Unrolled build for #148756

Rollup merge of #148756 - JonathanBrouwer:link_section_targets2, r=jdonszelmann

Warn on codegen attributes on required trait methods

This PR turns applying the following attributes on required trait methods (that is, trait methods **without** a default implementation) into a FCW:
- `#[cold]`
- `#[link_section]`
- `#[linkage]` (unstable)
- `#[rustc_allow_const_fn_unstable]` (internal attribute)

These attributes already had no effect when applied to a required trait method, this PR only adds a warning.

Furthermore, it adds a comment in the code that the following codegen attributes are *inherited* when applied to a required trait method:
- `#[track_caller]`
- `#[align]` (unstable)

````@rustbot```` labels +I-lang-nominated
````@rust-lang/lang````

Two questions for the lang team:
- Is adding this warning ok?
- Does the current behaviour of these attributes align with that you would expect them to be?

Fixes #147432

Author: rust-timer

compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs

@@ -61,7 +61,6 @@ impl<S: Stage> CombineAttributeParser<S> for AllowConstFnUnstableParser {
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
         Allow(Target::Fn),
         Allow(Target::Method(MethodKind::Inherent)),
-        Allow(Target::Method(MethodKind::Trait { body: false })),
         Allow(Target::Method(MethodKind::Trait { body: true })),
         Allow(Target::Method(MethodKind::TraitImpl)),
     ]);

compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

@@ -57,7 +57,6 @@ impl<S: Stage> NoArgsAttributeParser<S> for ColdParser {
         Allow(Target::Fn),
         Allow(Target::Method(MethodKind::Trait { body: true })),
         Allow(Target::Method(MethodKind::TraitImpl)),
-        Allow(Target::Method(MethodKind::Trait { body: false })),
         Allow(Target::Method(MethodKind::Inherent)),
         Allow(Target::ForeignFn),
         Allow(Target::Closure),
@@ -343,7 +342,7 @@ impl<S: Stage> NoArgsAttributeParser<S> for TrackCallerParser {
         Allow(Target::Method(MethodKind::Inherent)),
         Allow(Target::Method(MethodKind::Trait { body: true })),
         Allow(Target::Method(MethodKind::TraitImpl)),
-        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Trait { body: false })), // `#[track_caller]` is inherited from trait methods
         Allow(Target::ForeignFn),
         Allow(Target::Closure),
         Warn(Target::MacroDef),

compiler/rustc_attr_parsing/src/attributes/link_attrs.rs

@@ -469,7 +469,6 @@ impl<S: Stage> SingleAttributeParser<S> for LinkSectionParser {
         Allow(Target::Static),
         Allow(Target::Fn),
         Allow(Target::Method(MethodKind::Inherent)),
-        Allow(Target::Method(MethodKind::Trait { body: false })),
         Allow(Target::Method(MethodKind::Trait { body: true })),
         Allow(Target::Method(MethodKind::TraitImpl)),
     ]);
@@ -587,12 +586,12 @@ impl<S: Stage> SingleAttributeParser<S> for LinkageParser {
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
         Allow(Target::Fn),
         Allow(Target::Method(MethodKind::Inherent)),
-        Allow(Target::Method(MethodKind::Trait { body: false })),
         Allow(Target::Method(MethodKind::Trait { body: true })),
         Allow(Target::Method(MethodKind::TraitImpl)),
         Allow(Target::Static),
         Allow(Target::ForeignStatic),
         Allow(Target::ForeignFn),
+        Warn(Target::Method(MethodKind::Trait { body: false })), // Not inherited
     ]);
 
     const TEMPLATE: AttributeTemplate = template!(NameValueStr: [

compiler/rustc_attr_parsing/src/attributes/repr.rs

@@ -315,7 +315,7 @@ impl<S: Stage> AttributeParser<S> for AlignParser {
         Allow(Target::Method(MethodKind::Inherent)),
         Allow(Target::Method(MethodKind::Trait { body: true })),
         Allow(Target::Method(MethodKind::TraitImpl)),
-        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Trait { body: false })), // `#[align]` is inherited from trait methods
         Allow(Target::ForeignFn),
     ]);
 

tests/ui/attributes/codegen_attr_on_required_trait_method.rs

@@ -0,0 +1,24 @@
+#![deny(unused_attributes)]
+#![feature(linkage)]
+#![feature(fn_align)]
+
+trait Test {
+    #[cold]
+    //~^ ERROR cannot be used on required trait methods [unused_attributes]
+    //~| WARN previously accepted
+    fn method1(&self);
+    #[link_section = ".text"]
+    //~^ ERROR cannot be used on required trait methods [unused_attributes]
+    //~| WARN previously accepted
+    fn method2(&self);
+    #[linkage = "common"]
+    //~^ ERROR cannot be used on required trait methods [unused_attributes]
+    //~| WARN previously accepted
+    fn method3(&self);
+    #[track_caller]
+    fn method4(&self);
+    #[rustc_align(1)]
+    fn method5(&self);
+}
+
+fn main() {}

tests/ui/attributes/codegen_attr_on_required_trait_method.stderr

@@ -0,0 +1,34 @@
+error: `#[cold]` attribute cannot be used on required trait methods
+  --> $DIR/codegen_attr_on_required_trait_method.rs:6:5
+   |
+LL |     #[cold]
+   |     ^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = help: `#[cold]` can be applied to closures, foreign functions, functions, inherent methods, provided trait methods, and trait methods in impl blocks
+note: the lint level is defined here
+  --> $DIR/codegen_attr_on_required_trait_method.rs:1:9
+   |
+LL | #![deny(unused_attributes)]
+   |         ^^^^^^^^^^^^^^^^^
+
+error: `#[link_section]` attribute cannot be used on required trait methods
+  --> $DIR/codegen_attr_on_required_trait_method.rs:10:5
+   |
+LL |     #[link_section = ".text"]
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = help: `#[link_section]` can be applied to functions, inherent methods, provided trait methods, statics, and trait methods in impl blocks
+
+error: `#[linkage]` attribute cannot be used on required trait methods
+  --> $DIR/codegen_attr_on_required_trait_method.rs:14:5
+   |
+LL |     #[linkage = "common"]
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = help: `#[linkage]` can be applied to foreign functions, foreign statics, functions, inherent methods, provided trait methods, statics, and trait methods in impl blocks
+
+error: aborting due to 3 previous errors
+

tests/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs

@@ -680,6 +680,10 @@ mod link_section {
     //~| HELP remove the attribute
     trait Tr {
         #[link_section = "1800"]
+        //~^ WARN attribute cannot be used on
+        //~| WARN previously accepted
+        //~| HELP can be applied to
+        //~| HELP remove the attribute
         fn inside_tr_no_default(&self);
 
         #[link_section = "1800"]