Auto merge of #124646 - matthiaskrgr:rollup-crlsvg5, r=matthiaskrgr

Rollup of 10 pull requests

Successful merges:

 - #123480 (deref patterns: impl `DerefPure` for more std types)
 - #124412 (io safety: update Unix explanation to use `Arc`)
 - #124441 (String.truncate comment microfix (greater or equal))
 - #124594 (run-make-support: preserve tooks.mk behavior for EXTRACXXFLAGS)
 - #124604 (library/std: Remove unused `gimli-symbolize` feature)
 - #124607 (`rustc_expand` cleanups)
 - #124609 (variable-precision float operations can differ depending on optimization levels)
 - #124610 (Tweak `consts_may_unify`)
 - #124626 (const_eval_select: add tracking issue)
 - #124637 (AST pretty: Use `builtin_syntax` for type ascription)

Failed merges:

 - #124638 (Move some tests from `rustc_expand` to `rustc_parse`.)

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

Author: bors

compiler/rustc_ast/src/ast.rs

@@ -1390,7 +1390,7 @@ pub struct StructExpr {
 // Adding a new variant? Please update `test_expr` in `tests/ui/macros/stringify.rs`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum ExprKind {
-    /// An array (`[a, b, c, d]`)
+    /// An array (e.g, `[a, b, c, d]`).
     Array(ThinVec<P<Expr>>),
     /// Allow anonymous constants from an inline `const` block
     ConstBlock(AnonConst),
@@ -1401,7 +1401,7 @@ pub enum ExprKind {
     /// This also represents calling the constructor of
     /// tuple-like ADTs such as tuple structs and enum variants.
     Call(P<Expr>, ThinVec<P<Expr>>),
-    /// A method call (e.g. `x.foo::<Bar, Baz>(a, b, c)`).
+    /// A method call (e.g., `x.foo::<Bar, Baz>(a, b, c)`).
     MethodCall(Box<MethodCall>),
     /// A tuple (e.g., `(a, b, c, d)`).
     Tup(ThinVec<P<Expr>>),
@@ -1413,7 +1413,10 @@ pub enum ExprKind {
     Lit(token::Lit),
     /// A cast (e.g., `foo as f64`).
     Cast(P<Expr>, P<Ty>),
-    /// A type ascription (e.g., `42: usize`).
+    /// A type ascription (e.g., `builtin # type_ascribe(42, usize)`).
+    ///
+    /// Usually not written directly in user code but
+    /// indirectly via the macro `type_ascribe!(...)`.
     Type(P<Expr>, P<Ty>),
     /// A `let pat = expr` expression that is only semantically allowed in the condition
     /// of `if` / `while` expressions. (e.g., `if let 0 = x { .. }`).
@@ -1488,7 +1491,10 @@ pub enum ExprKind {
     /// Output of the `asm!()` macro.
     InlineAsm(P<InlineAsm>),
 
-    /// Output of the `offset_of!()` macro.
+    /// An `offset_of` expression (e.g., `builtin # offset_of(Struct, field)`).
+    ///
+    /// Usually not written directly in user code but
+    /// indirectly via the macro `core::mem::offset_of!(...)`.
     OffsetOf(P<Ty>, P<[Ident]>),
 
     /// A macro invocation; pre-expansion.

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -422,7 +422,8 @@ impl<'a> State<'a> {
                 self.print_type(ty);
             }
             ast::ExprKind::Type(expr, ty) => {
-                self.word("type_ascribe!(");
+                self.word("builtin # type_ascribe");
+                self.popen();
                 self.ibox(0);
                 self.print_expr(expr, FixupContext::default());
 
@@ -431,7 +432,7 @@ impl<'a> State<'a> {
                 self.print_type(ty);
 
                 self.end();
-                self.word(")");
+                self.pclose();
             }
             ast::ExprKind::Let(pat, scrutinee, _, _) => {
                 self.print_let(pat, scrutinee, fixup);
@@ -657,15 +658,15 @@ impl<'a> State<'a> {
                 );
             }
             ast::ExprKind::InlineAsm(a) => {
-                // FIXME: This should have its own syntax, distinct from a macro invocation.
+                // FIXME: Print `builtin # asm` once macro `asm` uses `builtin_syntax`.
                 self.word("asm!");
                 self.print_inline_asm(a);
             }
             ast::ExprKind::FormatArgs(fmt) => {
-                // FIXME: This should have its own syntax, distinct from a macro invocation.
+                // FIXME: Print `builtin # format_args` once macro `format_args` uses `builtin_syntax`.
                 self.word("format_args!");
                 self.popen();
-                self.rbox(0, Inconsistent);
+                self.ibox(0);
                 self.word(reconstruct_format_args_template_string(&fmt.template));
                 for arg in fmt.arguments.all_args() {
                     self.word_space(",");
@@ -677,7 +678,7 @@ impl<'a> State<'a> {
             ast::ExprKind::OffsetOf(container, fields) => {
                 self.word("builtin # offset_of");
                 self.popen();
-                self.rbox(0, Inconsistent);
+                self.ibox(0);
                 self.print_type(container);
                 self.word(",");
                 self.space();
@@ -690,8 +691,8 @@ impl<'a> State<'a> {
                         self.print_ident(field);
                     }
                 }
-                self.pclose();
                 self.end();
+                self.pclose();
             }
             ast::ExprKind::MacCall(m) => self.print_mac(m),
             ast::ExprKind::Paren(e) => {

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -238,6 +238,7 @@ impl<'a> State<'a> {
                 self.bclose(item.span, empty);
             }
             ast::ItemKind::GlobalAsm(asm) => {
+                // FIXME: Print `builtin # global_asm` once macro `global_asm` uses `builtin_syntax`.
                 self.head(visibility_qualified(&item.vis, "global_asm!"));
                 self.print_inline_asm(asm);
                 self.word(";");

compiler/rustc_expand/src/base.rs

@@ -21,7 +21,7 @@ use rustc_session::config::CollapseMacroDebuginfo;
 use rustc_session::{parse::ParseSess, Limit, Session};
 use rustc_span::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId};
+use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId, MacroKind};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{FileName, Span, DUMMY_SP};
@@ -32,8 +32,6 @@ use std::path::{Path, PathBuf};
 use std::rc::Rc;
 use thin_vec::ThinVec;
 
-pub(crate) use rustc_span::hygiene::MacroKind;
-
 // When adding new variants, make sure to
 // adjust the `visit_*` / `flat_map_*` calls in `InvocationCollector`
 // to use `assign_id!`
@@ -573,35 +571,6 @@ impl DummyResult {
             tokens: None,
         })
     }
-
-    /// A plain dummy pattern.
-    pub fn raw_pat(sp: Span) -> ast::Pat {
-        ast::Pat { id: ast::DUMMY_NODE_ID, kind: PatKind::Wild, span: sp, tokens: None }
-    }
-
-    /// A plain dummy type.
-    pub fn raw_ty(sp: Span) -> P<ast::Ty> {
-        // FIXME(nnethercote): you might expect `ast::TyKind::Dummy` to be used here, but some
-        // values produced here end up being lowered to HIR, which `ast::TyKind::Dummy` does not
-        // support, so we use an empty tuple instead.
-        P(ast::Ty {
-            id: ast::DUMMY_NODE_ID,
-            kind: ast::TyKind::Tup(ThinVec::new()),
-            span: sp,
-            tokens: None,
-        })
-    }
-
-    /// A plain dummy crate.
-    pub fn raw_crate() -> ast::Crate {
-        ast::Crate {
-            attrs: Default::default(),
-            items: Default::default(),
-            spans: Default::default(),
-            id: ast::DUMMY_NODE_ID,
-            is_placeholder: Default::default(),
-        }
-    }
 }
 
 impl MacResult for DummyResult {
@@ -610,7 +579,12 @@ impl MacResult for DummyResult {
     }
 
     fn make_pat(self: Box<DummyResult>) -> Option<P<ast::Pat>> {
-        Some(P(DummyResult::raw_pat(self.span)))
+        Some(P(ast::Pat {
+            id: ast::DUMMY_NODE_ID,
+            kind: PatKind::Wild,
+            span: self.span,
+            tokens: None,
+        }))
     }
 
     fn make_items(self: Box<DummyResult>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
@@ -638,7 +612,15 @@ impl MacResult for DummyResult {
     }
 
     fn make_ty(self: Box<DummyResult>) -> Option<P<ast::Ty>> {
-        Some(DummyResult::raw_ty(self.span))
+        // FIXME(nnethercote): you might expect `ast::TyKind::Dummy` to be used here, but some
+        // values produced here end up being lowered to HIR, which `ast::TyKind::Dummy` does not
+        // support, so we use an empty tuple instead.
+        Some(P(ast::Ty {
+            id: ast::DUMMY_NODE_ID,
+            kind: ast::TyKind::Tup(ThinVec::new()),
+            span: self.span,
+            tokens: None,
+        }))
     }
 
     fn make_arms(self: Box<DummyResult>) -> Option<SmallVec<[ast::Arm; 1]>> {
@@ -670,7 +652,13 @@ impl MacResult for DummyResult {
     }
 
     fn make_crate(self: Box<DummyResult>) -> Option<ast::Crate> {
-        Some(DummyResult::raw_crate())
+        Some(ast::Crate {
+            attrs: Default::default(),
+            items: Default::default(),
+            spans: Default::default(),
+            id: ast::DUMMY_NODE_ID,
+            is_placeholder: Default::default(),
+        })
     }
 }
 

compiler/rustc_expand/src/build.rs

@@ -175,20 +175,6 @@ impl<'a> ExtCtxt<'a> {
         ast::Stmt { id: ast::DUMMY_NODE_ID, span: expr.span, kind: ast::StmtKind::Expr(expr) }
     }
 
-    pub fn stmt_let_pat(&self, sp: Span, pat: P<ast::Pat>, ex: P<ast::Expr>) -> ast::Stmt {
-        let local = P(ast::Local {
-            pat,
-            ty: None,
-            id: ast::DUMMY_NODE_ID,
-            kind: LocalKind::Init(ex),
-            span: sp,
-            colon_sp: None,
-            attrs: AttrVec::new(),
-            tokens: None,
-        });
-        self.stmt_local(local, sp)
-    }
-
     pub fn stmt_let(&self, sp: Span, mutbl: bool, ident: Ident, ex: P<ast::Expr>) -> ast::Stmt {
         self.stmt_let_ty(sp, mutbl, ident, None, ex)
     }
@@ -278,10 +264,6 @@ impl<'a> ExtCtxt<'a> {
         self.expr_ident(span, Ident::with_dummy_span(kw::SelfLower))
     }
 
-    pub fn expr_field(&self, span: Span, expr: P<Expr>, field: Ident) -> P<ast::Expr> {
-        self.expr(span, ast::ExprKind::Field(expr, field))
-    }
-
     pub fn expr_macro_call(&self, span: Span, call: P<ast::MacCall>) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::MacCall(call))
     }
@@ -394,11 +376,6 @@ impl<'a> ExtCtxt<'a> {
         self.expr(span, ast::ExprKind::Lit(lit))
     }
 
-    pub fn expr_char(&self, span: Span, ch: char) -> P<ast::Expr> {
-        let lit = token::Lit::new(token::Char, literal::escape_char_symbol(ch), None);
-        self.expr(span, ast::ExprKind::Lit(lit))
-    }
-
     pub fn expr_byte_str(&self, span: Span, bytes: Vec<u8>) -> P<ast::Expr> {
         let lit = token::Lit::new(token::ByteStr, literal::escape_byte_str_symbol(&bytes), None);
         self.expr(span, ast::ExprKind::Lit(lit))
@@ -414,10 +391,6 @@ impl<'a> ExtCtxt<'a> {
         self.expr_addr_of(sp, self.expr_array(sp, exprs))
     }
 
-    pub fn expr_cast(&self, sp: Span, expr: P<ast::Expr>, ty: P<ast::Ty>) -> P<ast::Expr> {
-        self.expr(sp, ast::ExprKind::Cast(expr, ty))
-    }
-
     pub fn expr_some(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
         let some = self.std_path(&[sym::option, sym::Option, sym::Some]);
         self.expr_call_global(sp, some, thin_vec![expr])

compiler/rustc_expand/src/config.rs

@@ -99,10 +99,11 @@ pub fn features(sess: &Session, krate_attrs: &[Attribute], crate_name: Symbol) -
             // If the declared feature is unstable, record it.
             if let Some(f) = UNSTABLE_FEATURES.iter().find(|f| name == f.feature.name) {
                 (f.set_enabled)(&mut features);
-                // When the ICE comes from core, alloc or std (approximation of the standard library), there's a chance
-                // that the person hitting the ICE may be using -Zbuild-std or similar with an untested target.
-                // The bug is probably in the standard library and not the compiler in that case, but that doesn't
-                // really matter - we want a bug report.
+                // When the ICE comes from core, alloc or std (approximation of the standard
+                // library), there's a chance that the person hitting the ICE may be using
+                // -Zbuild-std or similar with an untested target. The bug is probably in the
+                // standard library and not the compiler in that case, but that doesn't really
+                // matter - we want a bug report.
                 if features.internal(name)
                     && ![sym::core, sym::alloc, sym::std].contains(&crate_name)
                 {

compiler/rustc_expand/src/expand.rs

@@ -4,7 +4,6 @@ use crate::errors::{
     IncompleteParse, RecursionLimitReached, RemoveExprNotSupported, RemoveNodeNotSupported,
     UnsupportedKeyValue, WrongFragmentKind,
 };
-use crate::hygiene::SyntaxContext;
 use crate::mbe::diagnostics::annotate_err_with_kind;
 use crate::module::{mod_dir_path, parse_external_mod, DirOwnership, ParsedExternalMod};
 use crate::placeholders::{placeholder, PlaceholderExpander};
@@ -32,6 +31,7 @@ use rustc_session::lint::builtin::{UNUSED_ATTRIBUTES, UNUSED_DOC_COMMENTS};
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::parse::feature_err;
 use rustc_session::{Limit, Session};
+use rustc_span::hygiene::SyntaxContext;
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::{ErrorGuaranteed, FileName, LocalExpnId, Span};
 
@@ -87,7 +87,7 @@ macro_rules! ast_fragments {
         }
 
         impl AstFragment {
-            pub fn add_placeholders(&mut self, placeholders: &[NodeId]) {
+            fn add_placeholders(&mut self, placeholders: &[NodeId]) {
                 if placeholders.is_empty() {
                     return;
                 }
@@ -100,14 +100,14 @@ macro_rules! ast_fragments {
                 }
             }
 
-            pub fn make_opt_expr(self) -> Option<P<ast::Expr>> {
+            pub(crate) fn make_opt_expr(self) -> Option<P<ast::Expr>> {
                 match self {
                     AstFragment::OptExpr(expr) => expr,
                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
                 }
             }
 
-            pub fn make_method_receiver_expr(self) -> P<ast::Expr> {
+            pub(crate) fn make_method_receiver_expr(self) -> P<ast::Expr> {
                 match self {
                     AstFragment::MethodReceiverExpr(expr) => expr,
                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
@@ -125,7 +125,7 @@ macro_rules! ast_fragments {
                 T::fragment_to_output(self)
             }
 
-            pub fn mut_visit_with<F: MutVisitor>(&mut self, vis: &mut F) {
+            pub(crate) fn mut_visit_with<F: MutVisitor>(&mut self, vis: &mut F) {
                 match self {
                     AstFragment::OptExpr(opt_expr) => {
                         visit_clobber(opt_expr, |opt_expr| {
@@ -372,6 +372,14 @@ impl Invocation {
             InvocationKind::Derive { path, .. } => path.span,
         }
     }
+
+    fn span_mut(&mut self) -> &mut Span {
+        match &mut self.kind {
+            InvocationKind::Bang { span, .. } => span,
+            InvocationKind::Attr { attr, .. } => &mut attr.span,
+            InvocationKind::Derive { path, .. } => &mut path.span,
+        }
+    }
 }
 
 pub struct MacroExpander<'a, 'b> {
@@ -432,7 +440,8 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     break;
                 }
                 invocations = mem::take(&mut undetermined_invocations);
-                force = !mem::replace(&mut progress, false);
+                force = !progress;
+                progress = false;
                 if force && self.monotonic {
                     self.cx.dcx().span_delayed_bug(
                         invocations.last().unwrap().0.span(),
@@ -471,7 +480,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             self.cx.force_mode = force;
 
             let fragment_kind = invoc.fragment_kind;
-            let (expanded_fragment, new_invocations) = match self.expand_invoc(invoc, &ext.kind) {
+            match self.expand_invoc(invoc, &ext.kind) {
                 ExpandResult::Ready(fragment) => {
                     let mut derive_invocations = Vec::new();
                     let derive_placeholders = self
@@ -503,12 +512,19 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         })
                         .unwrap_or_default();
 
-                    let (fragment, collected_invocations) =
+                    let (expanded_fragment, collected_invocations) =
                         self.collect_invocations(fragment, &derive_placeholders);
-                    // We choose to expand any derive invocations associated with this macro invocation
-                    // *before* any macro invocations collected from the output fragment
+                    // We choose to expand any derive invocations associated with this macro
+                    // invocation *before* any macro invocations collected from the output
+                    // fragment.
                     derive_invocations.extend(collected_invocations);
-                    (fragment, derive_invocations)
+
+                    progress = true;
+                    if expanded_fragments.len() < depth {
+                        expanded_fragments.push(Vec::new());
+                    }
+                    expanded_fragments[depth - 1].push((expn_id, expanded_fragment));
+                    invocations.extend(derive_invocations.into_iter().rev());
                 }
                 ExpandResult::Retry(invoc) => {
                     if force {
@@ -519,17 +535,9 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     } else {
                         // Cannot expand, will retry this invocation later.
                         undetermined_invocations.push((invoc, Some(ext)));
-                        continue;
                     }
                 }
-            };
-
-            progress = true;
-            if expanded_fragments.len() < depth {
-                expanded_fragments.push(Vec::new());
             }
-            expanded_fragments[depth - 1].push((expn_id, expanded_fragment));
-            invocations.extend(new_invocations.into_iter().rev());
         }
 
         self.cx.current_expansion = orig_expansion_data;
@@ -590,11 +598,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 for (invoc, _) in invocations.iter_mut() {
                     let expn_id = invoc.expansion_data.id;
                     let parent_def = self.cx.resolver.invocation_parent(expn_id);
-                    let span = match &mut invoc.kind {
-                        InvocationKind::Bang { span, .. } => span,
-                        InvocationKind::Attr { attr, .. } => &mut attr.span,
-                        InvocationKind::Derive { path, .. } => &mut path.span,
-                    };
+                    let span = invoc.span_mut();
                     *span = span.with_parent(Some(parent_def));
                 }
             }
@@ -957,7 +961,7 @@ pub fn parse_ast_fragment<'a>(
     })
 }
 
-pub fn ensure_complete_parse<'a>(
+pub(crate) fn ensure_complete_parse<'a>(
     parser: &Parser<'a>,
     macro_path: &ast::Path,
     kind_name: &str,

compiler/rustc_expand/src/lib.rs

@@ -1,43 +1,39 @@
+// tidy-alphabetical-start
+#![allow(internal_features)]
+#![allow(rustc::diagnostic_outside_of_impl)]
 #![doc(rust_logo)]
-#![feature(rustdoc_internals)]
 #![feature(array_windows)]
 #![feature(associated_type_defaults)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
-#![feature(lint_reasons)]
 #![feature(macro_metavar_expr)]
 #![feature(map_try_insert)]
 #![feature(proc_macro_diagnostic)]
 #![feature(proc_macro_internals)]
-#![feature(proc_macro_span)]
+#![feature(rustdoc_internals)]
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
-#![allow(rustc::diagnostic_outside_of_impl)]
-#![allow(internal_features)]
+// tidy-alphabetical-end
 
 extern crate proc_macro as pm;
 
+mod build;
+mod errors;
+// FIXME(Nilstrieb) Translate macro_rules diagnostics
+#[allow(rustc::untranslatable_diagnostic)]
+mod mbe;
 mod placeholders;
 mod proc_macro_server;
 
 pub use mbe::macro_rules::compile_declarative_macro;
-pub(crate) use rustc_span::hygiene;
 pub mod base;
-pub mod build;
-#[macro_use]
 pub mod config;
-pub mod errors;
 pub mod expand;
 pub mod module;
-
 // FIXME(Nilstrieb) Translate proc_macro diagnostics
 #[allow(rustc::untranslatable_diagnostic)]
 pub mod proc_macro;
 
-// FIXME(Nilstrieb) Translate macro_rules diagnostics
-#[allow(rustc::untranslatable_diagnostic)]
-pub(crate) mod mbe;
-
 // HACK(Centril, #64197): These shouldn't really be here.
 // Rather, they should be with their respective modules which are defined in other crates.
 // However, since for now constructing a `ParseSess` sorta requires `config` from this crate,

compiler/rustc_expand/src/mbe.rs

@@ -4,12 +4,13 @@
 //! official terminology: "declarative macros".
 
 pub(crate) mod diagnostics;
-pub(crate) mod macro_check;
-pub(crate) mod macro_parser;
 pub(crate) mod macro_rules;
-pub(crate) mod metavar_expr;
-pub(crate) mod quoted;
-pub(crate) mod transcribe;
+
+mod macro_check;
+mod macro_parser;
+mod metavar_expr;
+mod quoted;
+mod transcribe;
 
 use metavar_expr::MetaVarExpr;
 use rustc_ast::token::{Delimiter, NonterminalKind, Token, TokenKind};

compiler/rustc_expand/src/mbe/diagnostics.rs

@@ -28,7 +28,8 @@ pub(super) fn failed_to_match_macro<'cx>(
 ) -> Box<dyn MacResult + 'cx> {
     let psess = &cx.sess.psess;
 
-    // An error occurred, try the expansion again, tracking the expansion closely for better diagnostics.
+    // An error occurred, try the expansion again, tracking the expansion closely for better
+    // diagnostics.
     let mut tracker = CollectTrackerAndEmitter::new(cx, sp);
 
     let try_success_result = try_match_macro(psess, name, &arg, lhses, &mut tracker);

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -157,8 +157,8 @@ pub(super) trait Tracker<'matcher> {
     /// This is called before trying to match next MatcherLoc on the current token.
     fn before_match_loc(&mut self, _parser: &TtParser, _matcher: &'matcher MatcherLoc) {}
 
-    /// This is called after an arm has been parsed, either successfully or unsuccessfully. When this is called,
-    /// `before_match_loc` was called at least once (with a `MatcherLoc::Eof`).
+    /// This is called after an arm has been parsed, either successfully or unsuccessfully. When
+    /// this is called, `before_match_loc` was called at least once (with a `MatcherLoc::Eof`).
     fn after_arm(&mut self, _result: &NamedParseResult<Self::Failure>) {}
 
     /// For tracing.
@@ -169,7 +169,8 @@ pub(super) trait Tracker<'matcher> {
     }
 }
 
-/// A noop tracker that is used in the hot path of the expansion, has zero overhead thanks to monomorphization.
+/// A noop tracker that is used in the hot path of the expansion, has zero overhead thanks to
+/// monomorphization.
 pub(super) struct NoopTracker;
 
 impl<'matcher> Tracker<'matcher> for NoopTracker {
@@ -492,7 +493,7 @@ pub fn compile_declarative_macro(
                     .pop()
                     .unwrap();
                     // We don't handle errors here, the driver will abort
-                    // after parsing/expansion. we can report every error in every macro this way.
+                    // after parsing/expansion. We can report every error in every macro this way.
                     check_emission(check_lhs_nt_follows(sess, def, &tt));
                     return tt;
                 }
@@ -528,7 +529,7 @@ pub fn compile_declarative_macro(
         check_emission(check_rhs(sess, rhs));
     }
 
-    // don't abort iteration early, so that errors for multiple lhses can be reported
+    // Don't abort iteration early, so that errors for multiple lhses can be reported.
     for lhs in &lhses {
         check_emission(check_lhs_no_empty_seq(sess, slice::from_ref(lhs)));
     }

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -39,40 +39,42 @@ impl MutVisitor for Marker {
 }
 
 /// An iterator over the token trees in a delimited token tree (`{ ... }`) or a sequence (`$(...)`).
-enum Frame<'a> {
-    Delimited {
-        tts: &'a [mbe::TokenTree],
-        idx: usize,
-        delim: Delimiter,
-        span: DelimSpan,
-        spacing: DelimSpacing,
-    },
-    Sequence {
-        tts: &'a [mbe::TokenTree],
-        idx: usize,
-        sep: Option<Token>,
-        kleene_op: KleeneOp,
-    },
+struct Frame<'a> {
+    tts: &'a [mbe::TokenTree],
+    idx: usize,
+    kind: FrameKind,
+}
+
+enum FrameKind {
+    Delimited { delim: Delimiter, span: DelimSpan, spacing: DelimSpacing },
+    Sequence { sep: Option<Token>, kleene_op: KleeneOp },
 }
 
 impl<'a> Frame<'a> {
-    /// Construct a new frame around the delimited set of tokens.
-    fn new(src: &'a mbe::Delimited, span: DelimSpan, spacing: DelimSpacing) -> Frame<'a> {
-        Frame::Delimited { tts: &src.tts, idx: 0, delim: src.delim, span, spacing }
+    fn new_delimited(src: &'a mbe::Delimited, span: DelimSpan, spacing: DelimSpacing) -> Frame<'a> {
+        Frame {
+            tts: &src.tts,
+            idx: 0,
+            kind: FrameKind::Delimited { delim: src.delim, span, spacing },
+        }
+    }
+
+    fn new_sequence(
+        src: &'a mbe::SequenceRepetition,
+        sep: Option<Token>,
+        kleene_op: KleeneOp,
+    ) -> Frame<'a> {
+        Frame { tts: &src.tts, idx: 0, kind: FrameKind::Sequence { sep, kleene_op } }
     }
 }
 
 impl<'a> Iterator for Frame<'a> {
     type Item = &'a mbe::TokenTree;
 
     fn next(&mut self) -> Option<&'a mbe::TokenTree> {
-        match self {
-            Frame::Delimited { tts, idx, .. } | Frame::Sequence { tts, idx, .. } => {
-                let res = tts.get(*idx);
-                *idx += 1;
-                res
-            }
-        }
+        let res = self.tts.get(self.idx);
+        self.idx += 1;
+        res
     }
 }
 
@@ -111,13 +113,16 @@ pub(super) fn transcribe<'a>(
     // We descend into the RHS (`src`), expanding things as we go. This stack contains the things
     // we have yet to expand/are still expanding. We start the stack off with the whole RHS. The
     // choice of spacing values doesn't matter.
-    let mut stack: SmallVec<[Frame<'_>; 1]> =
-        smallvec![Frame::new(src, src_span, DelimSpacing::new(Spacing::Alone, Spacing::Alone))];
+    let mut stack: SmallVec<[Frame<'_>; 1]> = smallvec![Frame::new_delimited(
+        src,
+        src_span,
+        DelimSpacing::new(Spacing::Alone, Spacing::Alone)
+    )];
 
     // As we descend in the RHS, we will need to be able to match nested sequences of matchers.
     // `repeats` keeps track of where we are in matching at each level, with the last element being
     // the most deeply nested sequence. This is used as a stack.
-    let mut repeats = Vec::new();
+    let mut repeats: Vec<(usize, usize)> = Vec::new();
 
     // `result` contains resulting token stream from the TokenTree we just finished processing. At
     // the end, this will contain the full result of transcription, but at arbitrary points during
@@ -142,11 +147,12 @@ pub(super) fn transcribe<'a>(
 
             // Otherwise, if we have just reached the end of a sequence and we can keep repeating,
             // go back to the beginning of the sequence.
-            if let Frame::Sequence { idx, sep, .. } = stack.last_mut().unwrap() {
+            let frame = stack.last_mut().unwrap();
+            if let FrameKind::Sequence { sep, .. } = &frame.kind {
                 let (repeat_idx, repeat_len) = repeats.last_mut().unwrap();
                 *repeat_idx += 1;
                 if repeat_idx < repeat_len {
-                    *idx = 0;
+                    frame.idx = 0;
                     if let Some(sep) = sep {
                         result.push(TokenTree::Token(sep.clone(), Spacing::Alone));
                     }
@@ -157,16 +163,16 @@ pub(super) fn transcribe<'a>(
             // We are done with the top of the stack. Pop it. Depending on what it was, we do
             // different things. Note that the outermost item must be the delimited, wrapped RHS
             // that was passed in originally to `transcribe`.
-            match stack.pop().unwrap() {
+            match stack.pop().unwrap().kind {
                 // Done with a sequence. Pop from repeats.
-                Frame::Sequence { .. } => {
+                FrameKind::Sequence { .. } => {
                     repeats.pop();
                 }
 
                 // We are done processing a Delimited. If this is the top-level delimited, we are
                 // done. Otherwise, we unwind the result_stack to append what we have produced to
                 // any previous results.
-                Frame::Delimited { delim, span, mut spacing, .. } => {
+                FrameKind::Delimited { delim, span, mut spacing, .. } => {
                     // Hack to force-insert a space after `]` in certain case.
                     // See discussion of the `hex-literal` crate in #114571.
                     if delim == Delimiter::Bracket {
@@ -192,7 +198,7 @@ pub(super) fn transcribe<'a>(
             // We are descending into a sequence. We first make sure that the matchers in the RHS
             // and the matches in `interp` have the same shape. Otherwise, either the caller or the
             // macro writer has made a mistake.
-            seq @ mbe::TokenTree::Sequence(_, delimited) => {
+            seq @ mbe::TokenTree::Sequence(_, seq_rep) => {
                 match lockstep_iter_size(seq, interp, &repeats) {
                     LockstepIterSize::Unconstrained => {
                         return Err(cx
@@ -233,12 +239,11 @@ pub(super) fn transcribe<'a>(
                             // The first time we encounter the sequence we push it to the stack. It
                             // then gets reused (see the beginning of the loop) until we are done
                             // repeating.
-                            stack.push(Frame::Sequence {
-                                idx: 0,
-                                sep: seq.separator.clone(),
-                                tts: &delimited.tts,
-                                kleene_op: seq.kleene.op,
-                            });
+                            stack.push(Frame::new_sequence(
+                                seq_rep,
+                                seq.separator.clone(),
+                                seq.kleene.op,
+                            ));
                         }
                     }
                 }
@@ -294,13 +299,7 @@ pub(super) fn transcribe<'a>(
             // the previous results (from outside the Delimited).
             mbe::TokenTree::Delimited(mut span, spacing, delimited) => {
                 mut_visit::visit_delim_span(&mut span, &mut marker);
-                stack.push(Frame::Delimited {
-                    tts: &delimited.tts,
-                    delim: delimited.delim,
-                    idx: 0,
-                    span,
-                    spacing: *spacing,
-                });
+                stack.push(Frame::new_delimited(delimited, span, *spacing));
                 result_stack.push(mem::take(&mut result));
             }
 
@@ -358,10 +357,13 @@ fn maybe_use_metavar_location(
 ) -> TokenTree {
     let undelimited_seq = matches!(
         stack.last(),
-        Some(Frame::Sequence {
+        Some(Frame {
             tts: [_],
-            sep: None,
-            kleene_op: KleeneOp::ZeroOrMore | KleeneOp::OneOrMore,
+            kind: FrameKind::Sequence {
+                sep: None,
+                kleene_op: KleeneOp::ZeroOrMore | KleeneOp::OneOrMore,
+                ..
+            },
             ..
         })
     );

compiler/rustc_expand/src/placeholders.rs

@@ -9,7 +9,7 @@ use rustc_span::DUMMY_SP;
 use smallvec::{smallvec, SmallVec};
 use thin_vec::ThinVec;
 
-pub fn placeholder(
+pub(crate) fn placeholder(
     kind: AstFragmentKind,
     id: ast::NodeId,
     vis: Option<ast::Visibility>,

compiler/rustc_middle/src/ty/fast_reject.rs

@@ -330,20 +330,19 @@ impl DeepRejectCtxt {
     }
 
     pub fn consts_may_unify(self, obligation_ct: ty::Const<'_>, impl_ct: ty::Const<'_>) -> bool {
-        match impl_ct.kind() {
+        let impl_val = match impl_ct.kind() {
             ty::ConstKind::Expr(_)
             | ty::ConstKind::Param(_)
             | ty::ConstKind::Unevaluated(_)
             | ty::ConstKind::Error(_) => {
                 return true;
             }
-            ty::ConstKind::Value(_) => {}
+            ty::ConstKind::Value(impl_val) => impl_val,
             ty::ConstKind::Infer(_) | ty::ConstKind::Bound(..) | ty::ConstKind::Placeholder(_) => {
                 bug!("unexpected impl arg: {:?}", impl_ct)
             }
-        }
+        };
 
-        let k = impl_ct.kind();
         match obligation_ct.kind() {
             ty::ConstKind::Param(_) => match self.treat_obligation_params {
                 TreatParams::ForLookup => false,
@@ -358,10 +357,7 @@ impl DeepRejectCtxt {
             ty::ConstKind::Expr(_) | ty::ConstKind::Unevaluated(_) | ty::ConstKind::Error(_) => {
                 true
             }
-            ty::ConstKind::Value(obl) => match k {
-                ty::ConstKind::Value(imp) => obl == imp,
-                _ => true,
-            },
+            ty::ConstKind::Value(obl_val) => obl_val == impl_val,
 
             ty::ConstKind::Infer(_) => true,
 

library/alloc/src/borrow.rs

@@ -4,9 +4,9 @@
 
 use core::cmp::Ordering;
 use core::hash::{Hash, Hasher};
-use core::ops::Deref;
 #[cfg(not(no_global_oom_handling))]
 use core::ops::{Add, AddAssign};
+use core::ops::{Deref, DerefPure};
 
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::borrow::{Borrow, BorrowMut};
@@ -343,6 +343,9 @@ where
     }
 }
 
+#[unstable(feature = "deref_pure_trait", issue = "87121")]
+unsafe impl<B: ?Sized + ToOwned> DerefPure for Cow<'_, B> where B::Owned: Borrow<B> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<B: ?Sized> Eq for Cow<'_, B> where B: Eq + ToOwned {}
 

library/alloc/src/string.rs

@@ -1382,7 +1382,7 @@ impl String {
 
     /// Shortens this `String` to the specified length.
     ///
-    /// If `new_len` is greater than the string's current length, this has no
+    /// If `new_len` is greater than or equal to the string's current length, this has no
     /// effect.
     ///
     /// Note that this method has no effect on the allocated capacity

library/core/src/cell.rs

@@ -239,7 +239,7 @@ use crate::cmp::Ordering;
 use crate::fmt::{self, Debug, Display};
 use crate::marker::{PhantomData, Unsize};
 use crate::mem::{self, size_of};
-use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn};
+use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn};
 use crate::ptr::{self, NonNull};
 
 mod lazy;
@@ -1452,6 +1452,9 @@ impl<T: ?Sized> Deref for Ref<'_, T> {
     }
 }
 
+#[unstable(feature = "deref_pure_trait", issue = "87121")]
+unsafe impl<T: ?Sized> DerefPure for Ref<'_, T> {}
+
 impl<'b, T: ?Sized> Ref<'b, T> {
     /// Copies a `Ref`.
     ///
@@ -1844,6 +1847,9 @@ impl<T: ?Sized> DerefMut for RefMut<'_, T> {
     }
 }
 
+#[unstable(feature = "deref_pure_trait", issue = "87121")]
+unsafe impl<T: ?Sized> DerefPure for RefMut<'_, T> {}
+
 #[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<'b, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<RefMut<'b, U>> for RefMut<'b, T> {}
 

library/core/src/intrinsics.rs

@@ -2578,8 +2578,7 @@ extern "rust-intrinsic" {
 ///
 /// Currently such an assertion would always succeed; until Rust decides
 /// otherwise, that principle should not be violated.
-#[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
-#[unstable(feature = "core_intrinsics", issue = "none")]
+#[rustc_const_unstable(feature = "const_eval_select", issue = "124625")]
 #[rustc_intrinsic]
 #[rustc_intrinsic_must_be_overridden]
 pub const fn const_eval_select<ARG: Tuple, F, G, RET>(

library/core/src/mem/manually_drop.rs

@@ -1,4 +1,4 @@
-use crate::ops::{Deref, DerefMut};
+use crate::ops::{Deref, DerefMut, DerefPure};
 use crate::ptr;
 
 /// A wrapper to inhibit compiler from automatically calling `T`’s destructor.
@@ -161,3 +161,6 @@ impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
         &mut self.value
     }
 }
+
+#[unstable(feature = "deref_pure_trait", issue = "87121")]
+unsafe impl<T: ?Sized> DerefPure for ManuallyDrop<T> {}

library/core/src/pin.rs

@@ -923,7 +923,7 @@
 use crate::cmp;
 use crate::fmt;
 use crate::hash::{Hash, Hasher};
-use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn, Receiver};
+use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, Receiver};
 
 #[allow(unused_imports)]
 use crate::{
@@ -1684,6 +1684,9 @@ impl<Ptr: DerefMut<Target: Unpin>> DerefMut for Pin<Ptr> {
     }
 }
 
+#[unstable(feature = "deref_pure_trait", issue = "87121")]
+unsafe impl<Ptr: DerefPure> DerefPure for Pin<Ptr> {}
+
 #[unstable(feature = "receiver_trait", issue = "none")]
 impl<Ptr: Receiver> Receiver for Pin<Ptr> {}
 

library/std/Cargo.toml

@@ -64,12 +64,10 @@ r-efi-alloc = { version = "1.0.0", features = ['rustc-dep-of-std'] }
 
 [features]
 backtrace = [
-  "gimli-symbolize",
   'addr2line/rustc-dep-of-std',
   'object/rustc-dep-of-std',
   'miniz_oxide/rustc-dep-of-std',
 ]
-gimli-symbolize = []
 
 panic-unwind = ["panic_unwind"]
 profiler = ["profiler_builtins"]

library/std/src/f32.rs

@@ -266,7 +266,7 @@
 //! its file descriptors with no operations being performed by any other part of the program.
 //!
 //! Note that exclusive ownership of a file descriptor does *not* imply exclusive ownership of the
-//! underlying kernel object that the file descriptor references (also called "file description" on
+//! underlying kernel object that the file descriptor references (also called "open file description" on
 //! some operating systems). File descriptors basically work like [`Arc`]: when you receive an owned
 //! file descriptor, you cannot know whether there are any other file descriptors that reference the
 //! same kernel object. However, when you create a new kernel object, you know that you are holding

library/std/src/f64.rs

@@ -12,8 +12,8 @@
 //! | Type               | Analogous to |
 //! | ------------------ | ------------ |
 //! | [`RawFd`]          | `*const _`   |
-//! | [`BorrowedFd<'a>`] | `&'a _`      |
-//! | [`OwnedFd`]        | `Box<_>`     |
+//! | [`BorrowedFd<'a>`] | `&'a Arc<_>` |
+//! | [`OwnedFd`]        | `Arc<_>`     |
 //!
 //! Like raw pointers, `RawFd` values are primitive values. And in new code,
 //! they should be considered unsafe to do I/O on (analogous to dereferencing
@@ -23,22 +23,31 @@
 //! either by adding `unsafe` to APIs that dereference `RawFd` values, or by
 //! using to `BorrowedFd` or `OwnedFd` instead.
 //!
+//! The use of `Arc` for borrowed/owned file descriptors may be surprising. Unix file descriptors
+//! are mere references to internal kernel objects called "open file descriptions", and the same
+//! open file description can be referenced by multiple file descriptors (e.g. if `dup` is used).
+//! State such as the offset within the file is shared among all file descriptors that refer to the
+//! same open file description, and the kernel internally does reference-counting to only close the
+//! underlying resource once all file descriptors referencing it are closed. That's why `Arc` (and
+//! not `Box`) is the closest Rust analogy to an "owned" file descriptor.
+//!
 //! Like references, `BorrowedFd` values are tied to a lifetime, to ensure
 //! that they don't outlive the resource they point to. These are safe to
 //! use. `BorrowedFd` values may be used in APIs which provide safe access to
 //! any system call except for:
 //!
 //!  - `close`, because that would end the dynamic lifetime of the resource
-//!    without ending the lifetime of the file descriptor.
+//!    without ending the lifetime of the file descriptor. (Equivalently:
+//!    an `&Arc<_>` cannot be `drop`ed.)
 //!
 //!  - `dup2`/`dup3`, in the second argument, because this argument is
-//!    closed and assigned a new resource, which may break the assumptions
+//!    closed and assigned a new resource, which may break the assumptions of
 //!    other code using that file descriptor.
 //!
-//! `BorrowedFd` values may be used in APIs which provide safe access to `dup`
-//! system calls, so types implementing `AsFd` or `From<OwnedFd>` should not
-//! assume they always have exclusive access to the underlying file
-//! description.
+//! `BorrowedFd` values may be used in APIs which provide safe access to `dup` system calls, so code
+//! working with `OwnedFd` cannot assume to have exclusive access to the underlying open file
+//! description. (Equivalently: `&Arc` may be used in APIs that provide safe access to `clone`, so
+//! code working with an `Arc` cannot assume that the reference count is 1.)
 //!
 //! `BorrowedFd` values may also be used with `mmap`, since `mmap` uses the
 //! provided file descriptor in a manner similar to `dup` and does not require
@@ -52,8 +61,10 @@
 //! take full responsibility for ensuring that safe Rust code cannot evoke
 //! undefined behavior through it.
 //!
-//! Like boxes, `OwnedFd` values conceptually own the resource they point to,
-//! and free (close) it when they are dropped.
+//! Like `Arc`, `OwnedFd` values conceptually own one reference to the resource they point to,
+//! and decrement the reference count when they are dropped (by calling `close`).
+//! When the reference count reaches 0, the underlying open file description will be freed
+//! by the kernel.
 //!
 //! See the [`io` module docs][io-safety] for a general explanation of I/O safety.
 //!

library/std/src/io/mod.rs

@@ -161,8 +161,9 @@ pub fn extra_cxx_flags() -> Vec<&'static str> {
     if is_windows() {
         if is_msvc() { vec![] } else { vec!["-lstdc++"] }
     } else {
-        match uname() {
-            n if n.contains("Darwin") => vec!["-lc++"],
+        match &uname()[..] {
+            "Darwin" => vec!["-lc++"],
+            "FreeBSD" | "SunOS" | "OpenBSD" => vec![],
             _ => vec!["-lstdc++"],
         }
     }