Auto merge of #97224 - matthiaskrgr:rollup-it5nw68, r=matthiaskrgr

Rollup of 7 pull requests

Successful merges:

 - #97109 (Fix misleading `cannot infer type for type parameter` error)
 - #97187 (Reverse condition in Vec::retain_mut doctest)
 - #97201 (Fix typo)
 - #97203 (Minor tweaks to rustc book summary formatting.)
 - #97208 (Do not emit the lint `unused_attributes` for *inherent* `#[doc(hidden)]` associated items)
 - #97215 (Add complexity estimation of iterating over HashSet and HashMap)
 - #97220 (Add regression test for#81827)

Failed merges:

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

41 files changed, 312 insertions, 40 deletions

diff --git a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
index 62edfc6495c..e1a2a237c23 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
@@ -866,6 +866,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 }
             }
 
+            self.report_ambiguous_type_parameter(&mut err, arg);
             err.span_label(
                 span,
                 arg_data.cannot_infer_msg(use_diag.filter(|d| d.applies_to(span))),
@@ -933,6 +934,28 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
     }
 
+    fn report_ambiguous_type_parameter(&self, err: &mut Diagnostic, arg: GenericArg<'tcx>) {
+        if let GenericArgKind::Type(ty) = arg.unpack()
+            && let ty::Infer(ty::TyVar(ty_vid)) = *ty.kind()
+        {
+            let mut inner = self.inner.borrow_mut();
+            let ty_vars = &inner.type_variables();
+            let var_origin = ty_vars.var_origin(ty_vid);
+            if let TypeVariableOriginKind::TypeParameterDefinition(_, Some(def_id)) =
+                var_origin.kind
+                && let Some(parent_def_id) = self.tcx.parent(def_id).as_local()
+                && let Some(node) = self.tcx.hir().find_by_def_id(parent_def_id)
+            {
+                match node {
+                    hir::Node::Item(item) if matches!(item.kind, hir::ItemKind::Impl(_) | hir::ItemKind::Fn(..)) => (),
+                    hir::Node::ImplItem(impl_item) if matches!(impl_item.kind, hir::ImplItemKind::Fn(..)) => (),
+                    _ => return,
+                }
+                err.span_help(self.tcx.def_span(def_id), "type parameter declared here");
+            }
+        }
+    }
+
     pub fn need_type_info_err_in_generator(
         &self,
         kind: hir::GeneratorKind,
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index ab3319a1186..3d5da114ecf 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -832,7 +832,7 @@ impl CheckAttrVisitor<'_> {
             let parent_hir_id = self.tcx.hir().get_parent_item(hir_id);
             let containing_item = self.tcx.hir().expect_item(parent_hir_id);
 
-            if Target::from_item(containing_item) == Target::Impl {
+            if let hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = containing_item.kind {
                 let meta_items = attr.meta_item_list().unwrap();
 
                 let (span, replacement_span) = if meta_items.len() == 1 {
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 3dc8a4fbba8..62bc04cadee 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -1470,11 +1470,11 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// ```
     /// let mut vec = vec![1, 2, 3, 4];
-    /// vec.retain_mut(|x| if *x > 3 {
-    ///     false
-    /// } else {
+    /// vec.retain_mut(|x| if *x <= 3 {
     ///     *x += 1;
     ///     true
+    /// } else {
+    ///     false
     /// });
     /// assert_eq!(vec, [2, 3, 4]);
     /// ```
diff --git a/library/std/src/collections/hash/map.rs b/library/std/src/collections/hash/map.rs
index 977714281fb..969f5dde4f0 100644
--- a/library/std/src/collections/hash/map.rs
+++ b/library/std/src/collections/hash/map.rs
@@ -344,6 +344,11 @@ impl<K, V, S> HashMap<K, V, S> {
     ///     println!("{key}");
     /// }
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, iterating over keys takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn keys(&self) -> Keys<'_, K, V> {
         Keys { inner: self.iter() }
@@ -370,6 +375,11 @@ impl<K, V, S> HashMap<K, V, S> {
     /// vec.sort_unstable();
     /// assert_eq!(vec, ["a", "b", "c"]);
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, iterating over keys takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[inline]
     #[rustc_lint_query_instability]
     #[stable(feature = "map_into_keys_values", since = "1.54.0")]
@@ -395,6 +405,11 @@ impl<K, V, S> HashMap<K, V, S> {
     ///     println!("{val}");
     /// }
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, iterating over values takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn values(&self) -> Values<'_, K, V> {
         Values { inner: self.iter() }
@@ -422,6 +437,11 @@ impl<K, V, S> HashMap<K, V, S> {
     ///     println!("{val}");
     /// }
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, iterating over values takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[stable(feature = "map_values_mut", since = "1.10.0")]
     pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
         ValuesMut { inner: self.iter_mut() }
@@ -448,6 +468,11 @@ impl<K, V, S> HashMap<K, V, S> {
     /// vec.sort_unstable();
     /// assert_eq!(vec, [1, 2, 3]);
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, iterating over values takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[inline]
     #[rustc_lint_query_instability]
     #[stable(feature = "map_into_keys_values", since = "1.54.0")]
@@ -473,6 +498,11 @@ impl<K, V, S> HashMap<K, V, S> {
     ///     println!("key: {key} val: {val}");
     /// }
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, iterating over map takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[rustc_lint_query_instability]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn iter(&self) -> Iter<'_, K, V> {
@@ -503,6 +533,11 @@ impl<K, V, S> HashMap<K, V, S> {
     ///     println!("key: {key} val: {val}");
     /// }
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, iterating over map takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[rustc_lint_query_instability]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
@@ -633,6 +668,11 @@ impl<K, V, S> HashMap<K, V, S> {
     /// map.retain(|&k, _| k % 2 == 0);
     /// assert_eq!(map.len(), 4);
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, this operation takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[inline]
     #[rustc_lint_query_instability]
     #[stable(feature = "retain_hash_collection", since = "1.18.0")]
diff --git a/library/std/src/collections/hash/set.rs b/library/std/src/collections/hash/set.rs
index 13bba0a6fd8..4ac0e081c2e 100644
--- a/library/std/src/collections/hash/set.rs
+++ b/library/std/src/collections/hash/set.rs
@@ -184,6 +184,11 @@ impl<T, S> HashSet<T, S> {
     ///     println!("{x}");
     /// }
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, iterating over set takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[inline]
     #[rustc_lint_query_instability]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -312,6 +317,11 @@ impl<T, S> HashSet<T, S> {
     /// set.retain(|&k| k % 2 == 0);
     /// assert_eq!(set.len(), 3);
     /// ```
+    ///
+    /// # Performance
+    ///
+    /// In the current implementation, this operation takes O(capacity) time
+    /// instead of O(len) because it internally visits empty buckets too.
     #[rustc_lint_query_instability]
     #[stable(feature = "retain_hash_collection", since = "1.18.0")]
     pub fn retain<F>(&mut self, f: F)
diff --git a/src/doc/rustc/src/SUMMARY.md b/src/doc/rustc/src/SUMMARY.md
index c2d44ac0e4d..7b2c35c0593 100644
--- a/src/doc/rustc/src/SUMMARY.md
+++ b/src/doc/rustc/src/SUMMARY.md
@@ -1,19 +1,20 @@
 # The Rustc Book
 
 - [What is rustc?](what-is-rustc.md)
-- [Command-line arguments](command-line-arguments.md)
+- [Command-line Arguments](command-line-arguments.md)
+    - [Codegen Options](codegen-options/index.md)
 - [Lints](lints/index.md)
-    - [Lint levels](lints/levels.md)
+    - [Lint Levels](lints/levels.md)
     - [Lint Groups](lints/groups.md)
-    - [Lint listing](lints/listing/index.md)
-        - [Allowed-by-default lints](lints/listing/allowed-by-default.md)
-        - [Warn-by-default lints](lints/listing/warn-by-default.md)
-        - [Deny-by-default lints](lints/listing/deny-by-default.md)
-- [Codegen options](codegen-options/index.md)
+    - [Lint Listing](lints/listing/index.md)
+        - [Allowed-by-default Lints](lints/listing/allowed-by-default.md)
+        - [Warn-by-default Lints](lints/listing/warn-by-default.md)
+        - [Deny-by-default Lints](lints/listing/deny-by-default.md)
 - [JSON Output](json.md)
 - [Tests](tests/index.md)
 - [Platform Support](platform-support.md)
-    - [Template for target-specific documentation](platform-support/TEMPLATE.md)
+    - [Target Tier Policy](target-tier-policy.md)
+    - [Template for Target-specific Documentation](platform-support/TEMPLATE.md)
     - [aarch64-apple-ios-sim](platform-support/aarch64-apple-ios-sim.md)
     - [armv7-unknown-linux-uclibceabi](platform-support/armv7-unknown-linux-uclibceabi.md)
     - [armv7-unknown-linux-uclibceabihf](platform-support/armv7-unknown-linux-uclibceabihf.md)
@@ -25,13 +26,12 @@
     - [*-unknown-openbsd](platform-support/openbsd.md)
     - [wasm64-unknown-unknown](platform-support/wasm64-unknown-unknown.md)
     - [x86_64-unknown-none](platform-support/x86_64-unknown-none.md)
-- [Target Tier Policy](target-tier-policy.md)
 - [Targets](targets/index.md)
     - [Built-in Targets](targets/built-in.md)
     - [Custom Targets](targets/custom.md)
     - [Known Issues](targets/known-issues.md)
 - [Profile-guided Optimization](profile-guided-optimization.md)
 - [Instrumentation-based Code Coverage](instrument-coverage.md)
-- [Linker-plugin based LTO](linker-plugin-lto.md)
+- [Linker-plugin-based LTO](linker-plugin-lto.md)
 - [Exploit Mitigations](exploit-mitigations.md)
 - [Contributing to `rustc`](contributing.md)
diff --git a/src/doc/rustc/src/codegen-options/index.md b/src/doc/rustc/src/codegen-options/index.md
index 02011325d68..b1c3b618cec 100644
--- a/src/doc/rustc/src/codegen-options/index.md
+++ b/src/doc/rustc/src/codegen-options/index.md
@@ -1,4 +1,4 @@
-# Codegen options
+# Codegen Options
 
 All of these options are passed to `rustc` via the `-C` flag, short for "codegen." You can see
 a version of this list for your exact compiler by running `rustc -C help`.
diff --git a/src/doc/rustc/src/command-line-arguments.md b/src/doc/rustc/src/command-line-arguments.md
index d80e4f20869..73e7764a11d 100644
--- a/src/doc/rustc/src/command-line-arguments.md
+++ b/src/doc/rustc/src/command-line-arguments.md
@@ -1,4 +1,4 @@
-# Command-line arguments
+# Command-line Arguments
 
 Here's a list of command-line arguments to `rustc` and what they do.
 
diff --git a/src/doc/rustc/src/instrument-coverage.md b/src/doc/rustc/src/instrument-coverage.md
index 108b0ffe99b..0ae9e53af3c 100644
--- a/src/doc/rustc/src/instrument-coverage.md
+++ b/src/doc/rustc/src/instrument-coverage.md
@@ -1,4 +1,4 @@
-# `instrument-coverage`
+# Instrumentation-based Code Coverage
 
 ## Introduction
 
diff --git a/src/doc/rustc/src/linker-plugin-lto.md b/src/doc/rustc/src/linker-plugin-lto.md
index e7bf8d9a36f..9c644dd404d 100644
--- a/src/doc/rustc/src/linker-plugin-lto.md
+++ b/src/doc/rustc/src/linker-plugin-lto.md
@@ -1,4 +1,4 @@
-# Linker-plugin-LTO
+# Linker-plugin-based LTO
 
 The `-C linker-plugin-lto` flag allows for deferring the LTO optimization
 to the actual linking step, which in turn allows for performing
diff --git a/src/doc/rustc/src/lints/levels.md b/src/doc/rustc/src/lints/levels.md
index fbec3cd9baf..93892d6ade6 100644
--- a/src/doc/rustc/src/lints/levels.md
+++ b/src/doc/rustc/src/lints/levels.md
@@ -1,4 +1,4 @@
-# Lint levels
+# Lint Levels
 
 In `rustc`, lints are divided into five *levels*:
 
diff --git a/src/doc/rustc/src/lints/listing/allowed-by-default.md b/src/doc/rustc/src/lints/listing/allowed-by-default.md
index 95dd60bebfb..8c4c0b9c558 100644
--- a/src/doc/rustc/src/lints/listing/allowed-by-default.md
+++ b/src/doc/rustc/src/lints/listing/allowed-by-default.md
@@ -1,3 +1,3 @@
-# Allowed-by-default lints
+# Allowed-by-default Lints
 
 This file is auto-generated by the lint-docs script.
diff --git a/src/doc/rustc/src/lints/listing/deny-by-default.md b/src/doc/rustc/src/lints/listing/deny-by-default.md
index 3c1452d6467..12f511423b4 100644
--- a/src/doc/rustc/src/lints/listing/deny-by-default.md
+++ b/src/doc/rustc/src/lints/listing/deny-by-default.md
@@ -1,3 +1,3 @@
-# Deny-by-default lints
+# Deny-by-default Lints
 
 This file is auto-generated by the lint-docs script.
diff --git a/src/doc/rustc/src/lints/listing/index.md b/src/doc/rustc/src/lints/listing/index.md
index 97aa2caf915..791a80274e2 100644
--- a/src/doc/rustc/src/lints/listing/index.md
+++ b/src/doc/rustc/src/lints/listing/index.md
@@ -1,4 +1,4 @@
-# Lint listing
+# Lint Listing
 
 This section lists out all of the lints, grouped by their default lint levels.
 
diff --git a/src/doc/rustc/src/lints/listing/warn-by-default.md b/src/doc/rustc/src/lints/listing/warn-by-default.md
index eebc022a82b..84d67764f7d 100644
--- a/src/doc/rustc/src/lints/listing/warn-by-default.md
+++ b/src/doc/rustc/src/lints/listing/warn-by-default.md
@@ -1,3 +1,3 @@
-# Warn-by-default lints
+# Warn-by-default Lints
 
 This file is auto-generated by the lint-docs script.
diff --git a/src/doc/rustc/src/platform-support/pc-windows-gnullvm.md b/src/doc/rustc/src/platform-support/pc-windows-gnullvm.md
index 96ae065b31b..721c234c6e6 100644
--- a/src/doc/rustc/src/platform-support/pc-windows-gnullvm.md
+++ b/src/doc/rustc/src/platform-support/pc-windows-gnullvm.md
@@ -4,7 +4,7 @@
 
 Windows targets similar to `*-pc-windows-gnu` but using UCRT as the runtime and various LLVM tools/libraries instead of GCC/Binutils.
 
-Target triples avaiable so far:
+Target triples available so far:
 - `aarch64-pc-windows-gnullvm`
 - `x86_64-pc-windows-gnullvm`
 
@@ -26,7 +26,7 @@ Like with any other Windows target created binaries are in PE format.
 ## Building the target
 
 For cross-compilation I recommend using [llvm-mingw](https://github.com/mstorsjo/llvm-mingw) toolchain, one change that seems necessary beside configuring corss compilers is disabling experimental `m86k` target. Otherwise LLVM build fails with `multiple definition ...` errors.
-Native bootstrapping builds require rather fragile hacks until host artifacts are avaiable so I won't describe them here.
+Native bootstrapping builds require rather fragile hacks until host artifacts are available so I won't describe them here.
 
 ## Building Rust programs
 
diff --git a/src/doc/rustc/src/profile-guided-optimization.md b/src/doc/rustc/src/profile-guided-optimization.md
index d066f4a9cf5..d9cf7ce30f9 100644
--- a/src/doc/rustc/src/profile-guided-optimization.md
+++ b/src/doc/rustc/src/profile-guided-optimization.md
@@ -1,4 +1,4 @@
-# Profile Guided Optimization
+# Profile-guided Optimization
 
 `rustc` supports doing profile-guided optimization (PGO).
 This chapter describes what PGO is, what it is good for, and how it can be used.
diff --git a/src/test/ui/const-generics/issues/issue-83249.stderr b/src/test/ui/const-generics/issues/issue-83249.stderr
index 402b3aa2d61..3f44a54e80a 100644
--- a/src/test/ui/const-generics/issues/issue-83249.stderr
+++ b/src/test/ui/const-generics/issues/issue-83249.stderr
@@ -5,6 +5,12 @@ LL |     let _ = foo([0; 1]);
    |         -   ^^^ cannot infer type for type parameter `T` declared on the function `foo`
    |         |
    |         consider giving this pattern a type
+   |
+help: type parameter declared here
+  --> $DIR/issue-83249.rs:12:8
+   |
+LL | fn foo<T: Foo>(_: [u8; T::N]) -> T {
+   |        ^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/consts/issue-64662.stderr b/src/test/ui/consts/issue-64662.stderr
index dd281e911da..caa582d87f5 100644
--- a/src/test/ui/consts/issue-64662.stderr
+++ b/src/test/ui/consts/issue-64662.stderr
@@ -3,12 +3,24 @@ error[E0282]: type annotations needed
    |
 LL |     A = foo(),
    |         ^^^ cannot infer type for type parameter `T` declared on the function `foo`
+   |
+help: type parameter declared here
+  --> $DIR/issue-64662.rs:6:14
+   |
+LL | const fn foo<T>() -> isize {
+   |              ^
 
 error[E0282]: type annotations needed
   --> $DIR/issue-64662.rs:3:9
    |
 LL |     B = foo(),
    |         ^^^ cannot infer type for type parameter `T` declared on the function `foo`
+   |
+help: type parameter declared here
+  --> $DIR/issue-64662.rs:6:14
+   |
+LL | const fn foo<T>() -> isize {
+   |              ^
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/error-codes/E0401.stderr b/src/test/ui/error-codes/E0401.stderr
index 8b1d4e6c07c..e58c9d3116a 100644
--- a/src/test/ui/error-codes/E0401.stderr
+++ b/src/test/ui/error-codes/E0401.stderr
@@ -37,6 +37,12 @@ error[E0282]: type annotations needed
    |
 LL |     bfnr(x);
    |     ^^^^ cannot infer type for type parameter `U` declared on the function `bfnr`
+   |
+help: type parameter declared here
+  --> $DIR/E0401.rs:4:13
+   |
+LL |     fn bfnr<U, V: Baz<U>, W: Fn()>(y: T) {
+   |             ^
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/inference/ambiguous_type_parameter.rs b/src/test/ui/inference/ambiguous_type_parameter.rs
new file mode 100644
index 00000000000..dc70ed661d2
--- /dev/null
+++ b/src/test/ui/inference/ambiguous_type_parameter.rs
@@ -0,0 +1,17 @@
+use std::collections::HashMap;
+
+trait Store<K, V> {
+    fn get_raw(&self, key: &K) -> Option<()>;
+}
+
+struct InMemoryStore;
+
+impl<K> Store<String, HashMap<K, String>> for InMemoryStore {
+    fn get_raw(&self, key: &String) -> Option<()> {
+        None
+    }
+}
+
+fn main() {
+    InMemoryStore.get_raw(&String::default()); //~ ERROR type annotations needed
+}
diff --git a/src/test/ui/inference/ambiguous_type_parameter.stderr b/src/test/ui/inference/ambiguous_type_parameter.stderr
new file mode 100644
index 00000000000..47ef1948aee
--- /dev/null
+++ b/src/test/ui/inference/ambiguous_type_parameter.stderr
@@ -0,0 +1,15 @@
+error[E0282]: type annotations needed
+  --> $DIR/ambiguous_type_parameter.rs:16:19
+   |
+LL |     InMemoryStore.get_raw(&String::default());
+   |                   ^^^^^^^ cannot infer type for type parameter `K`
+   |
+help: type parameter declared here
+  --> $DIR/ambiguous_type_parameter.rs:9:6
+   |
+LL | impl<K> Store<String, HashMap<K, String>> for InMemoryStore {
+   |      ^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.
diff --git a/src/test/ui/inference/erase-type-params-in-label.stderr b/src/test/ui/inference/erase-type-params-in-label.stderr
index d0b06cde9d6..51fac5f79df 100644
--- a/src/test/ui/inference/erase-type-params-in-label.stderr
+++ b/src/test/ui/inference/erase-type-params-in-label.stderr
@@ -6,6 +6,11 @@ LL |     let foo = foo(1, "");
    |         |
    |         consider giving `foo` the explicit type `Foo<_, _, W, Z>`, where the type parameter `W` is specified
    |
+help: type parameter declared here
+  --> $DIR/erase-type-params-in-label.rs:25:14
+   |
+LL | fn foo<T, K, W: Default, Z: Default>(t: T, k: K) -> Foo<T, K, W, Z> {
+   |              ^
    = note: cannot satisfy `_: Default`
 note: required by a bound in `foo`
   --> $DIR/erase-type-params-in-label.rs:25:17
@@ -25,6 +30,11 @@ LL |     let bar = bar(1, "");
    |         |
    |         consider giving `bar` the explicit type `Bar<_, _, Z>`, where the type parameter `Z` is specified
    |
+help: type parameter declared here
+  --> $DIR/erase-type-params-in-label.rs:14:14
+   |
+LL | fn bar<T, K, Z: Default>(t: T, k: K) -> Bar<T, K, Z> {
+   |              ^
    = note: cannot satisfy `_: Default`
 note: required by a bound in `bar`
   --> $DIR/erase-type-params-in-label.rs:14:17
diff --git a/src/test/ui/inference/issue-86162-1.stderr b/src/test/ui/inference/issue-86162-1.stderr
index 8d6f50748cb..edf97c0aed4 100644
--- a/src/test/ui/inference/issue-86162-1.stderr
+++ b/src/test/ui/inference/issue-86162-1.stderr
@@ -4,6 +4,11 @@ error[E0283]: type annotations needed
 LL |     foo(gen()); //<- Do not suggest `foo::<impl Clone>()`!
    |     ^^^ cannot infer type for type parameter `impl Clone` declared on the function `foo`
    |
+help: type parameter declared here
+  --> $DIR/issue-86162-1.rs:3:11
+   |
+LL | fn foo(x: impl Clone) {}
+   |           ^^^^^^^^^^
    = note: cannot satisfy `_: Clone`
 note: required by a bound in `foo`
   --> $DIR/issue-86162-1.rs:3:16
diff --git a/src/test/ui/inference/issue-86162-2.stderr b/src/test/ui/inference/issue-86162-2.stderr
index 5f80c595628..c642ebb0576 100644
--- a/src/test/ui/inference/issue-86162-2.stderr
+++ b/src/test/ui/inference/issue-86162-2.stderr
@@ -4,6 +4,11 @@ error[E0283]: type annotations needed
 LL |     Foo::bar(gen()); //<- Do not suggest `Foo::bar::<impl Clone>()`!
    |     ^^^^^^^^ cannot infer type for type parameter `impl Clone` declared on the associated function `bar`
    |
+help: type parameter declared here
+  --> $DIR/issue-86162-2.rs:8:15
+   |
+LL |     fn bar(x: impl Clone) {}
+   |               ^^^^^^^^^^
    = note: cannot satisfy `_: Clone`
 note: required by a bound in `Foo::bar`
   --> $DIR/issue-86162-2.rs:8:20
diff --git a/src/test/ui/issues/issue-6458.stderr b/src/test/ui/issues/issue-6458.stderr
index f1a982616a4..f548692d785 100644
--- a/src/test/ui/issues/issue-6458.stderr
+++ b/src/test/ui/issues/issue-6458.stderr
@@ -3,6 +3,12 @@ error[E0282]: type annotations needed
    |
 LL |    foo(TypeWithState(marker::PhantomData));
    |    ^^^ cannot infer type for type parameter `State` declared on the function `foo`
+   |
+help: type parameter declared here
+  --> $DIR/issue-6458.rs:6:12
+   |
+LL | pub fn foo<State>(_: TypeWithState<State>) {}
+   |            ^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/lint/unused/unused-attr-doc-hidden.fixed b/src/test/ui/lint/unused/unused-attr-doc-hidden.fixed
index 36a14097ac3..362ad55707a 100644
--- a/src/test/ui/lint/unused/unused-attr-doc-hidden.fixed
+++ b/src/test/ui/lint/unused/unused-attr-doc-hidden.fixed
@@ -1,5 +1,7 @@
-#![deny(unused_attributes)]
+#![feature(inherent_associated_types)]
+#![allow(dead_code, incomplete_features)]
 #![crate_type = "lib"]
+#![deny(unused_attributes)]
 // run-rustfix
 
 pub trait Trait {
@@ -12,6 +14,17 @@ pub trait Trait {
 
 pub struct Implementor;
 
+impl Implementor {
+    #[doc(hidden)] // no error
+    type Inh = ();
+
+    #[doc(hidden)] // no error
+    const INH: () = ();
+
+    #[doc(hidden)] // no error
+    fn inh() {}
+}
+
 impl Trait for Implementor {
     
     type It = ();
diff --git a/src/test/ui/lint/unused/unused-attr-doc-hidden.rs b/src/test/ui/lint/unused/unused-attr-doc-hidden.rs
index e58c4f22f31..d493ed6dae2 100644
--- a/src/test/ui/lint/unused/unused-attr-doc-hidden.rs
+++ b/src/test/ui/lint/unused/unused-attr-doc-hidden.rs
@@ -1,5 +1,7 @@
-#![deny(unused_attributes)]
+#![feature(inherent_associated_types)]
+#![allow(dead_code, incomplete_features)]
 #![crate_type = "lib"]
+#![deny(unused_attributes)]
 // run-rustfix
 
 pub trait Trait {
@@ -12,6 +14,17 @@ pub trait Trait {
 
 pub struct Implementor;
 
+impl Implementor {
+    #[doc(hidden)] // no error
+    type Inh = ();
+
+    #[doc(hidden)] // no error
+    const INH: () = ();
+
+    #[doc(hidden)] // no error
+    fn inh() {}
+}
+
 impl Trait for Implementor {
     #[doc(hidden)]
     type It = ();
diff --git a/src/test/ui/lint/unused/unused-attr-doc-hidden.stderr b/src/test/ui/lint/unused/unused-attr-doc-hidden.stderr
index fd1202a29de..f167bd460db 100644
--- a/src/test/ui/lint/unused/unused-attr-doc-hidden.stderr
+++ b/src/test/ui/lint/unused/unused-attr-doc-hidden.stderr
@@ -1,11 +1,11 @@
 error: `#[doc(hidden)]` is ignored on trait impl items
-  --> $DIR/unused-attr-doc-hidden.rs:16:5
+  --> $DIR/unused-attr-doc-hidden.rs:29:5
    |
 LL |     #[doc(hidden)]
    |     ^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: the lint level is defined here
-  --> $DIR/unused-attr-doc-hidden.rs:1:9
+  --> $DIR/unused-attr-doc-hidden.rs:4:9
    |
 LL | #![deny(unused_attributes)]
    |         ^^^^^^^^^^^^^^^^^
@@ -13,7 +13,7 @@ LL | #![deny(unused_attributes)]
    = note: whether the impl item is `doc(hidden)` or not entirely depends on the corresponding trait item
 
 error: `#[doc(hidden)]` is ignored on trait impl items
-  --> $DIR/unused-attr-doc-hidden.rs:21:5
+  --> $DIR/unused-attr-doc-hidden.rs:34:5
    |
 LL |     #[doc(hidden)]
    |     ^^^^^^^^^^^^^^ help: remove this attribute
@@ -22,7 +22,7 @@ LL |     #[doc(hidden)]
    = note: whether the impl item is `doc(hidden)` or not entirely depends on the corresponding trait item
 
 error: `#[doc(hidden)]` is ignored on trait impl items
-  --> $DIR/unused-attr-doc-hidden.rs:26:11
+  --> $DIR/unused-attr-doc-hidden.rs:39:11
    |
 LL |     #[doc(hidden, alias = "aka")]
    |           ^^^^^^--
@@ -33,7 +33,7 @@ LL |     #[doc(hidden, alias = "aka")]
    = note: whether the impl item is `doc(hidden)` or not entirely depends on the corresponding trait item
 
 error: `#[doc(hidden)]` is ignored on trait impl items
-  --> $DIR/unused-attr-doc-hidden.rs:31:27
+  --> $DIR/unused-attr-doc-hidden.rs:44:27
    |
 LL |     #[doc(alias = "this", hidden,)]
    |                           ^^^^^^-
@@ -44,7 +44,7 @@ LL |     #[doc(alias = "this", hidden,)]
    = note: whether the impl item is `doc(hidden)` or not entirely depends on the corresponding trait item
 
 error: `#[doc(hidden)]` is ignored on trait impl items
-  --> $DIR/unused-attr-doc-hidden.rs:36:11
+  --> $DIR/unused-attr-doc-hidden.rs:49:11
    |
 LL |     #[doc(hidden, hidden)]
    |           ^^^^^^--
@@ -55,7 +55,7 @@ LL |     #[doc(hidden, hidden)]
    = note: whether the impl item is `doc(hidden)` or not entirely depends on the corresponding trait item
 
 error: `#[doc(hidden)]` is ignored on trait impl items
-  --> $DIR/unused-attr-doc-hidden.rs:36:19
+  --> $DIR/unused-attr-doc-hidden.rs:49:19
    |
 LL |     #[doc(hidden, hidden)]
    |                   ^^^^^^ help: remove this attribute
diff --git a/src/test/ui/missing/missing-items/missing-type-parameter.stderr b/src/test/ui/missing/missing-items/missing-type-parameter.stderr
index 1219badc5b3..2aa2b0e6a3c 100644
--- a/src/test/ui/missing/missing-items/missing-type-parameter.stderr
+++ b/src/test/ui/missing/missing-items/missing-type-parameter.stderr
@@ -3,6 +3,12 @@ error[E0282]: type annotations needed
    |
 LL |     foo();
    |     ^^^ cannot infer type for type parameter `X` declared on the function `foo`
+   |
+help: type parameter declared here
+  --> $DIR/missing-type-parameter.rs:1:8
+   |
+LL | fn foo<X>() { }
+   |        ^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/parser/issue-81827.rs b/src/test/ui/parser/issue-81827.rs
new file mode 100644
index 00000000000..7ec58159413
--- /dev/null
+++ b/src/test/ui/parser/issue-81827.rs
@@ -0,0 +1,11 @@
+// error-pattern: this file contains an unclosed delimiter
+// error-pattern: mismatched closing delimiter: `]`
+// error-pattern: expected one of `)` or `,`, found `{`
+
+#![crate_name="0"]
+
+
+
+fn main() {}
+
+fn r()->i{0|{#[cfg(r(0{]0
diff --git a/src/test/ui/parser/issue-81827.stderr b/src/test/ui/parser/issue-81827.stderr
new file mode 100644
index 00000000000..069de339194
--- /dev/null
+++ b/src/test/ui/parser/issue-81827.stderr
@@ -0,0 +1,35 @@
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-81827.rs:11:27
+   |
+LL | fn r()->i{0|{#[cfg(r(0{]0
+   |          -  -             ^
+   |          |  |
+   |          |  unclosed delimiter
+   |          unclosed delimiter
+
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-81827.rs:11:27
+   |
+LL | fn r()->i{0|{#[cfg(r(0{]0
+   |          -  -             ^
+   |          |  |
+   |          |  unclosed delimiter
+   |          unclosed delimiter
+
+error: mismatched closing delimiter: `]`
+  --> $DIR/issue-81827.rs:11:23
+   |
+LL | fn r()->i{0|{#[cfg(r(0{]0
+   |               -       ^^ mismatched closing delimiter
+   |               |       |
+   |               |       unclosed delimiter
+   |               closing delimiter possibly meant for this
+
+error: expected one of `)` or `,`, found `{`
+  --> $DIR/issue-81827.rs:11:23
+   |
+LL | fn r()->i{0|{#[cfg(r(0{]0
+   |                       ^ expected one of `)` or `,`
+
+error: aborting due to 4 previous errors
+
diff --git a/src/test/ui/suggestions/fn-needing-specified-return-type-param.stderr b/src/test/ui/suggestions/fn-needing-specified-return-type-param.stderr
index b59a3818e70..a4cfee55633 100644
--- a/src/test/ui/suggestions/fn-needing-specified-return-type-param.stderr
+++ b/src/test/ui/suggestions/fn-needing-specified-return-type-param.stderr
@@ -5,6 +5,12 @@ LL |     let _ = f;
    |         -   ^ cannot infer type for type parameter `A` declared on the function `f`
    |         |
    |         consider giving this pattern the explicit type `fn() -> A`, where the type parameter `A` is specified
+   |
+help: type parameter declared here
+  --> $DIR/fn-needing-specified-return-type-param.rs:1:6
+   |
+LL | fn f<A>() -> A { unimplemented!() }
+   |      ^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/traits/multidispatch-convert-ambig-dest.stderr b/src/test/ui/traits/multidispatch-convert-ambig-dest.stderr
index 9fd81b56bf1..da746134710 100644
--- a/src/test/ui/traits/multidispatch-convert-ambig-dest.stderr
+++ b/src/test/ui/traits/multidispatch-convert-ambig-dest.stderr
@@ -3,6 +3,12 @@ error[E0282]: type annotations needed
    |
 LL |     test(22, std::default::Default::default());
    |     ^^^^ cannot infer type for type parameter `U` declared on the function `test`
+   |
+help: type parameter declared here
+  --> $DIR/multidispatch-convert-ambig-dest.rs:20:11
+   |
+LL | fn test<T,U>(_: T, _: U)
+   |           ^
 
 error[E0283]: type annotations needed
   --> $DIR/multidispatch-convert-ambig-dest.rs:26:5
@@ -10,6 +16,11 @@ error[E0283]: type annotations needed
 LL |     test(22, std::default::Default::default());
    |     ^^^^ cannot infer type for type parameter `U` declared on the function `test`
    |
+help: type parameter declared here
+  --> $DIR/multidispatch-convert-ambig-dest.rs:20:11
+   |
+LL | fn test<T,U>(_: T, _: U)
+   |           ^
 note: multiple `impl`s satisfying `i32: Convert<_>` found
   --> $DIR/multidispatch-convert-ambig-dest.rs:8:1
    |
diff --git a/src/test/ui/traits/not-suggest-non-existing-fully-qualified-path.stderr b/src/test/ui/traits/not-suggest-non-existing-fully-qualified-path.stderr
index 65f2d99417f..3c8d7450f96 100644
--- a/src/test/ui/traits/not-suggest-non-existing-fully-qualified-path.stderr
+++ b/src/test/ui/traits/not-suggest-non-existing-fully-qualified-path.stderr
@@ -16,6 +16,11 @@ LL |     a.method();
    |     | cannot infer type for type parameter `U`
    |     this method call resolves to `U`
    |
+help: type parameter declared here
+  --> $DIR/not-suggest-non-existing-fully-qualified-path.rs:12:9
+   |
+LL | impl<T, U> V<U> for A<T>
+   |         ^
 note: multiple `impl`s satisfying `B: I<_>` found
   --> $DIR/not-suggest-non-existing-fully-qualified-path.rs:5:1
    |
diff --git a/src/test/ui/type-inference/unbounded-type-param-in-fn-with-assoc-type.stderr b/src/test/ui/type-inference/unbounded-type-param-in-fn-with-assoc-type.stderr
index d60ca4a4932..501fa7c8c67 100644
--- a/src/test/ui/type-inference/unbounded-type-param-in-fn-with-assoc-type.stderr
+++ b/src/test/ui/type-inference/unbounded-type-param-in-fn-with-assoc-type.stderr
@@ -3,6 +3,12 @@ error[E0282]: type annotations needed
    |
 LL |     foo();
    |     ^^^ cannot infer type for type parameter `T` declared on the function `foo`
+   |
+help: type parameter declared here
+  --> $DIR/unbounded-type-param-in-fn-with-assoc-type.rs:3:8
+   |
+LL | fn foo<T, U = u64>() -> (T, U) {
+   |        ^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/type-inference/unbounded-type-param-in-fn.stderr b/src/test/ui/type-inference/unbounded-type-param-in-fn.stderr
index 45d879d8d56..d01c3a7d4e2 100644
--- a/src/test/ui/type-inference/unbounded-type-param-in-fn.stderr
+++ b/src/test/ui/type-inference/unbounded-type-param-in-fn.stderr
@@ -3,6 +3,12 @@ error[E0282]: type annotations needed
    |
 LL |     foo();
    |     ^^^ cannot infer type for type parameter `T` declared on the function `foo`
+   |
+help: type parameter declared here
+  --> $DIR/unbounded-type-param-in-fn.rs:1:8
+   |
+LL | fn foo<T>() -> T {
+   |        ^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/type/type-annotation-needed.stderr b/src/test/ui/type/type-annotation-needed.stderr
index f7dfb845238..64fdbfe7db4 100644
--- a/src/test/ui/type/type-annotation-needed.stderr
+++ b/src/test/ui/type/type-annotation-needed.stderr
@@ -4,6 +4,11 @@ error[E0283]: type annotations needed
 LL |     foo(42);
    |     ^^^ cannot infer type for type parameter `T` declared on the function `foo`
    |
+help: type parameter declared here
+  --> $DIR/type-annotation-needed.rs:1:8
+   |
+LL | fn foo<T: Into<String>>(x: i32) {}
+   |        ^
    = note: cannot satisfy `_: Into<String>`
 note: required by a bound in `foo`
   --> $DIR/type-annotation-needed.rs:1:11
diff --git a/src/tools/lint-docs/src/lib.rs b/src/tools/lint-docs/src/lib.rs
index fdc89a184da..857feb77325 100644
--- a/src/tools/lint-docs/src/lib.rs
+++ b/src/tools/lint-docs/src/lib.rs
@@ -482,20 +482,20 @@ fn lint_name(line: &str) -> Result<String, &'static str> {
     }
 }
 
-static ALLOWED_MD: &str = r#"# Allowed-by-default lints
+static ALLOWED_MD: &str = r#"# Allowed-by-default Lints
 
 These lints are all set to the 'allow' level by default. As such, they won't show up
 unless you set them to a higher lint level with a flag or attribute.
 
 "#;
 
-static WARN_MD: &str = r#"# Warn-by-default lints
+static WARN_MD: &str = r#"# Warn-by-default Lints
 
 These lints are all set to the 'warn' level by default.
 
 "#;
 
-static DENY_MD: &str = r#"# Deny-by-default lints
+static DENY_MD: &str = r#"# Deny-by-default Lints
 
 These lints are all set to the 'deny' level by default.
 
diff --git a/src/tools/rustfmt/tests/source/cfg_if/detect/arch/x86.rs b/src/tools/rustfmt/tests/source/cfg_if/detect/arch/x86.rs
index 4c71a2c6ab9..d26f4ee894f 100644
--- a/src/tools/rustfmt/tests/source/cfg_if/detect/arch/x86.rs
+++ b/src/tools/rustfmt/tests/source/cfg_if/detect/arch/x86.rs
@@ -3,7 +3,7 @@
 //! The features are detected using the `detect_features` function below.
 //! This function uses the CPUID instruction to read the feature flags from the
 //! CPU and encodes them in a `usize` where each bit position represents
-//! whether a feature is available (bit is set) or unavaiable (bit is cleared).
+//! whether a feature is available (bit is set) or unavailable (bit is cleared).
 //!
 //! The enum `Feature` is used to map bit positions to feature names, and the
 //! the `__crate::detect::check_for!` macro is used to map string literals (e.g.,
diff --git a/src/tools/rustfmt/tests/target/cfg_if/detect/arch/x86.rs b/src/tools/rustfmt/tests/target/cfg_if/detect/arch/x86.rs
index b985dd8caa1..02d5eed1c29 100644
--- a/src/tools/rustfmt/tests/target/cfg_if/detect/arch/x86.rs
+++ b/src/tools/rustfmt/tests/target/cfg_if/detect/arch/x86.rs
@@ -3,7 +3,7 @@
 //! The features are detected using the `detect_features` function below.
 //! This function uses the CPUID instruction to read the feature flags from the
 //! CPU and encodes them in a `usize` where each bit position represents
-//! whether a feature is available (bit is set) or unavaiable (bit is cleared).
+//! whether a feature is available (bit is set) or unavailable (bit is cleared).
 //!
 //! The enum `Feature` is used to map bit positions to feature names, and the
 //! the `__crate::detect::check_for!` macro is used to map string literals (e.g.,