Rollup merge of #128989 - s7tya:check-linkage-attribute-pos, r=petrochenkov

Emit an error for invalid use of the linkage attribute

fixes #128486

Currently, the use of the linkage attribute for Mod, Impl,... is incorrectly permitted. This PR will correct this issue by generating errors, and I've also added some UI test cases for it.

Related: #128552.

compiler/rustc_passes/messages.ftl

@@ -430,6 +430,10 @@ passes_link_section =
     .warn = {-passes_previously_accepted}
     .label = not a function or static
 
+passes_linkage =
+    attribute should be applied to a function or static
+    .label = not a function definition or static
+
 passes_macro_export =
     `#[macro_export]` only has an effect on macro definitions
 

compiler/rustc_passes/src/check_attr.rs

@@ -243,6 +243,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 [sym::coroutine, ..] => {
                     self.check_coroutine(attr, target);
                 }
+                [sym::linkage, ..] => self.check_linkage(attr, span, target),
                 [
                     // ok
                     sym::allow
@@ -256,7 +257,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | sym::cfi_encoding // FIXME(cfi_encoding)
                     | sym::may_dangle // FIXME(dropck_eyepatch)
                     | sym::pointee // FIXME(derive_smart_pointer)
-                    | sym::linkage // FIXME(linkage)
                     | sym::omit_gdb_pretty_printer_section // FIXME(omit_gdb_pretty_printer_section)
                     | sym::used // handled elsewhere to restrict to static items
                     | sym::repr // handled elsewhere to restrict to type decls items
@@ -2347,6 +2347,19 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             }
         }
     }
+
+    fn check_linkage(&self, attr: &Attribute, span: Span, target: Target) {
+        match target {
+            Target::Fn
+            | Target::Method(..)
+            | Target::Static
+            | Target::ForeignStatic
+            | Target::ForeignFn => {}
+            _ => {
+                self.dcx().emit_err(errors::Linkage { attr_span: attr.span, span });
+            }
+        }
+    }
 }
 
 impl<'tcx> Visitor<'tcx> for CheckAttrVisitor<'tcx> {

compiler/rustc_passes/src/errors.rs

@@ -643,6 +643,15 @@ pub struct CoroutineOnNonClosure {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(passes_linkage)]
+pub struct Linkage {
+    #[primary_span]
+    pub attr_span: Span,
+    #[label]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(passes_empty_confusables)]
 pub(crate) struct EmptyConfusables {

tests/ui/attributes/linkage.rs

@@ -0,0 +1,42 @@
+#![feature(linkage)]
+#![feature(stmt_expr_attributes)]
+#![deny(unused_attributes)]
+#![allow(dead_code)]
+
+#[linkage = "weak"] //~ ERROR attribute should be applied to a function or static
+type InvalidTy = ();
+
+#[linkage = "weak"] //~ ERROR attribute should be applied to a function or static
+mod invalid_module {}
+
+#[linkage = "weak"] //~ ERROR attribute should be applied to a function or static
+struct F;
+
+#[linkage = "weak"] //~ ERROR attribute should be applied to a function or static
+impl F {
+    #[linkage = "weak"]
+    fn valid(&self) {}
+}
+
+#[linkage = "weak"]
+fn f() {
+    #[linkage = "weak"]
+    {
+        1
+    };
+    //~^^^^ ERROR attribute should be applied to a function or static
+}
+
+extern "C" {
+    #[linkage = "weak"]
+    static A: *const ();
+
+    #[linkage = "weak"]
+    fn bar();
+}
+
+fn main() {
+    let _ = #[linkage = "weak"]
+    (|| 1);
+    //~^^ ERROR attribute should be applied to a function or static
+}

tests/ui/attributes/linkage.stderr

@@ -0,0 +1,55 @@
+error: attribute should be applied to a function or static
+  --> $DIR/linkage.rs:6:1
+   |
+LL | #[linkage = "weak"]
+   | ^^^^^^^^^^^^^^^^^^^
+LL | type InvalidTy = ();
+   | -------------------- not a function definition or static
+
+error: attribute should be applied to a function or static
+  --> $DIR/linkage.rs:9:1
+   |
+LL | #[linkage = "weak"]
+   | ^^^^^^^^^^^^^^^^^^^
+LL | mod invalid_module {}
+   | --------------------- not a function definition or static
+
+error: attribute should be applied to a function or static
+  --> $DIR/linkage.rs:12:1
+   |
+LL | #[linkage = "weak"]
+   | ^^^^^^^^^^^^^^^^^^^
+LL | struct F;
+   | --------- not a function definition or static
+
+error: attribute should be applied to a function or static
+  --> $DIR/linkage.rs:15:1
+   |
+LL |   #[linkage = "weak"]
+   |   ^^^^^^^^^^^^^^^^^^^
+LL | / impl F {
+LL | |     #[linkage = "weak"]
+LL | |     fn valid(&self) {}
+LL | | }
+   | |_- not a function definition or static
+
+error: attribute should be applied to a function or static
+  --> $DIR/linkage.rs:23:5
+   |
+LL |       #[linkage = "weak"]
+   |       ^^^^^^^^^^^^^^^^^^^
+LL | /     {
+LL | |         1
+LL | |     };
+   | |_____- not a function definition or static
+
+error: attribute should be applied to a function or static
+  --> $DIR/linkage.rs:39:13
+   |
+LL |     let _ = #[linkage = "weak"]
+   |             ^^^^^^^^^^^^^^^^^^^
+LL |     (|| 1);
+   |     ------ not a function definition or static
+
+error: aborting due to 6 previous errors
+