Allow attributes in function trait parameters

compiler/rustc_ast_lowering/src/path.rs

@@ -1,10 +1,11 @@
 use std::sync::Arc;
 
 use rustc_ast::{self as ast, *};
+use rustc_attr_ir::target::Target;
 use rustc_errors::StashKey;
 use rustc_hir::def::{DefKind, PerNS, Res};
 use rustc_hir::def_id::DefId;
-use rustc_hir::{self as hir, GenericArg};
+use rustc_hir::{self as hir, GenericArg, HirId};
 use rustc_middle::middle::resolve::PartialRes;
 use rustc_middle::ty;
 use rustc_session::diagnostics::add_feature_diagnostics;
@@ -263,6 +264,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
         bound_modifier_allowed_features: Option<Arc<[Symbol]>>,
     ) -> hir::PathSegment<'hir> {
         debug!("path_span: {:?}, lower_path_segment(segment: {:?})", path_span, segment);
+
+        let res = self.expect_full_res(segment.id);
+        let hir_id = self.lower_node_id(segment.id);
+
         let (mut generic_args, infer_args) = if let Some(generic_args) = segment.args.as_deref() {
             match generic_args {
                 GenericArgs::AngleBracketed(data) => {
@@ -315,6 +320,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             data,
                             itctx,
                             bound_modifier_allowed_features,
+                            hir_id,
                         ),
                     GenericArgsMode::Err => {
                         // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
@@ -398,13 +404,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
             );
         }
 
-        let res = self.expect_full_res(segment.id);
-        let hir_id = self.lower_node_id(segment.id);
         debug!(
             "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
             segment.ident, segment.id, hir_id,
         );
-
         hir::PathSegment {
             ident: self.lower_ident(segment.ident),
             hir_id,
@@ -508,13 +511,21 @@ impl<'hir> LoweringContext<'_, 'hir> {
         data: &ParenthesizedArgs,
         itctx: ImplTraitContext,
         bound_modifier_allowed_features: Option<Arc<[Symbol]>>,
+        segment_hir_id: HirId,
     ) -> (GenericArgsCtor<'hir>, bool) {
         // Switch to `PassThrough` mode for anonymous lifetimes; this
         // means that we permit things like `&Ref<T>`, where `Ref` has
         // a hidden lifetime parameter. This is needed for backwards
         // compatibility, even in contexts like an impl header where
         // we generally don't permit such things (see #51008).
         let ParenthesizedArgs { span, inputs, inputs_span, output } = data;
+
+        // FIXME uses the segments HIR id which is not correct, it should
+        // be the parameters HIR id instead. This is currently not lowered.
+        for input in inputs {
+            self.lower_attrs(segment_hir_id, &input.attrs, input.span, Target::Param);
+        }
+
         let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
             self.lower_ty(&param.ty, ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitParam))
         }));

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -399,7 +399,7 @@ impl<'a> AstValidator<'a> {
         self.check_decl_num_args(fn_decl);
         let c_variadic_span = self.check_decl_cvariadic_pos(fn_decl);
         self.check_decl_splatting(fn_decl, c_variadic_span, splat_semantic);
-        self.check_decl_attrs(fn_decl);
+        self.check_decl_attrs(&fn_decl.inputs);
         self.check_decl_self_param(&fn_decl.inputs, self_semantic);
         self.check_decl_const_param(&fn_decl.inputs);
     }
@@ -518,10 +518,9 @@ impl<'a> AstValidator<'a> {
         }
     }
 
-    fn check_decl_attrs(&self, fn_decl: &FnDecl) {
+    fn check_decl_attrs(&self, fn_inputs: &[Param]) {
         use SyntheticAttr::*;
-        fn_decl
-            .inputs
+        fn_inputs
             .iter()
             .flat_map(|i| i.attrs.as_ref())
             .filter(|attr| match &attr.kind {
@@ -2230,6 +2229,7 @@ impl Visitor<'_> for AstValidator<'_> {
     fn visit_path_segment(&mut self, seg: &PathSegment) -> Self::Result {
         if let Some(Parenthesized(args)) = &seg.args {
             self.check_decl_self_param(&args.inputs, SelfSemantic::No);
+            self.check_decl_attrs(&args.inputs);
             Self::check_decl_no_pat(&args.inputs, |span, _, _| {
                 self.dcx().emit_err(diagnostics::PatternParenthesizedArgList { span });
             });

compiler/rustc_parse/src/diagnostics.rs

@@ -2077,14 +2077,6 @@ pub(crate) struct PathFoundCVariadicParams {
     pub span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag("`Trait(...)` syntax does not support attributes in parameters")]
-pub(crate) struct PathFoundAttributeInParams {
-    #[primary_span]
-    #[suggestion("remove the attributes", applicability = "machine-applicable", code = "")]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag("path separator must be a double colon")]
 pub(crate) struct PathSingleColon {

compiler/rustc_parse/src/parser/path.rs

@@ -15,8 +15,8 @@ use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{Parser, Restrictions, TokenType};
 use crate::ast::{PatKind, TyKind};
 use crate::diagnostics::{
-    self, ConstGenericWithoutBraces, ConstGenericWithoutBracesSugg, PathFoundAttributeInParams,
-    PathFoundCVariadicParams, PathSingleColon, PathTripleColon,
+    self, ConstGenericWithoutBraces, ConstGenericWithoutBracesSugg, PathFoundCVariadicParams,
+    PathSingleColon, PathTripleColon,
 };
 use crate::exp;
 use crate::parser::{CommaRecoveryMode, Expr, FnContext, FnParseMode, RecoverColon, RecoverComma};
@@ -433,7 +433,9 @@ impl<'a> Parser<'a> {
                             dcx.emit_err(PathFoundCVariadicParams { span: param.pat.span });
                         }
                         if !param.attrs.is_empty() {
-                            dcx.emit_err(PathFoundAttributeInParams { span: param.attrs[0].span });
+                            self.psess
+                                .gated_spans
+                                .gate(sym::named_fn_trait_parameters, param.attrs[0].span);
                         }
                         Ok(param)
                     });

tests/ui/fn/fn-trait-use-named-params-issue-140169.rs

@@ -6,7 +6,13 @@ fn f4(_: impl Fn(aaaa: u8, vvvv: u8)) {}
 //~| ERROR named parameters in parenthesized generic argument lists are experimental
 fn f5(_: impl Fn(u8, ...)) {}
 //~^ ERROR `Trait(...)` syntax does not support c_variadic parameters
-fn f6(_: impl Fn(u8, #[allow(unused_attributes)] u8)) {}
-//~^ ERROR `Trait(...)` syntax does not support attributes in parameters
+fn f6(f: impl Fn(#[cfg(false)] u8)) { f() } //~ ERROR named parameters in parenthesized generic argument lists are experimental
+fn f7(_: impl Fn(#[inline] u8)) {}
+//~^ ERROR named parameters in parenthesized generic argument lists are experimental
+//~| ERROR the `inline` attribute cannot be used on function params
+//~| ERROR: allow, cfg, cfg_attr, deny, expect, forbid, and warn are the only allowed built-in attributes in function parameters
+fn f8(_: impl Fn(u8, #[allow(unused_attributes)] u8)) {}
+//~^ ERROR named parameters in parenthesized generic argument lists are experimental
+
 
 fn main(){}

tests/ui/fn/fn-trait-use-named-params-issue-140169.stderr

@@ -4,11 +4,11 @@ error: `Trait(...)` syntax does not support c_variadic parameters
 LL | fn f5(_: impl Fn(u8, ...)) {}
    |                      ^^^ help: remove the `...`
 
-error: `Trait(...)` syntax does not support attributes in parameters
-  --> $DIR/fn-trait-use-named-params-issue-140169.rs:9:22
+error: allow, cfg, cfg_attr, deny, expect, forbid, and warn are the only allowed built-in attributes in function parameters
+  --> $DIR/fn-trait-use-named-params-issue-140169.rs:10:18
    |
-LL | fn f6(_: impl Fn(u8, #[allow(unused_attributes)] u8)) {}
-   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the attributes
+LL | fn f7(_: impl Fn(#[inline] u8)) {}
+   |                  ^^^^^^^^^
 
 error[E0658]: named parameters in parenthesized generic argument lists are experimental
   --> $DIR/fn-trait-use-named-params-issue-140169.rs:2:22
@@ -50,6 +50,44 @@ LL | fn f4(_: impl Fn(aaaa: u8, vvvv: u8)) {}
    = help: add `#![feature(named_fn_trait_parameters)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 6 previous errors
+error[E0658]: named parameters in parenthesized generic argument lists are experimental
+  --> $DIR/fn-trait-use-named-params-issue-140169.rs:9:18
+   |
+LL | fn f6(f: impl Fn(#[cfg(false)] u8)) { f() }
+   |                  ^^^^^^^^^^^^^
+   |
+   = note: see issue #158499 <https://github.com/rust-lang/rust/issues/158499> for more information
+   = help: add `#![feature(named_fn_trait_parameters)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: named parameters in parenthesized generic argument lists are experimental
+  --> $DIR/fn-trait-use-named-params-issue-140169.rs:10:18
+   |
+LL | fn f7(_: impl Fn(#[inline] u8)) {}
+   |                  ^^^^^^^^^
+   |
+   = note: see issue #158499 <https://github.com/rust-lang/rust/issues/158499> for more information
+   = help: add `#![feature(named_fn_trait_parameters)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: named parameters in parenthesized generic argument lists are experimental
+  --> $DIR/fn-trait-use-named-params-issue-140169.rs:14:22
+   |
+LL | fn f8(_: impl Fn(u8, #[allow(unused_attributes)] u8)) {}
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #158499 <https://github.com/rust-lang/rust/issues/158499> for more information
+   = help: add `#![feature(named_fn_trait_parameters)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: the `inline` attribute cannot be used on function params
+  --> $DIR/fn-trait-use-named-params-issue-140169.rs:10:20
+   |
+LL | fn f7(_: impl Fn(#[inline] u8)) {}
+   |                    ^^^^^^
+   |
+   = help: the `inline` attribute can only be applied to functions
+
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0658`.

tests/ui/fn/fn-trait-use-named-params.rs

@@ -0,0 +1,23 @@
+#![feature(named_fn_trait_parameters)]
+
+fn f1(f: impl Fn(#[cfg(false)] x: u8)) { f() }
+fn f2(_: impl Fn(#[inline] x: u8)) {}
+//~^ ERROR the `inline` attribute cannot be used on function params
+//~| ERROR: allow, cfg, cfg_attr, deny, expect, forbid, and warn are the only allowed built-in attributes in function parameters
+fn f3(_: impl Fn(#[cfg_attr(true, inline)] a1: usize)) {}
+//~^ ERROR the `inline` attribute cannot be used on function params
+//~| ERROR: allow, cfg, cfg_attr, deny, expect, forbid, and warn are the only allowed built-in attributes in function parameters
+fn f4(_: impl Fn(/** */ x: u8)) {}
+//~^ ERROR documentation comments cannot be applied to function parameters
+
+fn f5(_: impl Fn(#[forbid(non_snake_case)] NON_SNAKE: u8)) {}
+fn f6(_: impl Fn(#[forbid(keyword_idents_2024)] gen: u8)) {}
+//~^ ERROR `gen` is a keyword in the 2024 edition [keyword_idents_2024]
+//~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2024!
+fn f7(_: impl Fn(#[allow(keyword_idents_2024)] gen: u8)) {}
+fn f8(_: fn(#[rustc_splat] a: usize)) {}
+//~^ ERROR the `rustc_splat` attribute is an experimental feature
+
+
+
+fn main(){}

tests/ui/fn/fn-trait-use-named-params.stderr

@@ -0,0 +1,62 @@
+error: `gen` is a keyword in the 2024 edition
+  --> $DIR/fn-trait-use-named-params.rs:14:49
+   |
+LL | fn f6(_: impl Fn(#[forbid(keyword_idents_2024)] gen: u8)) {}
+   |                                                 ^^^ help: you can use a raw identifier to stay compatible: `r#gen`
+   |
+   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2024!
+   = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/gen-keyword.html>
+note: the lint level is defined here
+  --> $DIR/fn-trait-use-named-params.rs:14:27
+   |
+LL | fn f6(_: impl Fn(#[forbid(keyword_idents_2024)] gen: u8)) {}
+   |                           ^^^^^^^^^^^^^^^^^^^
+
+error: allow, cfg, cfg_attr, deny, expect, forbid, and warn are the only allowed built-in attributes in function parameters
+  --> $DIR/fn-trait-use-named-params.rs:4:18
+   |
+LL | fn f2(_: impl Fn(#[inline] x: u8)) {}
+   |                  ^^^^^^^^^
+
+error: allow, cfg, cfg_attr, deny, expect, forbid, and warn are the only allowed built-in attributes in function parameters
+  --> $DIR/fn-trait-use-named-params.rs:7:35
+   |
+LL | fn f3(_: impl Fn(#[cfg_attr(true, inline)] a1: usize)) {}
+   |                                   ^^^^^^
+
+error: documentation comments cannot be applied to function parameters
+  --> $DIR/fn-trait-use-named-params.rs:10:18
+   |
+LL | fn f4(_: impl Fn(/** */ x: u8)) {}
+   |                  ^^^^^^ doc comments are not allowed here
+
+error: the `inline` attribute cannot be used on function params
+  --> $DIR/fn-trait-use-named-params.rs:4:20
+   |
+LL | fn f2(_: impl Fn(#[inline] x: u8)) {}
+   |                    ^^^^^^
+   |
+   = help: the `inline` attribute can only be applied to functions
+
+error: the `inline` attribute cannot be used on function params
+  --> $DIR/fn-trait-use-named-params.rs:7:35
+   |
+LL | fn f3(_: impl Fn(#[cfg_attr(true, inline)] a1: usize)) {}
+   |                                   ^^^^^^
+   |
+   = help: the `inline` attribute can only be applied to functions
+
+error[E0658]: the `rustc_splat` attribute is an experimental feature
+  --> $DIR/fn-trait-use-named-params.rs:18:15
+   |
+LL | fn f8(_: fn(#[rustc_splat] a: usize)) {}
+   |               ^^^^^^^^^^^
+   |
+   = note: see issue #153629 <https://github.com/rust-lang/rust/issues/153629> for more information
+   = help: add `#![feature(splat)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+   = note: the `rustc_splat` attribute is experimental
+
+error: aborting due to 7 previous errors
+
+For more information about this error, try `rustc --explain E0658`.