Auto merge of #94571 - matthiaskrgr:rollup-4ul5ydb, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #92697 (Use cgroup quotas for calculating `available_parallelism`)
 - #94057 (improve comments for `simplify_type`)
 - #94547 (`parse_tt` cleanups)
 - #94550 (rustdoc: Add test for higher kinded functions generated by macros)
 - #94551 (Doc: Fix use of quote instead of backstick in Adapter::map.)
 - #94554 (Fix invalid lint_node_id being put on a removed stmt)
 - #94555 (all: fix some typos)
 - #94563 (Remove a unnecessary `..` pattern)

Failed merges:

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

28 files changed, 328 insertions, 185 deletions

diff --git a/RELEASES.md b/RELEASES.md
index 971a63b240f..08040f48158 100644
--- a/RELEASES.md
+++ b/RELEASES.md
@@ -1060,7 +1060,7 @@ Version 1.52.1 (2021-05-10)
 This release disables incremental compilation, unless the user has explicitly
 opted in via the newly added RUSTC_FORCE_INCREMENTAL=1 environment variable.
 
-This is due to the widespread, and frequently occuring, breakage encountered by
+This is due to the widespread, and frequently occurring, breakage encountered by
 Rust users due to newly enabled incremental verification in 1.52.0. Notably,
 Rust users **should** upgrade to 1.52.0 or 1.52.1: the bugs that are detected by
 newly added incremental verification are still present in past stable versions,
diff --git a/compiler/rustc_codegen_gcc/src/builder.rs b/compiler/rustc_codegen_gcc/src/builder.rs
index 974e59b65ec..be3f6a12706 100644
--- a/compiler/rustc_codegen_gcc/src/builder.rs
+++ b/compiler/rustc_codegen_gcc/src/builder.rs
@@ -1064,7 +1064,7 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         let val_type = value.get_type();
         match (type_is_pointer(val_type), type_is_pointer(dest_ty)) {
             (false, true) => {
-                // NOTE: Projecting a field of a pointer type will attemp a cast from a signed char to
+                // NOTE: Projecting a field of a pointer type will attempt a cast from a signed char to
                 // a pointer, which is not supported by gccjit.
                 return self.cx.context.new_cast(None, self.inttoptr(value, val_type.make_pointer()), dest_ty);
             },
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index 3b06587061d..e9d13a4ebaf 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -369,12 +369,12 @@ pub fn target_cpu(sess: &Session) -> &str {
 /// The list of LLVM features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
 /// `--target` and similar).
 pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<String> {
-    // Features that come earlier are overriden by conflicting features later in the string.
+    // Features that come earlier are overridden by conflicting features later in the string.
     // Typically we'll want more explicit settings to override the implicit ones, so:
     //
-    // * Features from -Ctarget-cpu=*; are overriden by [^1]
-    // * Features implied by --target; are overriden by
-    // * Features from -Ctarget-feature; are overriden by
+    // * Features from -Ctarget-cpu=*; are overridden by [^1]
+    // * Features implied by --target; are overridden by
+    // * Features from -Ctarget-feature; are overridden by
     // * function specific features.
     //
     // [^1]: target-cpu=native is handled here, other target-cpu values are handled implicitly
@@ -383,7 +383,7 @@ pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<Str
     // FIXME(nagisa): it isn't clear what's the best interaction between features implied by
     // `-Ctarget-cpu` and `--target` are. On one hand, you'd expect CLI arguments to always
     // override anything that's implicit, so e.g. when there's no `--target` flag, features implied
-    // the host target are overriden by `-Ctarget-cpu=*`. On the other hand, what about when both
+    // the host target are overridden by `-Ctarget-cpu=*`. On the other hand, what about when both
     // `--target` and `-Ctarget-cpu=*` are specified? Both then imply some target features and both
     // flags are specified by the user on the CLI. It isn't as clear-cut which order of precedence
     // should be taken in cases like these.
diff --git a/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs b/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs
index 1561277b704..37e84046901 100644
--- a/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs
+++ b/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs
@@ -1,6 +1,6 @@
 // Type Names for Debug Info.
 
-// Notes on targetting MSVC:
+// Notes on targeting MSVC:
 // In general, MSVC's debugger attempts to parse all arguments as C++ expressions,
 // even if the argument is explicitly a symbol name.
 // As such, there are many things that cause parsing issues:
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
index 716c01ba78c..16870489176 100644
--- a/compiler/rustc_const_eval/src/interpret/operand.rs
+++ b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -535,7 +535,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let val =
                     self.subst_from_current_frame_and_normalize_erasing_regions(constant.literal)?;
                 // This can still fail:
-                // * During ConstProp, with `TooGeneric` or since the `requried_consts` were not all
+                // * During ConstProp, with `TooGeneric` or since the `required_consts` were not all
                 //   checked yet.
                 // * During CTFE, since promoteds in `const`/`static` initializer bodies can fail.
 
diff --git a/compiler/rustc_driver/src/lib.rs b/compiler/rustc_driver/src/lib.rs
index b36ce63dda7..43c9e9296b9 100644
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@@ -1228,7 +1228,7 @@ pub fn report_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str) {
 ///
 /// A custom rustc driver can skip calling this to set up a custom ICE hook.
 pub fn install_ice_hook() {
-    // If the user has not explicitly overriden "RUST_BACKTRACE", then produce
+    // If the user has not explicitly overridden "RUST_BACKTRACE", then produce
     // full backtraces. When a compiler ICE happens, we want to gather
     // as much information as possible to present in the issue opened
     // by the user. Compiler developers and other rustc users can
diff --git a/compiler/rustc_error_codes/src/error_codes/E0772.md b/compiler/rustc_error_codes/src/error_codes/E0772.md
index 262e52351ef..3b73abaf776 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0772.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0772.md
@@ -45,7 +45,7 @@ trait object's internal data to be accessed safely from any trait methods. This
 rule also goes for any lifetime any struct made into a trait object may have.
 
 In the implementation for `dyn Person`, the `'2` lifetime representing the
-internal data was ommitted, meaning that the compiler inferred the lifetime
+internal data was omitted, meaning that the compiler inferred the lifetime
 `'static`. As a result, the implementation's `is_cool` is inferred by the
 compiler to look like this:
 
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index 1b976180509..4af376b983c 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -1841,7 +1841,7 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
         self.flat_map_node(node)
     }
 
-    fn flat_map_stmt(&mut self, mut node: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
+    fn flat_map_stmt(&mut self, node: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
         // FIXME: invocations in semicolon-less expressions positions are expanded as expressions,
         // changing that requires some compatibility measures.
         if node.is_expr() {
@@ -1863,7 +1863,7 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
                     self.cx.current_expansion.is_trailing_mac = false;
                     res
                 }
-                _ => assign_id!(self, &mut node.id, || noop_flat_map_stmt(node, self)),
+                _ => noop_flat_map_stmt(node, self),
             };
         }
 
diff --git a/compiler/rustc_expand/src/mbe/macro_parser.rs b/compiler/rustc_expand/src/mbe/macro_parser.rs
index a419612e315..bb36dfd793d 100644
--- a/compiler/rustc_expand/src/mbe/macro_parser.rs
+++ b/compiler/rustc_expand/src/mbe/macro_parser.rs
@@ -154,7 +154,7 @@ type NamedMatchVec = SmallVec<[NamedMatch; 4]>;
 /// lifetime. By separating `'tt` from `'root`, we can show that.
 #[derive(Clone)]
 struct MatcherPos<'root, 'tt> {
-    /// The token or sequence of tokens that make up the matcher
+    /// The token or sequence of tokens that make up the matcher. `elts` is short for "elements".
     top_elts: TokenTreeOrTokenTreeSlice<'tt>,
 
     /// The position of the "dot" in this matcher
@@ -184,17 +184,8 @@ struct MatcherPos<'root, 'tt> {
     /// in this matcher.
     match_hi: usize,
 
-    // The following fields are used if we are matching a repetition. If we aren't, they should be
-    // `None`.
-    /// The KleeneOp of this sequence if we are in a repetition.
-    seq_op: Option<mbe::KleeneOp>,
-
-    /// The separator if we are in a repetition.
-    sep: Option<Token>,
-
-    /// The "parent" matcher position if we are in a repetition. That is, the matcher position just
-    /// before we enter the sequence.
-    up: Option<MatcherPosHandle<'root, 'tt>>,
+    /// This field is only used if we are matching a repetition.
+    repetition: Option<MatcherPosRepetition<'root, 'tt>>,
 
     /// Specifically used to "unzip" token trees. By "unzip", we mean to unwrap the delimiters from
     /// a delimited token tree (e.g., something wrapped in `(` `)`) or to get the contents of a doc
@@ -207,7 +198,38 @@ struct MatcherPos<'root, 'tt> {
     stack: SmallVec<[MatcherTtFrame<'tt>; 1]>,
 }
 
+// This type is used a lot. Make sure it doesn't unintentionally get bigger.
+#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+rustc_data_structures::static_assert_size!(MatcherPos<'_, '_>, 192);
+
 impl<'root, 'tt> MatcherPos<'root, 'tt> {
+    /// Generates the top-level matcher position in which the "dot" is before the first token of
+    /// the matcher `ms`.
+    fn new(ms: &'tt [TokenTree]) -> Self {
+        let match_idx_hi = count_names(ms);
+        MatcherPos {
+            // Start with the top level matcher given to us.
+            top_elts: TtSeq(ms),
+
+            // The "dot" is before the first token of the matcher.
+            idx: 0,
+
+            // Initialize `matches` to a bunch of empty `Vec`s -- one for each metavar in
+            // `top_elts`. `match_lo` for `top_elts` is 0 and `match_hi` is `match_idx_hi`.
+            // `match_cur` is 0 since we haven't actually matched anything yet.
+            matches: create_matches(match_idx_hi),
+            match_lo: 0,
+            match_cur: 0,
+            match_hi: match_idx_hi,
+
+            // Haven't descended into any delimiters, so this is empty.
+            stack: smallvec![],
+
+            // Haven't descended into any sequences, so this is `None`.
+            repetition: None,
+        }
+    }
+
     /// Adds `m` as a named match for the `idx`-th metavar.
     fn push_match(&mut self, idx: usize, m: NamedMatch) {
         let matches = Lrc::make_mut(&mut self.matches[idx]);
@@ -215,6 +237,19 @@ impl<'root, 'tt> MatcherPos<'root, 'tt> {
     }
 }
 
+#[derive(Clone)]
+struct MatcherPosRepetition<'root, 'tt> {
+    /// The KleeneOp of this sequence.
+    seq_op: mbe::KleeneOp,
+
+    /// The separator.
+    sep: Option<Token>,
+
+    /// The "parent" matcher position. That is, the matcher position just before we enter the
+    /// sequence.
+    up: MatcherPosHandle<'root, 'tt>,
+}
+
 // Lots of MatcherPos instances are created at runtime. Allocating them on the
 // heap is slow. Furthermore, using SmallVec<MatcherPos> to allocate them all
 // on the stack is also slow, because MatcherPos is quite a large type and
@@ -258,6 +293,12 @@ impl<'root, 'tt> DerefMut for MatcherPosHandle<'root, 'tt> {
     }
 }
 
+enum EofItems<'root, 'tt> {
+    None,
+    One(MatcherPosHandle<'root, 'tt>),
+    Multiple,
+}
+
 /// Represents the possible results of an attempted parse.
 crate enum ParseResult<T> {
     /// Parsed successfully.
@@ -300,35 +341,6 @@ fn create_matches(len: usize) -> Box<[Lrc<NamedMatchVec>]> {
     .into_boxed_slice()
 }
 
-/// Generates the top-level matcher position in which the "dot" is before the first token of the
-/// matcher `ms`.
-fn initial_matcher_pos<'root, 'tt>(ms: &'tt [TokenTree]) -> MatcherPos<'root, 'tt> {
-    let match_idx_hi = count_names(ms);
-    let matches = create_matches(match_idx_hi);
-    MatcherPos {
-        // Start with the top level matcher given to us
-        top_elts: TtSeq(ms), // "elts" is an abbr. for "elements"
-        // The "dot" is before the first token of the matcher
-        idx: 0,
-
-        // Initialize `matches` to a bunch of empty `Vec`s -- one for each metavar in `top_elts`.
-        // `match_lo` for `top_elts` is 0 and `match_hi` is `matches.len()`. `match_cur` is 0 since
-        // we haven't actually matched anything yet.
-        matches,
-        match_lo: 0,
-        match_cur: 0,
-        match_hi: match_idx_hi,
-
-        // Haven't descended into any delimiters, so empty stack
-        stack: smallvec![],
-
-        // Haven't descended into any sequences, so both of these are `None`.
-        seq_op: None,
-        sep: None,
-        up: None,
-    }
-}
-
 /// `NamedMatch` is a pattern-match result for a single `token::MATCH_NONTERMINAL`:
 /// so it is associated with a single ident in a parse, and all
 /// `MatchedNonterminal`s in the `NamedMatch` have the same non-terminal type
@@ -475,10 +487,10 @@ fn inner_parse_loop<'root, 'tt>(
     sess: &ParseSess,
     cur_items: &mut SmallVec<[MatcherPosHandle<'root, 'tt>; 1]>,
     next_items: &mut Vec<MatcherPosHandle<'root, 'tt>>,
-    eof_items: &mut SmallVec<[MatcherPosHandle<'root, 'tt>; 1]>,
     bb_items: &mut SmallVec<[MatcherPosHandle<'root, 'tt>; 1]>,
+    eof_items: &mut EofItems<'root, 'tt>,
     token: &Token,
-) -> ParseResult<()> {
+) -> Result<(), (rustc_span::Span, String)> {
     // Pop items from `cur_items` until it is empty.
     while let Some(mut item) = cur_items.pop() {
         // When unzipped trees end, remove them. This corresponds to backtracking out of a
@@ -504,7 +516,7 @@ fn inner_parse_loop<'root, 'tt>(
             // We are repeating iff there is a parent. If the matcher is inside of a repetition,
             // then we could be at the end of a sequence or at the beginning of the next
             // repetition.
-            if item.up.is_some() {
+            if let Some(repetition) = &item.repetition {
                 // At this point, regardless of whether there is a separator, we should add all
                 // matches from the complete repetition of the sequence to the shared, top-level
                 // `matches` list (actually, `up.matches`, which could itself not be the top-level,
@@ -515,7 +527,7 @@ fn inner_parse_loop<'root, 'tt>(
                 // NOTE: removing the condition `idx == len` allows trailing separators.
                 if idx == len {
                     // Get the `up` matcher
-                    let mut new_pos = item.up.clone().unwrap();
+                    let mut new_pos = repetition.up.clone();
 
                     // Add matches from this repetition to the `matches` of `up`
                     for idx in item.match_lo..item.match_hi {
@@ -530,32 +542,33 @@ fn inner_parse_loop<'root, 'tt>(
                 }
 
                 // Check if we need a separator.
-                if idx == len && item.sep.is_some() {
+                if idx == len && repetition.sep.is_some() {
                     // We have a separator, and it is the current token. We can advance past the
                     // separator token.
-                    if item.sep.as_ref().map_or(false, |sep| token_name_eq(token, sep)) {
+                    if repetition.sep.as_ref().map_or(false, |sep| token_name_eq(token, sep)) {
                         item.idx += 1;
                         next_items.push(item);
                     }
-                }
-                // We don't need a separator. Move the "dot" back to the beginning of the matcher
-                // and try to match again UNLESS we are only allowed to have _one_ repetition.
-                else if item.seq_op != Some(mbe::KleeneOp::ZeroOrOne) {
+                } else if repetition.seq_op != mbe::KleeneOp::ZeroOrOne {
+                    // We don't need a separator. Move the "dot" back to the beginning of the
+                    // matcher and try to match again UNLESS we are only allowed to have _one_
+                    // repetition.
                     item.match_cur = item.match_lo;
                     item.idx = 0;
                     cur_items.push(item);
                 }
+            } else {
+                // If we are not in a repetition, then being at the end of a matcher means that we
+                // have reached the potential end of the input.
+                *eof_items = match eof_items {
+                    EofItems::None => EofItems::One(item),
+                    EofItems::One(_) | EofItems::Multiple => EofItems::Multiple,
+                }
             }
-            // If we are not in a repetition, then being at the end of a matcher means that we have
-            // reached the potential end of the input.
-            else {
-                eof_items.push(item);
-            }
-        }
-        // We are in the middle of a matcher.
-        else {
-            // Look at what token in the matcher we are trying to match the current token (`token`)
-            // against. Depending on that, we may generate new items.
+        } else {
+            // We are in the middle of a matcher. Look at what token in the matcher we are trying
+            // to match the current token (`token`) against. Depending on that, we may generate new
+            // items.
             match item.top_elts.get_tt(idx) {
                 // Need to descend into a sequence
                 TokenTree::Sequence(sp, seq) => {
@@ -578,14 +591,16 @@ fn inner_parse_loop<'root, 'tt>(
                     let matches = create_matches(item.matches.len());
                     cur_items.push(MatcherPosHandle::Box(Box::new(MatcherPos {
                         stack: smallvec![],
-                        sep: seq.separator.clone(),
-                        seq_op: Some(seq.kleene.op),
                         idx: 0,
                         matches,
                         match_lo: item.match_cur,
                         match_cur: item.match_cur,
                         match_hi: item.match_cur + seq.num_captures,
-                        up: Some(item),
+                        repetition: Some(MatcherPosRepetition {
+                            up: item,
+                            sep: seq.separator.clone(),
+                            seq_op: seq.kleene.op,
+                        }),
                         top_elts: Tt(TokenTree::Sequence(sp, seq)),
                     })));
                 }
@@ -593,7 +608,7 @@ fn inner_parse_loop<'root, 'tt>(
                 // We need to match a metavar (but the identifier is invalid)... this is an error
                 TokenTree::MetaVarDecl(span, _, None) => {
                     if sess.missing_fragment_specifiers.borrow_mut().remove(&span).is_some() {
-                        return Error(span, "missing fragment specifier".to_string());
+                        return Err((span, "missing fragment specifier".to_string()));
                     }
                 }
 
@@ -641,7 +656,7 @@ fn inner_parse_loop<'root, 'tt>(
     }
 
     // Yay a successful parse (so far)!
-    Success(())
+    Ok(())
 }
 
 /// Use the given sequence of token trees (`ms`) as a matcher. Match the token
@@ -659,17 +674,18 @@ pub(super) fn parse_tt(
     //
     // This MatcherPos instance is allocated on the stack. All others -- and
     // there are frequently *no* others! -- are allocated on the heap.
-    let mut initial = initial_matcher_pos(ms);
+    let mut initial = MatcherPos::new(ms);
     let mut cur_items = smallvec![MatcherPosHandle::Ref(&mut initial)];
     let mut next_items = Vec::new();
 
     loop {
+        assert!(next_items.is_empty());
+
         // Matcher positions black-box parsed by parser.rs (`parser`)
         let mut bb_items = SmallVec::new();
 
         // Matcher positions that would be valid if the macro invocation was over now
-        let mut eof_items = SmallVec::new();
-        assert!(next_items.is_empty());
+        let mut eof_items = EofItems::None;
 
         // Process `cur_items` until either we have finished the input or we need to get some
         // parsing from the black-box parser done. The result is that `next_items` will contain a
@@ -678,37 +694,34 @@ pub(super) fn parse_tt(
             parser.sess,
             &mut cur_items,
             &mut next_items,
-            &mut eof_items,
             &mut bb_items,
+            &mut eof_items,
             &parser.token,
         ) {
-            Success(_) => {}
-            Failure(token, msg) => return Failure(token, msg),
-            Error(sp, msg) => return Error(sp, msg),
-            ErrorReported => return ErrorReported,
+            Ok(()) => {}
+            Err((sp, msg)) => return Error(sp, msg),
         }
 
         // inner parse loop handled all cur_items, so it's empty
         assert!(cur_items.is_empty());
 
-        // We need to do some post processing after the `inner_parser_loop`.
+        // We need to do some post processing after the `inner_parse_loop`.
         //
         // Error messages here could be improved with links to original rules.
 
         // If we reached the EOF, check that there is EXACTLY ONE possible matcher. Otherwise,
         // either the parse is ambiguous (which should never happen) or there is a syntax error.
         if parser.token == token::Eof {
-            if eof_items.len() == 1 {
-                let matches =
-                    eof_items[0].matches.iter_mut().map(|dv| Lrc::make_mut(dv).pop().unwrap());
-                return nameize(parser.sess, ms, matches);
-            } else if eof_items.len() > 1 {
-                return Error(
-                    parser.token.span,
-                    "ambiguity: multiple successful parses".to_string(),
-                );
-            } else {
-                return Failure(
+            return match eof_items {
+                EofItems::One(mut eof_item) => {
+                    let matches =
+                        eof_item.matches.iter_mut().map(|dv| Lrc::make_mut(dv).pop().unwrap());
+                    nameize(parser.sess, ms, matches)
+                }
+                EofItems::Multiple => {
+                    Error(parser.token.span, "ambiguity: multiple successful parses".to_string())
+                }
+                EofItems::None => Failure(
                     Token::new(
                         token::Eof,
                         if parser.token.span.is_dummy() {
@@ -718,12 +731,12 @@ pub(super) fn parse_tt(
                         },
                     ),
                     "missing tokens in macro arguments",
-                );
-            }
+                ),
+            };
         }
-        // Performance hack: eof_items may share matchers via Rc with other things that we want
-        // to modify. Dropping eof_items now may drop these refcounts to 1, preventing an
-        // unnecessary implicit clone later in Rc::make_mut.
+        // Performance hack: `eof_items` may share matchers via `Rc` with other things that we want
+        // to modify. Dropping `eof_items` now may drop these refcounts to 1, preventing an
+        // unnecessary implicit clone later in `Rc::make_mut`.
         drop(eof_items);
 
         // If there are no possible next positions AND we aren't waiting for the black-box parser,
@@ -731,9 +744,10 @@ pub(super) fn parse_tt(
         if bb_items.is_empty() && next_items.is_empty() {
             return Failure(parser.token.clone(), "no rules expected this token in macro call");
         }
-        // Another possibility is that we need to call out to parse some rust nonterminal
-        // (black-box) parser. However, if there is not EXACTLY ONE of these, something is wrong.
-        else if (!bb_items.is_empty() && !next_items.is_empty()) || bb_items.len() > 1 {
+
+        if (!bb_items.is_empty() && !next_items.is_empty()) || bb_items.len() > 1 {
+            // We need to call out to parse some rust nonterminal (black-box) parser. But something
+            // is wrong, because there is not EXACTLY ONE of these.
             let nts = bb_items
                 .iter()
                 .map(|item| match item.top_elts.get_tt(item.idx) {
@@ -755,15 +769,15 @@ pub(super) fn parse_tt(
                 ),
             );
         }
-        // Dump all possible `next_items` into `cur_items` for the next iteration.
-        else if !next_items.is_empty() {
-            // Now process the next token
+
+        if !next_items.is_empty() {
+            // Dump all possible `next_items` into `cur_items` for the next iteration. Then process
+            // the next token.
             cur_items.extend(next_items.drain(..));
             parser.to_mut().bump();
-        }
-        // Finally, we have the case where we need to call the black-box parser to get some
-        // nonterminal.
-        else {
+        } else {
+            // Finally, we have the case where we need to call the black-box parser to get some
+            // nonterminal.
             assert_eq!(bb_items.len(), 1);
 
             let mut item = bb_items.pop().unwrap();
diff --git a/compiler/rustc_expand/src/mbe/transcribe.rs b/compiler/rustc_expand/src/mbe/transcribe.rs
index 54000527c15..760dea77f9c 100644
--- a/compiler/rustc_expand/src/mbe/transcribe.rs
+++ b/compiler/rustc_expand/src/mbe/transcribe.rs
@@ -233,7 +233,7 @@ pub(super) fn transcribe<'a>(
                         } else {
                             // Other variables are emitted into the output stream as groups with
                             // `Delimiter::None` to maintain parsing priorities.
-                            // `Interpolated` is currenty used for such groups in rustc parser.
+                            // `Interpolated` is currently used for such groups in rustc parser.
                             marker.visit_span(&mut sp);
                             TokenTree::token(token::Interpolated(nt.clone()), sp)
                         };
diff --git a/compiler/rustc_expand/src/proc_macro_server.rs b/compiler/rustc_expand/src/proc_macro_server.rs
index 869cada400f..0aef5982cff 100644
--- a/compiler/rustc_expand/src/proc_macro_server.rs
+++ b/compiler/rustc_expand/src/proc_macro_server.rs
@@ -847,7 +847,7 @@ impl server::Span for Rustc<'_, '_> {
     /// the `quote` proc-macro. This will save the span of
     /// "hello" into the metadata of `my_proc_macro`. As a result,
     /// the body of `my_proc_macro` (after expansion) will end
-    /// up containg a call that looks like this:
+    /// up containing a call that looks like this:
     /// `proc_macro::Ident::new("hello", proc_macro::Span::recover_proc_macro_span(0))`
     ///
     /// where `0` is the id returned by this function.
diff --git a/compiler/rustc_incremental/src/persist/load.rs b/compiler/rustc_incremental/src/persist/load.rs
index 870c3f80682..908a9361424 100644
--- a/compiler/rustc_incremental/src/persist/load.rs
+++ b/compiler/rustc_incremental/src/persist/load.rs
@@ -27,7 +27,7 @@ pub enum LoadResult<T> {
     },
     /// The file either didn't exist or was produced by an incompatible compiler version.
     DataOutOfDate,
-    /// An error occured.
+    /// An error occurred.
     Error {
         #[allow(missing_docs)]
         message: String,
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 3bc30f0220d..16f7504cbbe 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
@@ -928,7 +928,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 /// performing that replacement, we'll turn all remaining infer type params to use their name from
 /// their definition, and replace all the `[type error]`s back to being infer so they display in
 /// the output as `_`. If we didn't go through `[type error]`, we would either show all type params
-/// by their name *or* `_`, neither of which is desireable: we want to show all types that we could
+/// by their name *or* `_`, neither of which is desirable: we want to show all types that we could
 /// infer as `_` to reduce verbosity and avoid telling the user about unnecessary type annotations.
 struct ResolvedTypeParamEraser<'tcx> {
     tcx: TyCtxt<'tcx>,
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mismatched_static_lifetime.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mismatched_static_lifetime.rs
index e0420291aa3..4710eae6189 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mismatched_static_lifetime.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mismatched_static_lifetime.rs
@@ -58,7 +58,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                 bug!("Node not an impl.");
             };
 
-            // Next, let's figure out the set of trait objects with implict static bounds
+            // Next, let's figure out the set of trait objects with implicit static bounds
             let ty = self.tcx().type_of(*impl_def_id);
             let mut v = super::static_impl_trait::TraitObjectVisitor(FxHashSet::default());
             v.visit_ty(ty);
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index c3e168c4727..06f73c1c916 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -26,7 +26,7 @@ use rustc_middle::mir::interpret;
 use rustc_middle::thir;
 use rustc_middle::traits::specialization_graph;
 use rustc_middle::ty::codec::TyEncoder;
-use rustc_middle::ty::fast_reject::{self, SimplifiedType, SimplifyParams};
+use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, SymbolName, Ty, TyCtxt};
 use rustc_serialize::{opaque, Encodable, Encoder};
@@ -2043,7 +2043,7 @@ impl<'tcx, 'v> ItemLikeVisitor<'v> for ImplsVisitor<'tcx> {
                     let simplified_self_ty = fast_reject::simplify_type(
                         self.tcx,
                         trait_ref.self_ty(),
-                        SimplifyParams::No,
+                        TreatParams::AsPlaceholders,
                     );
 
                     self.impls
diff --git a/compiler/rustc_middle/src/ty/fast_reject.rs b/compiler/rustc_middle/src/ty/fast_reject.rs
index 3c1ac66e2d1..c0dd4db2945 100644
--- a/compiler/rustc_middle/src/ty/fast_reject.rs
+++ b/compiler/rustc_middle/src/ty/fast_reject.rs
@@ -49,9 +49,14 @@ where
 }
 
 #[derive(PartialEq, Eq, Debug, Clone, Copy)]
-pub enum SimplifyParams {
-    Yes,
-    No,
+pub enum TreatParams {
+    /// Treat parameters as bound types in the given environment.
+    ///
+    /// For this to be correct the input has to be fully normalized
+    /// in its param env as it may otherwise cause us to ignore
+    /// potentially applying impls.
+    AsBoundTypes,
+    AsPlaceholders,
 }
 
 /// Tries to simplify a type by only returning the outermost injective¹ layer, if one exists.
@@ -59,26 +64,21 @@ pub enum SimplifyParams {
 /// The idea is to get something simple that we can use to quickly decide if two types could unify,
 /// for example during method lookup.
 ///
-/// A special case here are parameters and projections. Projections can be normalized to
-/// a different type, meaning that `<T as Trait>::Assoc` and `u8` can be unified, even though
-/// their outermost layer is different while parameters like `T` of impls are later replaced
-/// with an inference variable, which then also allows unification with other types.
+/// A special case here are parameters and projections, which are only injective
+/// if they are treated as bound types.
 ///
-/// When using `SimplifyParams::Yes`, we still return a simplified type for params and projections²,
-/// the reasoning for this can be seen at the places doing this.
+/// For example when storing impls based on their simplified self type, we treat
+/// generic parameters as placeholders. We must not simplify them here,
+/// as they can unify with any other type.
 ///
+/// With projections we have to be even more careful, as even when treating them as bound types
+/// this is still only correct if they are fully normalized.
 ///
-/// ¹ meaning that if two outermost layers are different, then the whole types are also different.
-/// ² FIXME(@lcnr): this seems like it can actually end up being unsound with the way it's used during
-///   candidate selection. We do not consider non blanket impls for `<_ as Trait>::Assoc` even
-///   though `_` can be inferred to a concrete type later at which point a concrete impl
-///   could actually apply. After experimenting for about an hour I wasn't able to cause any issues
-///   this way so I am not going to change this until we actually find an issue as I am really
-///   interesting in getting an actual test for this.
-pub fn simplify_type(
-    tcx: TyCtxt<'_>,
-    ty: Ty<'_>,
-    can_simplify_params: SimplifyParams,
+/// ¹ meaning that if the outermost layers are different, then the whole types are also different.
+pub fn simplify_type<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    ty: Ty<'tcx>,
+    treat_params: TreatParams,
 ) -> Option<SimplifiedType> {
     match *ty.kind() {
         ty::Bool => Some(BoolSimplifiedType),
@@ -91,7 +91,7 @@ pub fn simplify_type(
         ty::Array(..) => Some(ArraySimplifiedType),
         ty::Slice(..) => Some(SliceSimplifiedType),
         ty::RawPtr(ptr) => Some(PtrSimplifiedType(ptr.mutbl)),
-        ty::Dynamic(ref trait_info, ..) => match trait_info.principal_def_id() {
+        ty::Dynamic(trait_info, ..) => match trait_info.principal_def_id() {
             Some(principal_def_id) if !tcx.trait_is_auto(principal_def_id) => {
                 Some(TraitSimplifiedType(principal_def_id))
             }
@@ -100,24 +100,21 @@ pub fn simplify_type(
         ty::Ref(_, _, mutbl) => Some(RefSimplifiedType(mutbl)),
         ty::FnDef(def_id, _) | ty::Closure(def_id, _) => Some(ClosureSimplifiedType(def_id)),
         ty::Generator(def_id, _, _) => Some(GeneratorSimplifiedType(def_id)),
-        ty::GeneratorWitness(ref tys) => {
-            Some(GeneratorWitnessSimplifiedType(tys.skip_binder().len()))
-        }
+        ty::GeneratorWitness(tys) => Some(GeneratorWitnessSimplifiedType(tys.skip_binder().len())),
         ty::Never => Some(NeverSimplifiedType),
-        ty::Tuple(ref tys) => Some(TupleSimplifiedType(tys.len())),
-        ty::FnPtr(ref f) => Some(FunctionSimplifiedType(f.skip_binder().inputs().len())),
-        ty::Projection(_) | ty::Param(_) => {
-            if can_simplify_params == SimplifyParams::Yes {
-                // In normalized types, projections don't unify with
-                // anything. when lazy normalization happens, this
-                // will change. It would still be nice to have a way
-                // to deal with known-not-to-unify-with-anything
-                // projections (e.g., the likes of <__S as Encoder>::Error).
+        ty::Tuple(tys) => Some(TupleSimplifiedType(tys.len())),
+        ty::FnPtr(f) => Some(FunctionSimplifiedType(f.skip_binder().inputs().len())),
+        ty::Param(_) | ty::Projection(_) => match treat_params {
+            // When treated as bound types, projections don't unify with
+            // anything as long as they are fully normalized.
+            //
+            // We will have to be careful with lazy normalization here.
+            TreatParams::AsBoundTypes => {
+                debug!("treating `{}` as a bound type", ty);
                 Some(ParameterSimplifiedType)
-            } else {
-                None
             }
-        }
+            TreatParams::AsPlaceholders => None,
+        },
         ty::Opaque(def_id, _) => Some(OpaqueSimplifiedType(def_id)),
         ty::Foreign(def_id) => Some(ForeignSimplifiedType(def_id)),
         ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) | ty::Error(_) => None,
diff --git a/compiler/rustc_middle/src/ty/trait_def.rs b/compiler/rustc_middle/src/ty/trait_def.rs
index 6100eb48a18..8ebeca50c41 100644
--- a/compiler/rustc_middle/src/ty/trait_def.rs
+++ b/compiler/rustc_middle/src/ty/trait_def.rs
@@ -1,5 +1,5 @@
 use crate::traits::specialization_graph;
-use crate::ty::fast_reject::{self, SimplifiedType, SimplifyParams};
+use crate::ty::fast_reject::{self, SimplifiedType, TreatParams};
 use crate::ty::fold::TypeFoldable;
 use crate::ty::{Ident, Ty, TyCtxt};
 use rustc_hir as hir;
@@ -150,7 +150,7 @@ impl<'tcx> TyCtxt<'tcx> {
         self_ty: Ty<'tcx>,
     ) -> impl Iterator<Item = DefId> + 'tcx {
         let impls = self.trait_impls_of(def_id);
-        if let Some(simp) = fast_reject::simplify_type(self, self_ty, SimplifyParams::No) {
+        if let Some(simp) = fast_reject::simplify_type(self, self_ty, TreatParams::AsPlaceholders) {
             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
                 return impls.iter().copied();
             }
@@ -180,14 +180,14 @@ impl<'tcx> TyCtxt<'tcx> {
             }
         }
 
-        // Note that we're using `SimplifyParams::Yes` to query `non_blanket_impls` while using
-        // `SimplifyParams::No` while actually adding them.
+        // Note that we're using `TreatParams::AsBoundTypes` to query `non_blanket_impls` while using
+        // `TreatParams::AsPlaceholders` while actually adding them.
         //
         // This way, when searching for some impl for `T: Trait`, we do not look at any impls
         // whose outer level is not a parameter or projection. Especially for things like
         // `T: Clone` this is incredibly useful as we would otherwise look at all the impls
         // of `Clone` for `Option<T>`, `Vec<T>`, `ConcreteType` and so on.
-        if let Some(simp) = fast_reject::simplify_type(self, self_ty, SimplifyParams::Yes) {
+        if let Some(simp) = fast_reject::simplify_type(self, self_ty, TreatParams::AsBoundTypes) {
             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
                 for &impl_def_id in impls {
                     if let result @ Some(_) = f(impl_def_id) {
@@ -247,7 +247,7 @@ pub(super) fn trait_impls_of_provider(tcx: TyCtxt<'_>, trait_id: DefId) -> Trait
         }
 
         if let Some(simplified_self_ty) =
-            fast_reject::simplify_type(tcx, impl_self_ty, SimplifyParams::No)
+            fast_reject::simplify_type(tcx, impl_self_ty, TreatParams::AsPlaceholders)
         {
             impls.non_blanket_impls.entry(simplified_self_ty).or_default().push(impl_def_id);
         } else {
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 086f0249114..3342bd146c4 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -3207,7 +3207,7 @@ impl<'a> Resolver<'a> {
                     }
                 }
             }
-            ImportKind::ExternCrate { source, target, .. } => {
+            ImportKind::ExternCrate { source, target } => {
                 suggestion = Some(format!(
                     "extern crate {} as {};",
                     source.unwrap_or(target.name),
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index 018d1eefef7..63efa951f96 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -20,7 +20,7 @@ use rustc_hir::CRATE_HIR_ID;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::TraitEngine;
 use rustc_middle::traits::specialization_graph::OverlapMode;
-use rustc_middle::ty::fast_reject::{self, SimplifyParams};
+use rustc_middle::ty::fast_reject::{self, TreatParams};
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -87,8 +87,8 @@ where
         impl2_ref.iter().flat_map(|tref| tref.substs.types()),
     )
     .any(|(ty1, ty2)| {
-        let t1 = fast_reject::simplify_type(tcx, ty1, SimplifyParams::No);
-        let t2 = fast_reject::simplify_type(tcx, ty2, SimplifyParams::No);
+        let t1 = fast_reject::simplify_type(tcx, ty1, TreatParams::AsPlaceholders);
+        let t2 = fast_reject::simplify_type(tcx, ty2, TreatParams::AsPlaceholders);
 
         if let (Some(t1), Some(t2)) = (t1, t2) {
             // Simplified successfully
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 092ef5f11e9..8af4606db85 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -36,7 +36,7 @@ use rustc_infer::infer::LateBoundRegionConversionTime;
 use rustc_middle::dep_graph::{DepKind, DepNodeIndex};
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::thir::abstract_const::NotConstEvaluatable;
-use rustc_middle::ty::fast_reject::{self, SimplifyParams};
+use rustc_middle::ty::fast_reject::{self, TreatParams};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::relate::TypeRelation;
 use rustc_middle::ty::subst::{GenericArgKind, Subst, SubstsRef};
@@ -2176,8 +2176,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
     fn fast_reject_trait_refs(
         &mut self,
-        obligation: &TraitObligation<'_>,
-        impl_trait_ref: &ty::TraitRef<'_>,
+        obligation: &TraitObligation<'tcx>,
+        impl_trait_ref: &ty::TraitRef<'tcx>,
     ) -> bool {
         // We can avoid creating type variables and doing the full
         // substitution if we find that any of the input types, when
@@ -2193,10 +2193,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         let simplified_obligation_ty = fast_reject::simplify_type(
                             self.tcx(),
                             obligation_ty,
-                            SimplifyParams::Yes,
+                            TreatParams::AsBoundTypes,
+                        );
+                        let simplified_impl_ty = fast_reject::simplify_type(
+                            self.tcx(),
+                            impl_ty,
+                            TreatParams::AsPlaceholders,
                         );
-                        let simplified_impl_ty =
-                            fast_reject::simplify_type(self.tcx(), impl_ty, SimplifyParams::No);
 
                         simplified_obligation_ty.is_some()
                             && simplified_impl_ty.is_some()
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
index e31a9b200e8..8b23dcfe380 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
@@ -2,7 +2,7 @@ use super::OverlapError;
 
 use crate::traits;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::fast_reject::{self, SimplifiedType, SimplifyParams};
+use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
 
@@ -49,7 +49,9 @@ impl ChildrenExt<'_> for Children {
     /// Insert an impl into this set of children without comparing to any existing impls.
     fn insert_blindly(&mut self, tcx: TyCtxt<'_>, impl_def_id: DefId) {
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
-        if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), SimplifyParams::No) {
+        if let Some(st) =
+            fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsPlaceholders)
+        {
             debug!("insert_blindly: impl_def_id={:?} st={:?}", impl_def_id, st);
             self.non_blanket_impls.entry(st).or_default().push(impl_def_id)
         } else {
@@ -64,7 +66,9 @@ impl ChildrenExt<'_> for Children {
     fn remove_existing(&mut self, tcx: TyCtxt<'_>, impl_def_id: DefId) {
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
         let vec: &mut Vec<DefId>;
-        if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), SimplifyParams::No) {
+        if let Some(st) =
+            fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsPlaceholders)
+        {
             debug!("remove_existing: impl_def_id={:?} st={:?}", impl_def_id, st);
             vec = self.non_blanket_impls.get_mut(&st).unwrap();
         } else {
@@ -312,7 +316,8 @@ impl GraphExt for Graph {
 
         let mut parent = trait_def_id;
         let mut last_lint = None;
-        let simplified = fast_reject::simplify_type(tcx, trait_ref.self_ty(), SimplifyParams::No);
+        let simplified =
+            fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsPlaceholders);
 
         // Descend the specialization tree, where `parent` is the current parent node.
         loop {
diff --git a/compiler/rustc_typeck/src/check/method/suggest.rs b/compiler/rustc_typeck/src/check/method/suggest.rs
index 1a345a303ca..0ae2dfa180b 100644
--- a/compiler/rustc_typeck/src/check/method/suggest.rs
+++ b/compiler/rustc_typeck/src/check/method/suggest.rs
@@ -12,7 +12,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_hir::{ExprKind, Node, QPath};
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_middle::traits::util::supertraits;
-use rustc_middle::ty::fast_reject::{simplify_type, SimplifyParams};
+use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
 use rustc_middle::ty::print::with_crate_prefix;
 use rustc_middle::ty::ToPolyTraitRef;
 use rustc_middle::ty::{self, DefIdTree, ToPredicate, Ty, TyCtxt, TypeFoldable};
@@ -1777,7 +1777,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // FIXME: Even though negative bounds are not implemented, we could maybe handle
                 // cases where a positive bound implies a negative impl.
                 (candidates, Vec::new())
-            } else if let Some(simp_rcvr_ty) = simplify_type(self.tcx, rcvr_ty, SimplifyParams::Yes)
+            } else if let Some(simp_rcvr_ty) =
+                simplify_type(self.tcx, rcvr_ty, TreatParams::AsBoundTypes)
             {
                 let mut potential_candidates = Vec::new();
                 let mut explicitly_negative = Vec::new();
@@ -1792,7 +1793,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         .any(|imp_did| {
                             let imp = self.tcx.impl_trait_ref(imp_did).unwrap();
                             let imp_simp =
-                                simplify_type(self.tcx, imp.self_ty(), SimplifyParams::Yes);
+                                simplify_type(self.tcx, imp.self_ty(), TreatParams::AsBoundTypes);
                             imp_simp.map_or(false, |s| s == simp_rcvr_ty)
                         })
                     {
diff --git a/library/core/src/iter/adapters/map.rs b/library/core/src/iter/adapters/map.rs
index b2ed82508dd..d2077a63e15 100644
--- a/library/core/src/iter/adapters/map.rs
+++ b/library/core/src/iter/adapters/map.rs
@@ -38,7 +38,7 @@ use crate::ops::Try;
 /// }
 /// ```
 ///
-/// This will print "('a', 1), ('b', 2), ('c', 3)".
+/// This will print `('a', 1), ('b', 2), ('c', 3)`.
 ///
 /// Now consider this twist where we add a call to `rev`. This version will
 /// print `('c', 1), ('b', 2), ('a', 3)`. Note that the letters are reversed,
diff --git a/library/std/src/sys/unix/thread.rs b/library/std/src/sys/unix/thread.rs
index cf8cf5ad49f..ff01ce27333 100644
--- a/library/std/src/sys/unix/thread.rs
+++ b/library/std/src/sys/unix/thread.rs
@@ -279,10 +279,15 @@ pub fn available_parallelism() -> io::Result<NonZeroUsize> {
         ))] {
             #[cfg(any(target_os = "android", target_os = "linux"))]
             {
+                let quota = cgroup2_quota().max(1);
                 let mut set: libc::cpu_set_t = unsafe { mem::zeroed() };
-                if unsafe { libc::sched_getaffinity(0, mem::size_of::<libc::cpu_set_t>(), &mut set) } == 0 {
-                    let count = unsafe { libc::CPU_COUNT(&set) };
-                    return Ok(unsafe { NonZeroUsize::new_unchecked(count as usize) });
+                unsafe {
+                    if libc::sched_getaffinity(0, mem::size_of::<libc::cpu_set_t>(), &mut set) == 0 {
+                        let count = libc::CPU_COUNT(&set) as usize;
+                        let count = count.min(quota);
+                        // SAFETY: affinity mask can't be empty and the quota gets clamped to a minimum of 1
+                        return Ok(NonZeroUsize::new_unchecked(count));
+                    }
                 }
             }
             match unsafe { libc::sysconf(libc::_SC_NPROCESSORS_ONLN) } {
@@ -368,6 +373,80 @@ pub fn available_parallelism() -> io::Result<NonZeroUsize> {
     }
 }
 
+/// Returns cgroup CPU quota in core-equivalents, rounded down, or usize::MAX if the quota cannot
+/// be determined or is not set.
+#[cfg(any(target_os = "android", target_os = "linux"))]
+fn cgroup2_quota() -> usize {
+    use crate::ffi::OsString;
+    use crate::fs::{try_exists, File};
+    use crate::io::Read;
+    use crate::os::unix::ffi::OsStringExt;
+    use crate::path::PathBuf;
+
+    let mut quota = usize::MAX;
+
+    let _: Option<()> = try {
+        let mut buf = Vec::with_capacity(128);
+        // find our place in the cgroup hierarchy
+        File::open("/proc/self/cgroup").ok()?.read_to_end(&mut buf).ok()?;
+        let cgroup_path = buf
+            .split(|&c| c == b'\n')
+            .filter_map(|line| {
+                let mut fields = line.splitn(3, |&c| c == b':');
+                // expect cgroupv2 which has an empty 2nd field
+                if fields.nth(1) != Some(b"") {
+                    return None;
+                }
+                let path = fields.last()?;
+                // skip leading slash
+                Some(path[1..].to_owned())
+            })
+            .next()?;
+        let cgroup_path = PathBuf::from(OsString::from_vec(cgroup_path));
+
+        let mut path = PathBuf::with_capacity(128);
+        let mut read_buf = String::with_capacity(20);
+
+        let cgroup_mount = "/sys/fs/cgroup";
+
+        path.push(cgroup_mount);
+        path.push(&cgroup_path);
+
+        path.push("cgroup.controllers");
+
+        // skip if we're not looking at cgroup2
+        if matches!(try_exists(&path), Err(_) | Ok(false)) {
+            return usize::MAX;
+        };
+
+        path.pop();
+
+        while path.starts_with(cgroup_mount) {
+            path.push("cpu.max");
+
+            read_buf.clear();
+
+            if File::open(&path).and_then(|mut f| f.read_to_string(&mut read_buf)).is_ok() {
+                let raw_quota = read_buf.lines().next()?;
+                let mut raw_quota = raw_quota.split(' ');
+                let limit = raw_quota.next()?;
+                let period = raw_quota.next()?;
+                match (limit.parse::<usize>(), period.parse::<usize>()) {
+                    (Ok(limit), Ok(period)) => {
+                        quota = quota.min(limit / period);
+                    }
+                    _ => {}
+                }
+            }
+
+            path.pop(); // pop filename
+            path.pop(); // pop dir
+        }
+    };
+
+    quota
+}
+
 #[cfg(all(
     not(target_os = "linux"),
     not(target_os = "freebsd"),
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index beb60609934..09d1e714ab6 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -1524,7 +1524,10 @@ fn _assert_sync_and_send() {
 ///
 /// On Linux:
 /// - It may overcount the amount of parallelism available when limited by a
-///   process-wide affinity mask, or when affected by cgroup limits.
+///   process-wide affinity mask or cgroup quotas and cgroup2 fs or `sched_getaffinity()` can't be
+///   queried, e.g. due to sandboxing.
+/// - It may undercount the amount of parallelism if the current thread's affinity mask
+///   does not reflect the process' cpuset, e.g. due to pinned threads.
 ///
 /// On all targets:
 /// - It may overcount the amount of parallelism available when running in a VM
diff --git a/src/test/rustdoc/macro-higher-kinded-function.rs b/src/test/rustdoc/macro-higher-kinded-function.rs
new file mode 100644
index 00000000000..02a4305644e
--- /dev/null
+++ b/src/test/rustdoc/macro-higher-kinded-function.rs
@@ -0,0 +1,21 @@
+#![crate_name = "foo"]
+
+pub struct TyCtxt<'tcx>(&'tcx u8);
+
+macro_rules! gen {
+    ($(($name:ident, $tcx:lifetime, [$k:ty], [$r:ty]))*) => {
+        pub struct Providers {
+            $(pub $name: for<$tcx> fn(TyCtxt<$tcx>, $k) -> $r,)*
+        }
+    }
+}
+
+// @has 'foo/struct.Providers.html'
+// @has - '//*[@class="docblock item-decl"]//code' "pub a: for<'tcx> fn(_: TyCtxt<'tcx>, _: u8) -> i8,"
+// @has - '//*[@class="docblock item-decl"]//code' "pub b: for<'tcx> fn(_: TyCtxt<'tcx>, _: u16) -> i16,"
+// @has - '//*[@id="structfield.a"]/code' "a: for<'tcx> fn(_: TyCtxt<'tcx>, _: u8) -> i8"
+// @has - '//*[@id="structfield.b"]/code' "b: for<'tcx> fn(_: TyCtxt<'tcx>, _: u16) -> i16"
+gen! {
+    (a, 'tcx, [u8], [i8])
+    (b, 'tcx, [u16], [i16])
+}
diff --git a/src/test/ui/check-cfg/stmt-no-ice.rs b/src/test/ui/check-cfg/stmt-no-ice.rs
new file mode 100644
index 00000000000..cf76487ed46
--- /dev/null
+++ b/src/test/ui/check-cfg/stmt-no-ice.rs
@@ -0,0 +1,10 @@
+// This test checks that there is no ICE with this code
+//
+// check-pass
+// compile-flags:--check-cfg=names() -Z unstable-options
+
+fn main() {
+    #[cfg(crossbeam_loom)]
+    //~^ WARNING unexpected `cfg` condition name
+    {}
+}
diff --git a/src/test/ui/check-cfg/stmt-no-ice.stderr b/src/test/ui/check-cfg/stmt-no-ice.stderr
new file mode 100644
index 00000000000..da65b596911
--- /dev/null
+++ b/src/test/ui/check-cfg/stmt-no-ice.stderr
@@ -0,0 +1,10 @@
+warning: unexpected `cfg` condition name
+  --> $DIR/stmt-no-ice.rs:7:11
+   |
+LL |     #[cfg(crossbeam_loom)]
+   |           ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(unexpected_cfgs)]` on by default
+
+warning: 1 warning emitted
+