Auto merge of #68831 - Dylan-DPC:rollup-j6x15y9, r=Dylan-DPC

Rollup of 7 pull requests

Successful merges:

 - #68282 (Instrument C / C++ in MemorySanitizer example)
 - #68758 (Fix 59191 - ICE when macro replaces crate root with non-module item)
 - #68805 (bootstrap: fix clippy warnings)
 - #68810 (Remove Copy impl from OnceWith)
 - #68815 (remove redundant imports (clippy::single_component_path_imports))
 - #68818 (fix couple of perf related clippy warnings)
 - #68819 (Suggest `split_at_mut` on multiple mutable index access)

Failed merges:

r? @ghost

52 files changed, 156 insertions, 114 deletions

diff --git a/src/bootstrap/bin/rustc.rs b/src/bootstrap/bin/rustc.rs
index a34ec44566b..a8c00c8c3ca 100644
--- a/src/bootstrap/bin/rustc.rs
+++ b/src/bootstrap/bin/rustc.rs
@@ -47,7 +47,7 @@ fn main() {
     };
     let stage = env::var("RUSTC_STAGE").expect("RUSTC_STAGE was not set");
     let sysroot = env::var_os("RUSTC_SYSROOT").expect("RUSTC_SYSROOT was not set");
-    let on_fail = env::var_os("RUSTC_ON_FAIL").map(|of| Command::new(of));
+    let on_fail = env::var_os("RUSTC_ON_FAIL").map(Command::new);
 
     let rustc = env::var_os(rustc).unwrap_or_else(|| panic!("{:?} was not set", rustc));
     let libdir = env::var_os(libdir).unwrap_or_else(|| panic!("{:?} was not set", libdir));
@@ -64,7 +64,7 @@ fn main() {
     if let Some(crate_name) = crate_name {
         if let Some(target) = env::var_os("RUSTC_TIME") {
             if target == "all"
-                || target.into_string().unwrap().split(",").any(|c| c.trim() == crate_name)
+                || target.into_string().unwrap().split(',').any(|c| c.trim() == crate_name)
             {
                 cmd.arg("-Ztime");
             }
@@ -189,7 +189,7 @@ fn main() {
                 crate_name,
                 is_test,
                 dur.as_secs(),
-                dur.subsec_nanos() / 1_000_000
+                dur.subsec_millis()
             );
 
             match status.code() {
diff --git a/src/bootstrap/bin/rustdoc.rs b/src/bootstrap/bin/rustdoc.rs
index 8c8b33a4e4e..04345867bf5 100644
--- a/src/bootstrap/bin/rustdoc.rs
+++ b/src/bootstrap/bin/rustdoc.rs
@@ -61,7 +61,7 @@ fn main() {
     }
 
     // Needed to be able to run all rustdoc tests.
-    if let Some(_) = env::var_os("RUSTDOC_GENERATE_REDIRECT_PAGES") {
+    if env::var_os("RUSTDOC_GENERATE_REDIRECT_PAGES").is_some() {
         // This "unstable-options" can be removed when `--generate-redirect-pages` is stabilized
         if !has_unstable {
             cmd.arg("-Z").arg("unstable-options");
diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index d9c894aa9c6..18f6fda7608 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -510,7 +510,7 @@ impl<'a> Builder<'a> {
             Subcommand::Format { .. } | Subcommand::Clean { .. } => panic!(),
         };
 
-        let builder = Builder {
+        Builder {
             build,
             top_stage: build.config.stage.unwrap_or(2),
             kind,
@@ -518,9 +518,7 @@ impl<'a> Builder<'a> {
             stack: RefCell::new(Vec::new()),
             time_spent_on_dependencies: Cell::new(Duration::new(0, 0)),
             paths: paths.to_owned(),
-        };
-
-        builder
+        }
     }
 
     pub fn execute_cli(&self) {
@@ -753,13 +751,12 @@ impl<'a> Builder<'a> {
             cargo.env("RUST_CHECK", "1");
         }
 
-        let stage;
-        if compiler.stage == 0 && self.local_rebuild {
+        let stage = if compiler.stage == 0 && self.local_rebuild {
             // Assume the local-rebuild rustc already has stage1 features.
-            stage = 1;
+            1
         } else {
-            stage = compiler.stage;
-        }
+            compiler.stage
+        };
 
         let mut rustflags = Rustflags::new(&target);
         if stage != 0 {
@@ -1252,12 +1249,7 @@ impl<'a> Builder<'a> {
         };
 
         if self.config.print_step_timings && dur > Duration::from_millis(100) {
-            println!(
-                "[TIMING] {:?} -- {}.{:03}",
-                step,
-                dur.as_secs(),
-                dur.subsec_nanos() / 1_000_000
-            );
+            println!("[TIMING] {:?} -- {}.{:03}", step, dur.as_secs(), dur.subsec_millis());
         }
 
         {
@@ -1302,7 +1294,7 @@ impl Rustflags {
 
     fn arg(&mut self, arg: &str) -> &mut Self {
         assert_eq!(arg.split_whitespace().count(), 1);
-        if self.0.len() > 0 {
+        if !self.0.is_empty() {
             self.0.push_str(" ");
         }
         self.0.push_str(arg);
diff --git a/src/bootstrap/builder/tests.rs b/src/bootstrap/builder/tests.rs
index 5fefb972866..cca8ab80c93 100644
--- a/src/bootstrap/builder/tests.rs
+++ b/src/bootstrap/builder/tests.rs
@@ -19,7 +19,6 @@ fn configure(host: &[&str], target: &[&str]) -> Config {
     config.out = dir;
     config.build = INTERNER.intern_str("A");
     config.hosts = vec![config.build]
-        .clone()
         .into_iter()
         .chain(host.iter().map(|s| INTERNER.intern_str(s)))
         .collect::<Vec<_>>();
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index eced03506ab..7dded96e18e 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -18,7 +18,6 @@ use std::str;
 use build_helper::{output, t, up_to_date};
 use filetime::FileTime;
 use serde::Deserialize;
-use serde_json;
 
 use crate::builder::Cargo;
 use crate::dist;
@@ -149,7 +148,8 @@ fn copy_third_party_objects(
     // which is provided by std for this target.
     if target == "x86_64-fortanix-unknown-sgx" {
         let src_path_env = "X86_FORTANIX_SGX_LIBS";
-        let src = env::var(src_path_env).expect(&format!("{} not found in env", src_path_env));
+        let src =
+            env::var(src_path_env).unwrap_or_else(|_| panic!("{} not found in env", src_path_env));
         copy_and_stamp(Path::new(&src), "libunwind.a");
     }
 
@@ -361,7 +361,7 @@ impl Step for StartupObjects {
                 );
             }
 
-            let target = sysroot_dir.join(file.to_string() + ".o");
+            let target = sysroot_dir.join((*file).to_string() + ".o");
             builder.copy(dst_file, &target);
             target_deps.push(target);
         }
@@ -515,7 +515,7 @@ pub fn rustc_cargo_env(builder: &Builder<'_>, cargo: &mut Cargo, target: Interne
         .env("CFG_VERSION", builder.rust_version())
         .env("CFG_PREFIX", builder.config.prefix.clone().unwrap_or_default());
 
-    let libdir_relative = builder.config.libdir_relative().unwrap_or(Path::new("lib"));
+    let libdir_relative = builder.config.libdir_relative().unwrap_or_else(|| Path::new("lib"));
     cargo.env("CFG_LIBDIR_RELATIVE", libdir_relative);
 
     if let Some(ref ver_date) = builder.rust_info.commit_date() {
@@ -843,11 +843,11 @@ pub fn run_cargo(
         };
         for filename in filenames {
             // Skip files like executables
-            if !filename.ends_with(".rlib")
-                && !filename.ends_with(".lib")
-                && !filename.ends_with(".a")
-                && !is_dylib(&filename)
-                && !(is_check && filename.ends_with(".rmeta"))
+            if !(filename.ends_with(".rlib")
+                || filename.ends_with(".lib")
+                || filename.ends_with(".a")
+                || is_dylib(&filename)
+                || (is_check && filename.ends_with(".rmeta")))
             {
                 continue;
             }
@@ -905,7 +905,7 @@ pub fn run_cargo(
     for (prefix, extension, expected_len) in toplevel {
         let candidates = contents.iter().filter(|&&(_, ref filename, ref meta)| {
             filename.starts_with(&prefix[..])
-                && filename[prefix.len()..].starts_with("-")
+                && filename[prefix.len()..].starts_with('-')
                 && filename.ends_with(&extension[..])
                 && meta.len() == expected_len
         });
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 110c8b844d5..709cf2908ea 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -16,7 +16,6 @@ use crate::flags::Flags;
 pub use crate::flags::Subcommand;
 use build_helper::t;
 use serde::Deserialize;
-use toml;
 
 /// Global configuration for the entire build and/or bootstrap.
 ///
@@ -440,7 +439,7 @@ impl Config {
                     }
                 }
             })
-            .unwrap_or_else(|| TomlConfig::default());
+            .unwrap_or_else(TomlConfig::default);
 
         let build = toml.build.clone().unwrap_or_default();
         // set by bootstrap.py
@@ -539,7 +538,7 @@ impl Config {
             config.llvm_ldflags = llvm.ldflags.clone();
             set(&mut config.llvm_use_libcxx, llvm.use_libcxx);
             config.llvm_use_linker = llvm.use_linker.clone();
-            config.llvm_allow_old_toolchain = llvm.allow_old_toolchain.clone();
+            config.llvm_allow_old_toolchain = llvm.allow_old_toolchain;
         }
 
         if let Some(ref rust) = toml.rust {
@@ -606,7 +605,7 @@ impl Config {
                 target.ar = cfg.ar.clone().map(PathBuf::from);
                 target.ranlib = cfg.ranlib.clone().map(PathBuf::from);
                 target.linker = cfg.linker.clone().map(PathBuf::from);
-                target.crt_static = cfg.crt_static.clone();
+                target.crt_static = cfg.crt_static;
                 target.musl_root = cfg.musl_root.clone().map(PathBuf::from);
                 target.wasi_root = cfg.wasi_root.clone().map(PathBuf::from);
                 target.qemu_rootfs = cfg.qemu_rootfs.clone().map(PathBuf::from);
diff --git a/src/bootstrap/dist.rs b/src/bootstrap/dist.rs
index facf816857f..8003d8906e8 100644
--- a/src/bootstrap/dist.rs
+++ b/src/bootstrap/dist.rs
@@ -828,7 +828,7 @@ impl Step for Analysis {
         assert!(builder.config.extended);
         let name = pkgname(builder, "rust-analysis");
 
-        if &compiler.host != builder.config.build {
+        if compiler.host != builder.config.build {
             return distdir(builder).join(format!("{}-{}.tar.gz", name, target));
         }
 
@@ -877,7 +877,7 @@ fn copy_src_dirs(builder: &Builder<'_>, src_dirs: &[&str], exclude_dirs: &[&str]
             Some(path) => path,
             None => return false,
         };
-        if spath.ends_with("~") || spath.ends_with(".pyc") {
+        if spath.ends_with('~') || spath.ends_with(".pyc") {
             return false;
         }
 
diff --git a/src/bootstrap/doc.rs b/src/bootstrap/doc.rs
index 204056598d9..b0d9a5b9464 100644
--- a/src/bootstrap/doc.rs
+++ b/src/bootstrap/doc.rs
@@ -560,7 +560,7 @@ impl Step for Rustdoc {
         builder.ensure(Rustc { stage, target });
 
         // Build rustdoc.
-        builder.ensure(tool::Rustdoc { compiler: compiler });
+        builder.ensure(tool::Rustdoc { compiler });
 
         // Symlink compiler docs to the output directory of rustdoc documentation.
         let out_dir = builder.stage_out(compiler, Mode::ToolRustc).join(target).join("doc");
diff --git a/src/bootstrap/flags.rs b/src/bootstrap/flags.rs
index 2101ef27f9d..516be6a30c2 100644
--- a/src/bootstrap/flags.rs
+++ b/src/bootstrap/flags.rs
@@ -571,7 +571,7 @@ fn split(s: &[String]) -> Vec<String> {
 }
 
 fn parse_deny_warnings(matches: &getopts::Matches) -> Option<bool> {
-    match matches.opt_str("warnings").as_ref().map(|v| v.as_str()) {
+    match matches.opt_str("warnings").as_deref() {
         Some("deny") => Some(true),
         Some("warn") => Some(false),
         Some(value) => {
diff --git a/src/bootstrap/install.rs b/src/bootstrap/install.rs
index f8734ebdf42..6549262811b 100644
--- a/src/bootstrap/install.rs
+++ b/src/bootstrap/install.rs
@@ -126,9 +126,8 @@ fn add_destdir(path: &Path, destdir: &Option<PathBuf>) -> PathBuf {
         None => return path.to_path_buf(),
     };
     for part in path.components() {
-        match part {
-            Component::Normal(s) => ret.push(s),
-            _ => {}
+        if let Component::Normal(s) = part {
+            ret.push(s)
         }
     }
     ret
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 637323331f5..0db4fb38901 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -444,7 +444,7 @@ impl Build {
             builder.execute_cli();
         } else {
             let builder = builder::Builder::new(&self);
-            let _ = builder.execute_cli();
+            builder.execute_cli();
         }
 
         // Check for postponed failures from `test --no-fail-fast`.
@@ -839,7 +839,7 @@ impl Build {
             .target_config
             .get(&target)
             .and_then(|t| t.musl_root.as_ref())
-            .or(self.config.musl_root.as_ref())
+            .or_else(|| self.config.musl_root.as_ref())
             .map(|p| &**p)
     }
 
diff --git a/src/bootstrap/metadata.rs b/src/bootstrap/metadata.rs
index 8a26adc7ed5..292aa3b1e24 100644
--- a/src/bootstrap/metadata.rs
+++ b/src/bootstrap/metadata.rs
@@ -5,7 +5,6 @@ use std::process::Command;
 
 use build_helper::output;
 use serde::Deserialize;
-use serde_json;
 
 use crate::cache::INTERNER;
 use crate::{Build, Crate};
diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 5bbd9f47fc9..1cfb4b2f63b 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -15,8 +15,6 @@ use std::path::{Path, PathBuf};
 use std::process::Command;
 
 use build_helper::{output, t};
-use cc;
-use cmake;
 
 use crate::builder::{Builder, RunConfig, ShouldRun, Step};
 use crate::cache::Interned;
@@ -205,7 +203,7 @@ impl Step for Llvm {
             cfg.define("LLVM_ENABLE_LIBXML2", "OFF");
         }
 
-        if enabled_llvm_projects.len() > 0 {
+        if !enabled_llvm_projects.is_empty() {
             enabled_llvm_projects.sort();
             enabled_llvm_projects.dedup();
             cfg.define("LLVM_ENABLE_PROJECTS", enabled_llvm_projects.join(";"));
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 6adf9ddaf34..8d9e6201001 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1424,13 +1424,10 @@ impl Step for ErrorIndex {
 }
 
 fn markdown_test(builder: &Builder<'_>, compiler: Compiler, markdown: &Path) -> bool {
-    match fs::read_to_string(markdown) {
-        Ok(contents) => {
-            if !contents.contains("```") {
-                return true;
-            }
+    if let Ok(contents) = fs::read_to_string(markdown) {
+        if !contents.contains("```") {
+            return true;
         }
-        Err(_) => {}
     }
 
     builder.info(&format!("doc tests for: {}", markdown.display()));
diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 7f24768a4f1..67e0ed5c580 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -234,7 +234,7 @@ pub fn prepare_tool_cargo(
         cargo.env("RUSTC_EXTERNAL_TOOL", "1");
     }
 
-    let mut features = extra_features.iter().cloned().collect::<Vec<_>>();
+    let mut features = extra_features.to_vec();
     if builder.build.config.cargo_native_static {
         if path.ends_with("cargo")
             || path.ends_with("rls")
diff --git a/src/bootstrap/toolstate.rs b/src/bootstrap/toolstate.rs
index b068c8200ac..bb012a38855 100644
--- a/src/bootstrap/toolstate.rs
+++ b/src/bootstrap/toolstate.rs
@@ -124,7 +124,7 @@ fn check_changed_files(toolstates: &HashMap<Box<str>, ToolState>) {
     let output = t!(String::from_utf8(output.stdout));
 
     for (tool, submodule) in STABLE_TOOLS.iter().chain(NIGHTLY_TOOLS.iter()) {
-        let changed = output.lines().any(|l| l.starts_with("M") && l.ends_with(submodule));
+        let changed = output.lines().any(|l| l.starts_with('M') && l.ends_with(submodule));
         eprintln!("Verifying status of {}...", tool);
         if !changed {
             continue;
diff --git a/src/bootstrap/util.rs b/src/bootstrap/util.rs
index 7d1efe4610f..eac790fe504 100644
--- a/src/bootstrap/util.rs
+++ b/src/bootstrap/util.rs
@@ -98,7 +98,7 @@ impl Drop for TimeIt {
     fn drop(&mut self) {
         let time = self.1.elapsed();
         if !self.0 {
-            println!("\tfinished in {}.{:03}", time.as_secs(), time.subsec_nanos() / 1_000_000);
+            println!("\tfinished in {}.{:03}", time.as_secs(), time.subsec_millis());
         }
     }
 }
diff --git a/src/doc/unstable-book/src/compiler-flags/sanitizer.md b/src/doc/unstable-book/src/compiler-flags/sanitizer.md
index 64bff2a6fe0..414ac7e63a3 100644
--- a/src/doc/unstable-book/src/compiler-flags/sanitizer.md
+++ b/src/doc/unstable-book/src/compiler-flags/sanitizer.md
@@ -170,7 +170,7 @@ Shadow byte legend (one shadow byte represents 8 application bytes):
 ## MemorySanitizer
 
 Use of uninitialized memory. Note that we are using `-Zbuild-std` to instrument
-standard library, and passing `-msan-track-origins=2` to the LLVM to track
+the standard library, and passing `-Zsanitizer-track-origins` to track the
 origins of uninitialized memory:
 
 ```shell
@@ -185,7 +185,15 @@ fn main() {
     }
 }
 
-$ env RUSTFLAGS="-Zsanitizer=memory -Cllvm-args=-msan-track-origins=2" cargo -Zbuild-std run --target x86_64-unknown-linux-gnu
+$ export \
+  CC=clang \
+  CXX=clang++ \
+  CFLAGS='-fsanitize=memory -fsanitize-memory-track-origins' \
+  CXXFLAGS='-fsanitize=memory -fsanitize-memory-track-origins' \
+  RUSTFLAGS='-Zsanitizer=memory -Zsanitizer-memory-track-origins' \
+  RUSTDOCFLAGS='-Zsanitizer=memory -Zsanitizer-memory-track-origins'
+$ cargo clean
+$ cargo -Zbuild-std run --target x86_64-unknown-linux-gnu
 ==9416==WARNING: MemorySanitizer: use-of-uninitialized-value
     #0 0x560c04f7488a in core::fmt::num::imp::fmt_u64::haa293b0b098501ca $RUST/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/src/libcore/fmt/num.rs:202:16
 ...
diff --git a/src/libcore/iter/sources.rs b/src/libcore/iter/sources.rs
index 5a31acab273..a1d4e1b31e9 100644
--- a/src/libcore/iter/sources.rs
+++ b/src/libcore/iter/sources.rs
@@ -398,7 +398,7 @@ pub fn once<T>(value: T) -> Once<T> {
 /// See its documentation for more.
 ///
 /// [`once_with`]: fn.once_with.html
-#[derive(Copy, Clone, Debug)]
+#[derive(Clone, Debug)]
 #[stable(feature = "iter_once_with", since = "1.43.0")]
 pub struct OnceWith<F> {
     gen: Option<F>,
diff --git a/src/librustc/traits/mod.rs b/src/librustc/traits/mod.rs
index daaba95cf6b..b1b3d44044e 100644
--- a/src/librustc/traits/mod.rs
+++ b/src/librustc/traits/mod.rs
@@ -31,7 +31,6 @@ use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use crate::ty::subst::{InternalSubsts, SubstsRef};
 use crate::ty::{self, AdtKind, GenericParamDefKind, List, ToPredicate, Ty, TyCtxt, WithConstness};
 use crate::util::common::ErrorReported;
-use chalk_engine;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_macros::HashStable;
diff --git a/src/librustc/traits/structural_impls.rs b/src/librustc/traits/structural_impls.rs
index 58204a460d7..1db83c5bafa 100644
--- a/src/librustc/traits/structural_impls.rs
+++ b/src/librustc/traits/structural_impls.rs
@@ -2,7 +2,6 @@ use crate::traits;
 use crate::traits::project::Normalized;
 use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use crate::ty::{self, Lift, Ty, TyCtxt};
-use chalk_engine;
 use rustc_span::symbol::Symbol;
 use smallvec::SmallVec;
 
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index fe25f451a3a..1b3e42447c4 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -46,7 +46,6 @@ use rustc_target::abi::Align;
 use syntax::ast::{self, Constness, Ident, Name};
 use syntax::node_id::{NodeId, NodeMap, NodeSet};
 
-use smallvec;
 use std::cell::RefCell;
 use std::cmp::{self, Ordering};
 use std::fmt;
@@ -1348,7 +1347,7 @@ pub trait ToPredicate<'tcx> {
 impl<'tcx> ToPredicate<'tcx> for ConstnessAnd<TraitRef<'tcx>> {
     fn to_predicate(&self) -> Predicate<'tcx> {
         ty::Predicate::Trait(
-            ty::Binder::dummy(ty::TraitPredicate { trait_ref: self.value.clone() }),
+            ty::Binder::dummy(ty::TraitPredicate { trait_ref: self.value }),
             self.constness,
         )
     }
diff --git a/src/librustc_builtin_macros/log_syntax.rs b/src/librustc_builtin_macros/log_syntax.rs
index 6d9bfbfd05f..ac7ba49ba18 100644
--- a/src/librustc_builtin_macros/log_syntax.rs
+++ b/src/librustc_builtin_macros/log_syntax.rs
@@ -1,6 +1,5 @@
 use rustc_ast_pretty::pprust;
 use rustc_expand::base;
-use rustc_span;
 use syntax::tokenstream::TokenStream;
 
 pub fn expand_log_syntax<'cx>(
diff --git a/src/librustc_expand/expand.rs b/src/librustc_expand/expand.rs
index f08bed57315..0b8cbd3a783 100644
--- a/src/librustc_expand/expand.rs
+++ b/src/librustc_expand/expand.rs
@@ -363,7 +363,17 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 krate.attrs = vec![];
                 krate.module = ast::Mod { inner: orig_mod_span, items: vec![], inline: true };
             }
-            _ => unreachable!(),
+            Some(ast::Item { span, kind, .. }) => {
+                krate.attrs = vec![];
+                krate.module = ast::Mod { inner: orig_mod_span, items: vec![], inline: true };
+                self.cx.span_err(
+                    span,
+                    &format!(
+                        "expected crate top-level item to be a module after macro expansion, found a {}",
+                        kind.descriptive_variant()
+                    ),
+                );
+            }
         };
         self.cx.trace_macros_diag();
         krate
diff --git a/src/librustc_incremental/persist/file_format.rs b/src/librustc_incremental/persist/file_format.rs
index 7534b7e9ef4..5c72b049d97 100644
--- a/src/librustc_incremental/persist/file_format.rs
+++ b/src/librustc_incremental/persist/file_format.rs
@@ -90,8 +90,7 @@ pub fn read_file(
         let mut rustc_version_str_len = [0u8; 1];
         file.read_exact(&mut rustc_version_str_len)?;
         let rustc_version_str_len = rustc_version_str_len[0] as usize;
-        let mut buffer = Vec::with_capacity(rustc_version_str_len);
-        buffer.resize(rustc_version_str_len, 0);
+        let mut buffer = vec![0; rustc_version_str_len];
         file.read_exact(&mut buffer)?;
 
         if buffer != rustc_version().as_bytes() {
diff --git a/src/librustc_interface/callbacks.rs b/src/librustc_interface/callbacks.rs
index eb9c118bb01..803e8958572 100644
--- a/src/librustc_interface/callbacks.rs
+++ b/src/librustc_interface/callbacks.rs
@@ -11,7 +11,6 @@
 
 use rustc::ty::tls;
 use rustc_errors::{Diagnostic, TRACK_DIAGNOSTICS};
-use rustc_span;
 use std::fmt;
 
 /// This is a callback from libsyntax as it cannot access the implicit state
diff --git a/src/librustc_interface/passes.rs b/src/librustc_interface/passes.rs
index 0be73e55e9c..bf8bcd71efa 100644
--- a/src/librustc_interface/passes.rs
+++ b/src/librustc_interface/passes.rs
@@ -17,7 +17,6 @@ use rustc::traits;
 use rustc::ty::steal::Steal;
 use rustc::ty::{self, GlobalCtxt, ResolverOutputs, TyCtxt};
 use rustc::util::common::ErrorReported;
-use rustc_builtin_macros;
 use rustc_codegen_ssa::back::link::emit_metadata;
 use rustc_codegen_utils::codegen_backend::CodegenBackend;
 use rustc_codegen_utils::link::filename_for_metadata;
@@ -26,18 +25,15 @@ use rustc_data_structures::{box_region_allow_access, declare_box_region_type, pa
 use rustc_errors::PResult;
 use rustc_expand::base::ExtCtxt;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
-use rustc_incremental;
 use rustc_lint::LintStore;
 use rustc_mir as mir;
 use rustc_mir_build as mir_build;
 use rustc_parse::{parse_crate_from_file, parse_crate_from_source_str};
 use rustc_passes::{self, hir_stats, layout_test};
 use rustc_plugin_impl as plugin;
-use rustc_privacy;
 use rustc_resolve::{Resolver, ResolverArenas};
 use rustc_span::symbol::Symbol;
 use rustc_span::FileName;
-use rustc_traits;
 use rustc_typeck as typeck;
 use syntax::mut_visit::MutVisitor;
 use syntax::{self, ast, visit};
diff --git a/src/librustc_macros/src/lift.rs b/src/librustc_macros/src/lift.rs
index 1b91fc5018a..a246b34b2c2 100644
--- a/src/librustc_macros/src/lift.rs
+++ b/src/librustc_macros/src/lift.rs
@@ -1,7 +1,5 @@
-use proc_macro2;
 use quote::quote;
 use syn::{self, parse_quote};
-use synstructure;
 
 pub fn lift_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     s.add_bounds(synstructure::AddBounds::Generics);
diff --git a/src/librustc_macros/src/query.rs b/src/librustc_macros/src/query.rs
index f680b0d64cd..6dc4f7f2515 100644
--- a/src/librustc_macros/src/query.rs
+++ b/src/librustc_macros/src/query.rs
@@ -2,7 +2,6 @@ use itertools::Itertools;
 use proc_macro::TokenStream;
 use proc_macro2::{Delimiter, TokenTree};
 use quote::quote;
-use syn;
 use syn::parse::{Parse, ParseStream, Result};
 use syn::punctuated::Punctuated;
 use syn::spanned::Spanned;
diff --git a/src/librustc_macros/src/symbols.rs b/src/librustc_macros/src/symbols.rs
index c692c7f3995..feddcd5f994 100644
--- a/src/librustc_macros/src/symbols.rs
+++ b/src/librustc_macros/src/symbols.rs
@@ -1,7 +1,6 @@
 use proc_macro::TokenStream;
 use quote::quote;
 use std::collections::HashSet;
-use syn;
 use syn::parse::{Parse, ParseStream, Result};
 use syn::{braced, parse_macro_input, Ident, LitStr, Token};
 
diff --git a/src/librustc_macros/src/type_foldable.rs b/src/librustc_macros/src/type_foldable.rs
index 3d58984a900..687401e3344 100644
--- a/src/librustc_macros/src/type_foldable.rs
+++ b/src/librustc_macros/src/type_foldable.rs
@@ -1,6 +1,4 @@
 use quote::quote;
-use syn;
-use synstructure;
 
 pub fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     if let syn::Data::Union(_) = s.ast().data {
diff --git a/src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs b/src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs
index b0b9790abb1..b49e7b7f0d9 100644
--- a/src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs
+++ b/src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs
@@ -397,14 +397,20 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
             (BorrowKind::Mut { .. }, BorrowKind::Mut { .. }) => {
                 first_borrow_desc = "first ";
-                self.cannot_mutably_borrow_multiply(
+                let mut err = self.cannot_mutably_borrow_multiply(
                     span,
                     &desc_place,
                     &msg_place,
                     issued_span,
                     &msg_borrow,
                     None,
-                )
+                );
+                self.suggest_split_at_mut_if_applicable(
+                    &mut err,
+                    &place,
+                    &issued_borrow.borrowed_place,
+                );
+                err
             }
 
             (BorrowKind::Unique, BorrowKind::Unique) => {
@@ -549,6 +555,23 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         err
     }
 
+    fn suggest_split_at_mut_if_applicable(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        place: &Place<'tcx>,
+        borrowed_place: &Place<'tcx>,
+    ) {
+        match (&place.projection[..], &borrowed_place.projection[..]) {
+            ([ProjectionElem::Index(_)], [ProjectionElem::Index(_)]) => {
+                err.help(
+                    "consider using `.split_at_mut(position)` or similar method to obtain \
+                     two mutable non-overlapping sub-slices",
+                );
+            }
+            _ => {}
+        }
+    }
+
     /// Returns the description of the root place for a conflicting borrow and the full
     /// descriptions of the places that caused the conflict.
     ///
diff --git a/src/librustc_passes/dead.rs b/src/librustc_passes/dead.rs
index 2ff9d744f2c..9367909d10c 100644
--- a/src/librustc_passes/dead.rs
+++ b/src/librustc_passes/dead.rs
@@ -15,7 +15,6 @@ use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::{Node, PatKind, TyKind};
 use rustc_session::lint;
 
-use rustc_span;
 use rustc_span::symbol::sym;
 use syntax::{ast, attr};
 
diff --git a/src/librustc_session/config.rs b/src/librustc_session/config.rs
index 813d14d616d..ad1a6c4906e 100644
--- a/src/librustc_session/config.rs
+++ b/src/librustc_session/config.rs
@@ -22,8 +22,6 @@ use rustc_span::symbol::{sym, Symbol};
 use rustc_errors::emitter::HumanReadableErrorType;
 use rustc_errors::{ColorConfig, FatalError, Handler, HandlerFlags};
 
-use getopts;
-
 use std::collections::btree_map::{
     Iter as BTreeMapIter, Keys as BTreeMapKeysIter, Values as BTreeMapValuesIter,
 };
@@ -816,7 +814,6 @@ mod opt {
     #![allow(dead_code)]
 
     use super::RustcOptGroup;
-    use getopts;
 
     pub type R = RustcOptGroup;
     pub type S = &'static str;
@@ -1862,7 +1859,6 @@ pub fn parse_crate_types_from_list(list_list: Vec<String>) -> Result<Vec<CrateTy
 pub mod nightly_options {
     use super::{ErrorOutputType, OptionStability, RustcOptGroup};
     use crate::early_error;
-    use getopts;
     use rustc_feature::UnstableFeatures;
 
     pub fn is_unstable_enabled(matches: &getopts::Matches) -> bool {
diff --git a/src/librustc_session/options.rs b/src/librustc_session/options.rs
index be0e668a467..d6b71641da5 100644
--- a/src/librustc_session/options.rs
+++ b/src/librustc_session/options.rs
@@ -11,8 +11,6 @@ use rustc_target::spec::{LinkerFlavor, MergeFunctions, PanicStrategy, RelroLevel
 use rustc_feature::UnstableFeatures;
 use rustc_span::edition::Edition;
 
-use getopts;
-
 use std::collections::BTreeMap;
 
 use std::collections::hash_map::DefaultHasher;
diff --git a/src/librustc_session/session.rs b/src/librustc_session/session.rs
index a40d6451b95..f8cba58f9d9 100644
--- a/src/librustc_session/session.rs
+++ b/src/librustc_session/session.rs
@@ -33,7 +33,6 @@ use rustc_data_structures::jobserver::{self, Client};
 use rustc_data_structures::profiling::{SelfProfiler, SelfProfilerRef};
 use rustc_target::spec::{PanicStrategy, RelroLevel, Target, TargetTriple};
 
-use std;
 use std::cell::{self, RefCell};
 use std::env;
 use std::fmt;
diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index c2123876b67..231aed48fb6 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -1438,10 +1438,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         // Expand trait aliases recursively and check that only one regular (non-auto) trait
         // is used and no 'maybe' bounds are used.
-        let expanded_traits = traits::expand_trait_aliases(
-            tcx,
-            bounds.trait_bounds.iter().map(|&(a, b, _)| (a.clone(), b)),
-        );
+        let expanded_traits =
+            traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
         let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
             expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
         if regular_traits.len() > 1 {
diff --git a/src/librustc_typeck/variance/mod.rs b/src/librustc_typeck/variance/mod.rs
index 27dc03bbbe2..32bd7e4c4c1 100644
--- a/src/librustc_typeck/variance/mod.rs
+++ b/src/librustc_typeck/variance/mod.rs
@@ -3,7 +3,6 @@
 //!
 //! [rustc guide]: https://rust-lang.github.io/rustc-guide/variance.html
 
-use arena;
 use hir::Node;
 use rustc::ty::query::Providers;
 use rustc::ty::{self, CrateVariancesMap, TyCtxt};
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index e110545c6f2..356660763a7 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -16,7 +16,6 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
-use rustc_span;
 use rustc_span::symbol::{kw, sym, Symbol};
 use std::mem;
 
diff --git a/src/librustdoc/config.rs b/src/librustdoc/config.rs
index 22f5d0dc2c0..1b776930d7a 100644
--- a/src/librustdoc/config.rs
+++ b/src/librustdoc/config.rs
@@ -3,7 +3,6 @@ use std::ffi::OsStr;
 use std::fmt;
 use std::path::PathBuf;
 
-use getopts;
 use rustc::lint::Level;
 use rustc::session;
 use rustc::session::config::{
@@ -13,7 +12,6 @@ use rustc::session::config::{
 use rustc::session::config::{parse_crate_types_from_list, parse_externs, CrateType};
 use rustc::session::config::{CodegenOptions, DebuggingOptions, ErrorOutputType, Externs};
 use rustc::session::search_paths::SearchPath;
-use rustc_driver;
 use rustc_span::edition::{Edition, DEFAULT_EDITION};
 use rustc_target::spec::TargetTriple;
 
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index a8baa89c6f1..429988db9d8 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -11,7 +11,6 @@ use rustc_hir::def::Namespace::TypeNS;
 use rustc_hir::def_id::{CrateNum, DefId, DefIndex, LOCAL_CRATE};
 use rustc_hir::HirId;
 use rustc_interface::interface;
-use rustc_lint;
 use rustc_resolve as resolve;
 use rustc_session::lint;
 
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index c6706413942..6a23b230e12 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -73,8 +73,6 @@ use crate::html::markdown::{self, ErrorCodes, IdMap, Markdown, MarkdownHtml, Mar
 use crate::html::sources;
 use crate::html::{highlight, layout, static_files};
 
-use minifier;
-
 #[cfg(test)]
 mod tests;
 
@@ -3629,14 +3627,7 @@ fn render_impl(
                 for it in &i.inner_impl().items {
                     if let clean::TypedefItem(ref tydef, _) = it.inner {
                         write!(w, "<span class=\"where fmt-newline\">  ");
-                        assoc_type(
-                            w,
-                            it,
-                            &vec![],
-                            Some(&tydef.type_),
-                            AssocItemLink::Anchor(None),
-                            "",
-                        );
+                        assoc_type(w, it, &[], Some(&tydef.type_), AssocItemLink::Anchor(None), "");
                         write!(w, ";</span>");
                     }
                 }
diff --git a/src/librustdoc/markdown.rs b/src/librustdoc/markdown.rs
index 912a40722b8..a37efc22c93 100644
--- a/src/librustdoc/markdown.rs
+++ b/src/librustdoc/markdown.rs
@@ -5,7 +5,6 @@ use std::path::PathBuf;
 use rustc_feature::UnstableFeatures;
 use rustc_span::edition::Edition;
 use rustc_span::source_map::DUMMY_SP;
-use testing;
 
 use crate::config::{Options, RenderOptions};
 use crate::externalfiles::{load_string, LoadStringError};
diff --git a/src/librustdoc/passes/collect_intra_doc_links.rs b/src/librustdoc/passes/collect_intra_doc_links.rs
index 50d5f70f488..332d19fbfae 100644
--- a/src/librustdoc/passes/collect_intra_doc_links.rs
+++ b/src/librustdoc/passes/collect_intra_doc_links.rs
@@ -13,7 +13,6 @@ use rustc_hir::def_id::DefId;
 use rustc_resolve::ParentScope;
 use rustc_span::symbol::Symbol;
 use rustc_span::DUMMY_SP;
-use syntax;
 use syntax::ast::{self, Ident};
 
 use std::ops::Range;
diff --git a/src/librustdoc/test.rs b/src/librustdoc/test.rs
index 936f63975a5..2892c4b1537 100644
--- a/src/librustdoc/test.rs
+++ b/src/librustdoc/test.rs
@@ -20,7 +20,6 @@ use std::str;
 use syntax::ast;
 use syntax::with_globals;
 use tempfile::Builder as TempFileBuilder;
-use testing;
 
 use crate::clean::Attributes;
 use crate::config::Options;
diff --git a/src/libtest/cli.rs b/src/libtest/cli.rs
index edff8bea0f3..778600b2196 100644
--- a/src/libtest/cli.rs
+++ b/src/libtest/cli.rs
@@ -1,6 +1,5 @@
 //! Module converting command-line arguments into test configuration.
 
-use getopts;
 use std::env;
 use std::path::PathBuf;
 
diff --git a/src/libtest/console.rs b/src/libtest/console.rs
index ebdfb162947..149c9202e6e 100644
--- a/src/libtest/console.rs
+++ b/src/libtest/console.rs
@@ -4,8 +4,6 @@ use std::fs::File;
 use std::io;
 use std::io::prelude::Write;
 
-use term;
-
 use super::{
     bench::fmt_bench_samples,
     cli::TestOpts,
diff --git a/src/test/ui/proc-macro/auxiliary/issue-59191.rs b/src/test/ui/proc-macro/auxiliary/issue-59191.rs
new file mode 100644
index 00000000000..d9ee77067ec
--- /dev/null
+++ b/src/test/ui/proc-macro/auxiliary/issue-59191.rs
@@ -0,0 +1,16 @@
+// edition:2018
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro_attribute]
+pub fn no_main(_attrs: TokenStream, _input: TokenStream) -> TokenStream {
+    let new_krate = r#"
+        fn main() {}
+    "#;
+    new_krate.parse().unwrap()
+}
diff --git a/src/test/ui/proc-macro/issue-59191-replace-root-with-fn.rs b/src/test/ui/proc-macro/issue-59191-replace-root-with-fn.rs
new file mode 100644
index 00000000000..a59cacb8bde
--- /dev/null
+++ b/src/test/ui/proc-macro/issue-59191-replace-root-with-fn.rs
@@ -0,0 +1,8 @@
+// edition:2018
+// aux-crate:issue_59191=issue-59191.rs
+// Test that using a macro to replace the entire crate tree with a non-'mod' item errors out nicely.
+// `issue_59191::no_main` replaces whatever's passed in with `fn main() {}`.
+#![feature(custom_inner_attributes)]
+//~^ ERROR `main` function not found in crate `issue_59191_replace_root_with_fn` [E0601]
+#![issue_59191::no_main]
+//~^ ERROR expected crate top-level item to be a module after macro expansion, found a function
diff --git a/src/test/ui/proc-macro/issue-59191-replace-root-with-fn.stderr b/src/test/ui/proc-macro/issue-59191-replace-root-with-fn.stderr
new file mode 100644
index 00000000000..e0a3caef9db
--- /dev/null
+++ b/src/test/ui/proc-macro/issue-59191-replace-root-with-fn.stderr
@@ -0,0 +1,17 @@
+error: expected crate top-level item to be a module after macro expansion, found a function
+  --> $DIR/issue-59191-replace-root-with-fn.rs:7:1
+   |
+LL | #![issue_59191::no_main]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0601]: `main` function not found in crate `issue_59191_replace_root_with_fn`
+  --> $DIR/issue-59191-replace-root-with-fn.rs:5:1
+   |
+LL | / #![feature(custom_inner_attributes)]
+LL | |
+LL | | #![issue_59191::no_main]
+   | |________________________^ consider adding a `main` function to `$DIR/issue-59191-replace-root-with-fn.rs`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/suggestions/suggest-split-at-mut.rs b/src/test/ui/suggestions/suggest-split-at-mut.rs
new file mode 100644
index 00000000000..d294c20b824
--- /dev/null
+++ b/src/test/ui/suggestions/suggest-split-at-mut.rs
@@ -0,0 +1,8 @@
+fn main() {
+    let mut foo = [1, 2, 3, 4];
+    let a = &mut foo[2];
+    let b = &mut foo[3]; //~ ERROR cannot borrow `foo[_]` as mutable more than once at a time
+    *a = 5;
+    *b = 6;
+    println!("{:?} {:?}", a, b);
+}
diff --git a/src/test/ui/suggestions/suggest-split-at-mut.stderr b/src/test/ui/suggestions/suggest-split-at-mut.stderr
new file mode 100644
index 00000000000..330f012b2a9
--- /dev/null
+++ b/src/test/ui/suggestions/suggest-split-at-mut.stderr
@@ -0,0 +1,15 @@
+error[E0499]: cannot borrow `foo[_]` as mutable more than once at a time
+  --> $DIR/suggest-split-at-mut.rs:4:13
+   |
+LL |     let a = &mut foo[2];
+   |             ----------- first mutable borrow occurs here
+LL |     let b = &mut foo[3];
+   |             ^^^^^^^^^^^ second mutable borrow occurs here
+LL |     *a = 5;
+   |     ------ first borrow later used here
+   |
+   = help: consider using `.split_at_mut(position)` or similar method to obtain two mutable non-overlapping sub-slices
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0499`.