $(patsubst $(SOURCEDIR)/%.rs,%,$(wildcard $(SOURCEDIR)/*.rs))
 
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.unused_mod.txt b/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.unused_mod.txt
new file mode 100644
index 00000000000..82d6fccc271
--- /dev/null
+++ b/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.unused_mod.txt
@@ -0,0 +1,4 @@
+    1|      0|pub fn never_called_function() {
+    2|      0|    println!("I am never called");
+    3|      0|}
+
diff --git a/src/test/run-make-fulldeps/coverage/lib/unused_mod_helper.rs b/src/test/run-make-fulldeps/coverage/lib/unused_mod_helper.rs
new file mode 100644
index 00000000000..ae1cc1531ed
--- /dev/null
+++ b/src/test/run-make-fulldeps/coverage/lib/unused_mod_helper.rs
@@ -0,0 +1,3 @@
+pub fn never_called_function() {
+    println!("I am never called");
+}
diff --git a/src/test/run-make-fulldeps/coverage/unused_mod.rs b/src/test/run-make-fulldeps/coverage/unused_mod.rs
new file mode 100644
index 00000000000..679b4e53188
--- /dev/null
+++ b/src/test/run-make-fulldeps/coverage/unused_mod.rs
@@ -0,0 +1,6 @@
+#[path = "lib/unused_mod_helper.rs"]
+mod unused_module;
+
+fn main() {
+    println!("hello world!");
+}
diff --git a/src/test/rustdoc/decl_macro.rs b/src/test/rustdoc/decl_macro.rs
index fe19dadbe02..94ade31b5e5 100644
--- a/src/test/rustdoc/decl_macro.rs
+++ b/src/test/rustdoc/decl_macro.rs
@@ -9,7 +9,7 @@ pub macro my_macro() {
 
 }
 
-// @has decl_macro/macro.my_macro_2.html //pre 'pub macro my_macro_2($($tok : tt) *) {'
+// @has decl_macro/macro.my_macro_2.html //pre 'pub macro my_macro_2($($tok:tt)*) {'
 // @has - //pre '...'
 // @has - //pre '}'
 pub macro my_macro_2($($tok:tt)*) {
@@ -18,8 +18,8 @@ pub macro my_macro_2($($tok:tt)*) {
 
 // @has decl_macro/macro.my_macro_multi.html //pre 'pub macro my_macro_multi {'
 // @has - //pre '(_) => { ... },'
-// @has - //pre '($foo : ident.$bar : expr) => { ... },'
-// @has - //pre '($($foo : literal), +) => { ... },'
+// @has - //pre '($foo:ident . $bar:expr) => { ... },'
+// @has - //pre '($($foo:literal),+) => { ... },'
 // @has - //pre '}'
 pub macro my_macro_multi {
     (_) => {
@@ -33,7 +33,7 @@ pub macro my_macro_multi {
     }
 }
 
-// @has decl_macro/macro.by_example_single.html //pre 'pub macro by_example_single($foo : expr) {'
+// @has decl_macro/macro.by_example_single.html //pre 'pub macro by_example_single($foo:expr) {'
 // @has - //pre '...'
 // @has - //pre '}'
 pub macro by_example_single {
@@ -42,12 +42,12 @@ pub macro by_example_single {
 
 mod a {
     mod b {
-        // @has decl_macro/a/b/macro.by_example_vis.html //pre 'pub(super) macro by_example_vis($foo : expr) {'
+        // @has decl_macro/a/b/macro.by_example_vis.html //pre 'pub(super) macro by_example_vis($foo:expr) {'
         pub(in super) macro by_example_vis {
             ($foo:expr) => {}
         }
         mod c {
-            // @has decl_macro/a/b/c/macro.by_example_vis_named.html //pre 'pub(in a) macro by_example_vis_named($foo : expr) {'
+            // @has decl_macro/a/b/c/macro.by_example_vis_named.html //pre 'pub(in a) macro by_example_vis_named($foo:expr) {'
             pub(in a) macro by_example_vis_named {
                 ($foo:expr) => {}
             }
diff --git a/src/test/rustdoc/issue-88600.rs b/src/test/rustdoc/issue-88600.rs
index 3761805b48b..fc63ed343bd 100644
--- a/src/test/rustdoc/issue-88600.rs
+++ b/src/test/rustdoc/issue-88600.rs
@@ -18,17 +18,18 @@ pub enum FooEnum {
     // @has - '//*[@id="variant.MixedHiddenFirst"]//code' 'MixedHiddenFirst(_, S)'
     // @count - '//*[@id="variant.MixedHiddenFirst.field.0"]' 0
     // @has - '//*[@id="variant.MixedHiddenFirst.field.1"]' '1: S'
-    MixedHiddenFirst(#[doc(hidden)] H, S),
+    MixedHiddenFirst(#[doc(hidden)] H, /** dox */ S),
     // @has - '//*[@id="variant.MixedHiddenLast"]//code' 'MixedHiddenLast(S, _)'
     // @has - '//*[@id="variant.MixedHiddenLast.field.0"]' '0: S'
     // @count - '//*[@id="variant.MixedHiddenLast.field.1"]' 0
-    MixedHiddenLast(S, #[doc(hidden)] H),
+    MixedHiddenLast(/** dox */ S, #[doc(hidden)] H),
     // @has - '//*[@id="variant.HiddenStruct"]//code' 'HiddenStruct'
     // @count - '//*[@id="variant.HiddenStruct.field.h"]' 0
     // @has - '//*[@id="variant.HiddenStruct.field.s"]' 's: S'
     HiddenStruct {
         #[doc(hidden)]
         h: H,
+        /// dox
         s: S,
     },
 }
diff --git a/src/test/rustdoc/macro-generated-macro.rs b/src/test/rustdoc/macro-generated-macro.rs
new file mode 100644
index 00000000000..25d8bc3ec62
--- /dev/null
+++ b/src/test/rustdoc/macro-generated-macro.rs
@@ -0,0 +1,14 @@
+macro_rules! outer {
+    ($($matcher:tt)*) => {
+        #[macro_export]
+        macro_rules! inner {
+            (<= $($matcher)* =>) => {};
+        }
+    }
+}
+
+// @has macro_generated_macro/macro.inner.html //pre 'macro_rules! inner {'
+// @has - //pre '(<= type $($i : ident) :: * + $e : expr =>) => { ... };'
+outer!(type $($i:ident)::* + $e:expr);
+
+inner!(<= type foo::bar + x.sort() =>);
diff --git a/src/test/rustdoc/macros.rs b/src/test/rustdoc/macros.rs
index 1cd454720e7..ae0cf7a1478 100644
--- a/src/test/rustdoc/macros.rs
+++ b/src/test/rustdoc/macros.rs
@@ -1,7 +1,7 @@
 // @has macros/macro.my_macro.html //pre 'macro_rules! my_macro {'
 // @has - //pre '() => { ... };'
-// @has - //pre '($a : tt) => { ... };'
-// @has - //pre '($e : expr) => { ... };'
+// @has - //pre '($a:tt) => { ... };'
+// @has - //pre '($e:expr) => { ... };'
 #[macro_export]
 macro_rules! my_macro {
     () => [];
@@ -12,8 +12,8 @@ macro_rules! my_macro {
 // Check that exported macro defined in a module are shown at crate root.
 // @has macros/macro.my_sub_macro.html //pre 'macro_rules! my_sub_macro {'
 // @has - //pre '() => { ... };'
-// @has - //pre '($a : tt) => { ... };'
-// @has - //pre '($e : expr) => { ... };'
+// @has - //pre '($a:tt) => { ... };'
+// @has - //pre '($e:expr) => { ... };'
 mod sub {
     #[macro_export]
     macro_rules! my_sub_macro {
diff --git a/src/test/rustdoc/reexports-priv.rs b/src/test/rustdoc/reexports-priv.rs
index 95f74180749..aea9b9f2b39 100644
--- a/src/test/rustdoc/reexports-priv.rs
+++ b/src/test/rustdoc/reexports-priv.rs
@@ -5,7 +5,7 @@
 
 extern crate reexports;
 
-// @has 'foo/macro.addr_of.html' '//*[@class="docblock item-decl"]' 'pub macro addr_of($place : expr) {'
+// @has 'foo/macro.addr_of.html' '//*[@class="docblock item-decl"]' 'pub macro addr_of($place:expr) {'
 pub use reexports::addr_of;
 // @!has 'foo/macro.addr_of_crate.html'
 pub(crate) use reexports::addr_of_crate;
@@ -61,11 +61,11 @@ use reexports::UnionLocal;
 
 pub mod outer {
     pub mod inner {
-        // @has 'foo/outer/inner/macro.addr_of.html' '//*[@class="docblock item-decl"]' 'pub macro addr_of($place : expr) {'
+        // @has 'foo/outer/inner/macro.addr_of.html' '//*[@class="docblock item-decl"]' 'pub macro addr_of($place:expr) {'
         pub use reexports::addr_of;
-        // @has 'foo/outer/inner/macro.addr_of_crate.html' '//*[@class="docblock item-decl"]' 'pub(crate) macro addr_of_crate($place : expr) {'
+        // @has 'foo/outer/inner/macro.addr_of_crate.html' '//*[@class="docblock item-decl"]' 'pub(crate) macro addr_of_crate($place:expr) {'
         pub(crate) use reexports::addr_of_crate;
-        // @has 'foo/outer/inner/macro.addr_of_super.html' '//*[@class="docblock item-decl"]' 'pub(in outer) macro addr_of_super($place : expr) {'
+        // @has 'foo/outer/inner/macro.addr_of_super.html' '//*[@class="docblock item-decl"]' 'pub(in outer) macro addr_of_super($place:expr) {'
         pub(super) use reexports::addr_of_super;
         // @!has 'foo/outer/inner/macro.addr_of_self.html'
         pub(self) use reexports::addr_of_self;
diff --git a/src/test/rustdoc/reexports.rs b/src/test/rustdoc/reexports.rs
index 3b315308470..7abcbfb6181 100644
--- a/src/test/rustdoc/reexports.rs
+++ b/src/test/rustdoc/reexports.rs
@@ -4,7 +4,7 @@
 
 extern crate reexports;
 
-// @has 'foo/macro.addr_of.html' '//*[@class="docblock item-decl"]' 'pub macro addr_of($place : expr) {'
+// @has 'foo/macro.addr_of.html' '//*[@class="docblock item-decl"]' 'pub macro addr_of($place:expr) {'
 pub use reexports::addr_of;
 // @!has 'foo/macro.addr_of_crate.html'
 pub(crate) use reexports::addr_of_crate;
@@ -60,7 +60,7 @@ use reexports::UnionLocal;
 
 pub mod outer {
     pub mod inner {
-        // @has 'foo/outer/inner/macro.addr_of.html' '//*[@class="docblock item-decl"]' 'pub macro addr_of($place : expr) {'
+        // @has 'foo/outer/inner/macro.addr_of.html' '//*[@class="docblock item-decl"]' 'pub macro addr_of($place:expr) {'
         pub use reexports::addr_of;
         // @!has 'foo/outer/inner/macro.addr_of_crate.html'
         pub(crate) use reexports::addr_of_crate;
diff --git a/src/test/rustdoc/tuple-struct-fields-doc.rs b/src/test/rustdoc/tuple-struct-fields-doc.rs
index 2e339fe8264..31426131bc2 100644
--- a/src/test/rustdoc/tuple-struct-fields-doc.rs
+++ b/src/test/rustdoc/tuple-struct-fields-doc.rs
@@ -24,6 +24,9 @@ pub struct Foo(
 // @has - '//*[@id="variant.BarVariant.field.0"]' '0: String'
 // @has - '//*[@id="variant.BarVariant.fields"]//*[@class="docblock"]' 'Hello docs'
 // @matches - '//*[@id="variant.FooVariant.fields"]/h4' '^Fields$'
+// @has - '//*[@id="variant.BazVariant.fields"]//*[@class="docblock"]' 'dox'
+// @has - '//*[@id="variant.OtherVariant.fields"]//*[@class="docblock"]' 'dox'
+// @!matches - '//*[@id="variant.QuuxVariant.fields"]/h4' '^Tuple Fields$'
 pub enum Bar {
     BarVariant(
         /// Hello docs
@@ -33,4 +36,15 @@ pub enum Bar {
        /// hello
        x: u32,
     },
+    BazVariant(
+        String,
+        /// dox
+        u32,
+    ),
+    OtherVariant(
+        /// dox
+        String,
+        u32,
+    ),
+    QuuxVariant(String),
 }
diff --git a/src/test/ui/type-alias-impl-trait/bound_reduction2.rs b/src/test/ui/type-alias-impl-trait/bound_reduction2.rs
index 579067340e8..cee8186dd8f 100644
--- a/src/test/ui/type-alias-impl-trait/bound_reduction2.rs
+++ b/src/test/ui/type-alias-impl-trait/bound_reduction2.rs
@@ -15,9 +15,5 @@ impl<W> Trait<W> for () {}
 
 fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
     //~^ ERROR non-defining opaque type use in defining scope
-    //~| ERROR non-defining opaque type use in defining scope
-    //~| ERROR non-defining opaque type use in defining scope
-    //~| ERROR `T` is part of concrete type but not used in parameter list
-    //~| ERROR `T` is part of concrete type but not used in parameter list
     ()
 }
diff --git a/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr b/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr
index a77c0000f12..03e696fe898 100644
--- a/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr
+++ b/src/test/ui/type-alias-impl-trait/bound_reduction2.stderr
@@ -1,34 +1,8 @@
-error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
-  --> $DIR/bound_reduction2.rs:16:60
-   |
-LL |   fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
-   |  ____________________________________________________________^
-LL | |
-LL | |
-LL | |
-...  |
-LL | |     ()
-LL | | }
-   | |_^
-
-error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
-  --> $DIR/bound_reduction2.rs:16:60
-   |
-LL |   fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
-   |  ____________________________________________________________^
-LL | |
-LL | |
-LL | |
-...  |
-LL | |     ()
-LL | | }
-   | |_^
-
 error: non-defining opaque type use in defining scope
-  --> $DIR/bound_reduction2.rs:16:1
+  --> $DIR/bound_reduction2.rs:16:46
    |
 LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                              ^^^^^^^^^^^^^
    |
 note: used non-generic type `<T as TraitWithAssoc>::Assoc` for generic parameter
   --> $DIR/bound_reduction2.rs:9:10
@@ -36,35 +10,11 @@ note: used non-generic type `<T as TraitWithAssoc>::Assoc` for generic parameter
 LL | type Foo<V> = impl Trait<V>;
    |          ^
 
-error: non-defining opaque type use in defining scope
-  --> $DIR/bound_reduction2.rs:16:1
-   |
-LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: used non-generic type `_` for generic parameter
-  --> $DIR/bound_reduction2.rs:9:10
-   |
-LL | type Foo<V> = impl Trait<V>;
-   |          ^
-
-error: non-defining opaque type use in defining scope
-  --> $DIR/bound_reduction2.rs:16:1
-   |
-LL | fn foo_desugared<T: TraitWithAssoc>(_: T) -> Foo<T::Assoc> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: used non-generic type `_` for generic parameter
-  --> $DIR/bound_reduction2.rs:9:10
-   |
-LL | type Foo<V> = impl Trait<V>;
-   |          ^
-
 error: could not find defining uses
   --> $DIR/bound_reduction2.rs:9:15
    |
 LL | type Foo<V> = impl Trait<V>;
    |               ^^^^^^^^^^^^^
 
-error: aborting due to 6 previous errors
+error: aborting due to 2 previous errors
 
diff --git a/src/tools/cargo b/src/tools/cargo
-Subproject 358e79fe56fe374649275ca7aebaafd57ade0e8
+Subproject 06b9d31743210b788b130c8a484c2838afa6fc2
diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index 4c28655bc86..9d2aa0f21c8 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -73,6 +73,7 @@ const RESTRICTED_DEPENDENCY_CRATES: &[&str] = &["rustc_driver", "rustc_codegen_l
 const PERMITTED_DEPENDENCIES: &[&str] = &[
     "addr2line",
     "adler",
+    "ahash",
     "aho-corasick",
     "annotate-snippets",
     "ansi_term",