Auto merge of #130674 - compiler-errors:rollup-yu105fl, r=compiler-errors

Rollup of 8 pull requests

Successful merges:

 - #127766 (add `extern "C-cmse-nonsecure-entry" fn` )
 - #129629 (Implement Return Type Notation (RTN)'s path form in where clauses)
 - #130408 (Avoid re-validating UTF-8 in `FromUtf8Error::into_utf8_lossy`)
 - #130651 (Add --enable-profiler to armhf dist)
 - #130653 (ABI compatibility: mention Result guarantee)
 - #130666 (Assert that `explicit_super_predicates_of` and `explicit_item_super_predicates` truly only contains bounds for the type itself)
 - #130667 (compiler: Accept "improper" ctypes in extern "rust-cold" fn)
 - #130673 (Parser: recover from `:::` to `::`)

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

6 files changed, 110 insertions, 17 deletions

diff --git a/compiler/rustc_ast_lowering/src/asm.rs b/compiler/rustc_ast_lowering/src/asm.rs
index a9d1ee5c9c1..6c966c9f73a 100644
--- a/compiler/rustc_ast_lowering/src/asm.rs
+++ b/compiler/rustc_ast_lowering/src/asm.rs
@@ -20,8 +20,8 @@ use super::errors::{
 };
 use super::LoweringContext;
 use crate::{
-    fluent_generated as fluent, ImplTraitContext, ImplTraitPosition, ParamMode,
-    ResolverAstLoweringExt,
+    fluent_generated as fluent, AllowReturnTypeNotation, ImplTraitContext, ImplTraitPosition,
+    ParamMode, ResolverAstLoweringExt,
 };
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
@@ -201,6 +201,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                 &sym.qself,
                                 &sym.path,
                                 ParamMode::Optional,
+                                AllowReturnTypeNotation::No,
                                 ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                                 None,
                             );
diff --git a/compiler/rustc_ast_lowering/src/delegation.rs b/compiler/rustc_ast_lowering/src/delegation.rs
index ac527df474a..97483e85f77 100644
--- a/compiler/rustc_ast_lowering/src/delegation.rs
+++ b/compiler/rustc_ast_lowering/src/delegation.rs
@@ -52,7 +52,7 @@ use rustc_target::spec::abi;
 use {rustc_ast as ast, rustc_hir as hir};
 
 use super::{GenericArgsMode, ImplTraitContext, LoweringContext, ParamMode};
-use crate::{ImplTraitPosition, ResolverAstLoweringExt};
+use crate::{AllowReturnTypeNotation, ImplTraitPosition, ResolverAstLoweringExt};
 
 pub(crate) struct DelegationResults<'hir> {
     pub body_id: hir::BodyId,
@@ -340,6 +340,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 &delegation.qself,
                 &delegation.path,
                 ParamMode::Optional,
+                AllowReturnTypeNotation::No,
                 ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                 None,
             );
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index e105026ebd1..974144cc8d9 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -23,7 +23,7 @@ use super::{
     GenericArgsMode, ImplTraitContext, LoweringContext, ParamMode, ResolverAstLoweringExt,
 };
 use crate::errors::YieldInClosure;
-use crate::{fluent_generated, FnDeclKind, ImplTraitPosition};
+use crate::{fluent_generated, AllowReturnTypeNotation, FnDeclKind, ImplTraitPosition};
 
 impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
@@ -281,6 +281,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         qself,
                         path,
                         ParamMode::Optional,
+                        AllowReturnTypeNotation::No,
                         ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                         None,
                     );
@@ -328,6 +329,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             &se.qself,
                             &se.path,
                             ParamMode::Optional,
+                            AllowReturnTypeNotation::No,
                             ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                             None,
                         )),
@@ -1291,6 +1293,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         qself,
                         path,
                         ParamMode::Optional,
+                        AllowReturnTypeNotation::No,
                         ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                         None,
                     );
@@ -1311,6 +1314,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         qself,
                         path,
                         ParamMode::Optional,
+                        AllowReturnTypeNotation::No,
                         ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                         None,
                     );
@@ -1336,6 +1340,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     &se.qself,
                     &se.path,
                     ParamMode::Optional,
+                    AllowReturnTypeNotation::No,
                     ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                     None,
                 );
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index efd3ae336af..d13e26d2510 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -485,9 +485,23 @@ enum ParamMode {
     Optional,
 }
 
+#[derive(Copy, Clone, Debug)]
+enum AllowReturnTypeNotation {
+    /// Only in types, since RTN is denied later during HIR lowering.
+    Yes,
+    /// All other positions (path expr, method, use tree).
+    No,
+}
+
 enum GenericArgsMode {
+    /// Allow paren sugar, don't allow RTN.
     ParenSugar,
+    /// Allow RTN, don't allow paren sugar.
+    ReturnTypeNotation,
+    // Error if parenthesized generics or RTN are encountered.
     Err,
+    /// Silence errors when lowering generics. Only used with `Res::Err`.
+    Silence,
 }
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
@@ -1226,7 +1240,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         }
 
         let id = self.lower_node_id(t.id);
-        let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx, None);
+        let qpath = self.lower_qpath(
+            t.id,
+            qself,
+            path,
+            param_mode,
+            AllowReturnTypeNotation::Yes,
+            itctx,
+            None,
+        );
         self.ty_path(id, t.span, qpath)
     }
 
@@ -2203,6 +2225,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             &None,
             &p.path,
             ParamMode::Explicit,
+            AllowReturnTypeNotation::No,
             itctx,
             Some(modifiers),
         ) {
@@ -2341,6 +2364,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     &None,
                     path,
                     ParamMode::Optional,
+                    AllowReturnTypeNotation::No,
                     ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                     None,
                 );
@@ -2419,6 +2443,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 qself,
                 path,
                 ParamMode::Optional,
+                AllowReturnTypeNotation::No,
                 ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                 None,
             );
diff --git a/compiler/rustc_ast_lowering/src/pat.rs b/compiler/rustc_ast_lowering/src/pat.rs
index d82bdd526b7..584d94ebe2d 100644
--- a/compiler/rustc_ast_lowering/src/pat.rs
+++ b/compiler/rustc_ast_lowering/src/pat.rs
@@ -11,7 +11,7 @@ use super::errors::{
     ArbitraryExpressionInPattern, ExtraDoubleDot, MisplacedDoubleDot, SubTupleBinding,
 };
 use super::{ImplTraitContext, LoweringContext, ParamMode, ResolverAstLoweringExt};
-use crate::ImplTraitPosition;
+use crate::{AllowReturnTypeNotation, ImplTraitPosition};
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
     pub(crate) fn lower_pat(&mut self, pattern: &Pat) -> &'hir hir::Pat<'hir> {
@@ -38,6 +38,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             qself,
                             path,
                             ParamMode::Optional,
+                            AllowReturnTypeNotation::No,
                             ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                             None,
                         );
@@ -55,6 +56,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             qself,
                             path,
                             ParamMode::Optional,
+                            AllowReturnTypeNotation::No,
                             ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                             None,
                         );
@@ -66,6 +68,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             qself,
                             path,
                             ParamMode::Optional,
+                            AllowReturnTypeNotation::No,
                             ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                             None,
                         );
diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs
index 2ab30eff6d8..03c8097e4c3 100644
--- a/compiler/rustc_ast_lowering/src/path.rs
+++ b/compiler/rustc_ast_lowering/src/path.rs
@@ -5,6 +5,7 @@ use rustc_hir::def::{DefKind, PartialRes, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::GenericArg;
 use rustc_middle::span_bug;
+use rustc_session::parse::add_feature_diagnostics;
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, DesugaringKind, Span, Symbol, DUMMY_SP};
 use smallvec::{smallvec, SmallVec};
@@ -15,10 +16,9 @@ use super::errors::{
     GenericTypeWithParentheses, UseAngleBrackets,
 };
 use super::{
-    GenericArgsCtor, GenericArgsMode, ImplTraitContext, LifetimeRes, LoweringContext, ParamMode,
-    ResolverAstLoweringExt,
+    AllowReturnTypeNotation, GenericArgsCtor, GenericArgsMode, ImplTraitContext, ImplTraitPosition,
+    LifetimeRes, LoweringContext, ParamMode, ResolverAstLoweringExt,
 };
-use crate::ImplTraitPosition;
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
     #[instrument(level = "trace", skip(self))]
@@ -28,6 +28,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         qself: &Option<ptr::P<QSelf>>,
         p: &Path,
         param_mode: ParamMode,
+        allow_return_type_notation: AllowReturnTypeNotation,
         itctx: ImplTraitContext,
         // modifiers of the impl/bound if this is a trait path
         modifiers: Option<ast::TraitBoundModifiers>,
@@ -103,8 +104,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         {
                             GenericArgsMode::ParenSugar
                         }
+                        Res::Def(DefKind::AssocFn, _) if i + 1 == proj_start => {
+                            match allow_return_type_notation {
+                                AllowReturnTypeNotation::Yes => GenericArgsMode::ReturnTypeNotation,
+                                AllowReturnTypeNotation::No => GenericArgsMode::Err,
+                            }
+                        }
                         // Avoid duplicated errors.
-                        Res::Err => GenericArgsMode::ParenSugar,
+                        Res::Err => GenericArgsMode::Silence,
                         // An error
                         _ => GenericArgsMode::Err,
                     };
@@ -164,11 +171,20 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
         // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
         for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
+            // If this is a type-dependent `T::method(..)`.
+            let generic_args_mode = if i + 1 == p.segments.len()
+                && matches!(allow_return_type_notation, AllowReturnTypeNotation::Yes)
+            {
+                GenericArgsMode::ReturnTypeNotation
+            } else {
+                GenericArgsMode::Err
+            };
+
             let hir_segment = self.arena.alloc(self.lower_path_segment(
                 p.span,
                 segment,
                 param_mode,
-                GenericArgsMode::Err,
+                generic_args_mode,
                 itctx,
                 None,
             ));
@@ -238,11 +254,46 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
                 }
                 GenericArgs::Parenthesized(data) => match generic_args_mode {
-                    GenericArgsMode::ParenSugar => self.lower_parenthesized_parameter_data(
-                        data,
-                        itctx,
-                        bound_modifier_allowed_features,
-                    ),
+                    GenericArgsMode::ReturnTypeNotation => {
+                        let mut err = if !data.inputs.is_empty() {
+                            self.dcx().create_err(BadReturnTypeNotation::Inputs {
+                                span: data.inputs_span,
+                            })
+                        } else if let FnRetTy::Ty(ty) = &data.output {
+                            self.dcx().create_err(BadReturnTypeNotation::Output {
+                                span: data.inputs_span.shrink_to_hi().to(ty.span),
+                            })
+                        } else {
+                            self.dcx().create_err(BadReturnTypeNotation::NeedsDots {
+                                span: data.inputs_span,
+                            })
+                        };
+                        if !self.tcx.features().return_type_notation
+                            && self.tcx.sess.is_nightly_build()
+                        {
+                            add_feature_diagnostics(
+                                &mut err,
+                                &self.tcx.sess,
+                                sym::return_type_notation,
+                            );
+                        }
+                        err.emit();
+                        (
+                            GenericArgsCtor {
+                                args: Default::default(),
+                                constraints: &[],
+                                parenthesized: hir::GenericArgsParentheses::ReturnTypeNotation,
+                                span: path_span,
+                            },
+                            false,
+                        )
+                    }
+                    GenericArgsMode::ParenSugar | GenericArgsMode::Silence => self
+                        .lower_parenthesized_parameter_data(
+                            data,
+                            itctx,
+                            bound_modifier_allowed_features,
+                        ),
                     GenericArgsMode::Err => {
                         // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
                         let sub = if !data.inputs.is_empty() {
@@ -279,7 +330,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     }
                 },
                 GenericArgs::ParenthesizedElided(span) => {
-                    self.dcx().emit_err(BadReturnTypeNotation::Position { span: *span });
+                    match generic_args_mode {
+                        GenericArgsMode::ReturnTypeNotation | GenericArgsMode::Silence => {
+                            // Ok
+                        }
+                        GenericArgsMode::ParenSugar | GenericArgsMode::Err => {
+                            self.dcx().emit_err(BadReturnTypeNotation::Position { span: *span });
+                        }
+                    }
                     (
                         GenericArgsCtor {
                             args: Default::default(),