Rewrite target checking for #[link]

compiler/rustc_attr_parsing/src/attributes/link_attrs.rs

@@ -70,7 +70,8 @@ impl CombineAttributeParser for LinkParser {
             r#"name = "...", import_name_type = "decorated|noprefix|undecorated""#,
             r#"name = "...", kind = "dylib|static|...", wasm_import_module = "...", import_name_type = "decorated|noprefix|undecorated""#,
         ], "https://doc.rust-lang.org/reference/items/external-blocks.html#the-link-attribute");
-    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS); //FIXME Still checked fully in `check_attr.rs`
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowListWarnRest(&[Allow(Target::ForeignMod)]);
     const STABILITY: AttributeStability = AttributeStability::Stable;
 
     fn extend(

compiler/rustc_passes/src/check_attr.rs

@@ -230,7 +230,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             &AttributeKind::Sanitize { on_set, off_set, rtsan: _, span: attr_span } => {
                 self.check_sanitize(attr_span, on_set | off_set, span, target);
             }
-            AttributeKind::Link(_, attr_span) => self.check_link(hir_id, *attr_span, span, target),
+            AttributeKind::Link(_, attr_span) => self.check_link(hir_id, *attr_span, target),
             AttributeKind::MacroExport { span, .. } => {
                 self.check_macro_export(hir_id, *span, target)
             }
@@ -1126,21 +1126,19 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     }
 
     /// Checks if `#[link]` is applied to an item other than a foreign module.
-    fn check_link(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
-        if target == Target::ForeignMod
-            && let hir::Node::Item(item) = self.tcx.hir_node(hir_id)
+    fn check_link(&self, hir_id: HirId, attr_span: Span, target: Target) {
+        if target != Target::ForeignMod {
+            return; // Checked by attribute parser
+        }
+
+        if let hir::Node::Item(item) = self.tcx.hir_node(hir_id)
             && let Item { kind: ItemKind::ForeignMod { abi, .. }, .. } = item
             && !matches!(abi, ExternAbi::Rust)
         {
             return;
         }
 
-        self.tcx.emit_node_span_lint(
-            UNUSED_ATTRIBUTES,
-            hir_id,
-            attr_span,
-            errors::Link { span: (target != Target::ForeignMod).then_some(span) },
-        );
+        self.tcx.emit_node_span_lint(UNUSED_ATTRIBUTES, hir_id, attr_span, errors::Link);
     }
 
     /// Checks if `#[rustc_legacy_const_generics]` is applied to a function and has a valid argument.

compiler/rustc_passes/src/errors.rs

@@ -183,10 +183,7 @@ pub(crate) struct BothFfiConstAndPure {
 #[warning(
     "this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!"
 )]
-pub(crate) struct Link {
-    #[label("not an `extern` block")]
-    pub span: Option<Span>,
-}
+pub(crate) struct Link;
 
 #[derive(Diagnostic)]
 #[diag("#[rustc_legacy_const_generics] functions must only have const generics")]

tests/ui/attributes/attr-on-mac-call.rs

@@ -69,6 +69,9 @@ fn main() {
     #[should_panic]
     //~^ WARN attribute cannot be used on macro calls
     //~| WARN previously accepted
+    #[link_name = "x"]
+    //~^ WARN attribute cannot be used on macro calls
+    //~| WARN previously accepted
     unreachable!();
 
     #[repr()]

tests/ui/attributes/attr-on-mac-call.stderr

@@ -201,8 +201,17 @@ LL |     #[should_panic]
    = help: `#[should_panic]` can only be applied to functions
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
+warning: `#[link_name]` attribute cannot be used on macro calls
+  --> $DIR/attr-on-mac-call.rs:72:5
+   |
+LL |     #[link_name = "x"]
+   |     ^^^^^^^^^^^^^^^^^^
+   |
+   = help: `#[link_name]` can be applied to foreign functions and foreign statics
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
 warning: `#[repr()]` attribute cannot be used on macro calls
-  --> $DIR/attr-on-mac-call.rs:74:5
+  --> $DIR/attr-on-mac-call.rs:77:5
    |
 LL |     #[repr()]
    |     ^^^^^^^^^
@@ -211,15 +220,15 @@ LL |     #[repr()]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: unused attribute
-  --> $DIR/attr-on-mac-call.rs:74:5
+  --> $DIR/attr-on-mac-call.rs:77:5
    |
 LL |     #[repr()]
    |     ^^^^^^^^^ help: remove this attribute
    |
    = note: using `repr` with an empty list has no effect
 
 warning: `#[repr(u8)]` attribute cannot be used on macro calls
-  --> $DIR/attr-on-mac-call.rs:79:5
+  --> $DIR/attr-on-mac-call.rs:82:5
    |
 LL |     #[repr(u8)]
    |     ^^^^^^^^^^^
@@ -228,7 +237,7 @@ LL |     #[repr(u8)]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[repr(align(...))]` attribute cannot be used on macro calls
-  --> $DIR/attr-on-mac-call.rs:83:5
+  --> $DIR/attr-on-mac-call.rs:86:5
    |
 LL |     #[repr(align(8))]
    |     ^^^^^^^^^^^^^^^^^
@@ -237,7 +246,7 @@ LL |     #[repr(align(8))]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[repr(packed)]` attribute cannot be used on macro calls
-  --> $DIR/attr-on-mac-call.rs:87:5
+  --> $DIR/attr-on-mac-call.rs:90:5
    |
 LL |     #[repr(packed)]
    |     ^^^^^^^^^^^^^^^
@@ -246,7 +255,7 @@ LL |     #[repr(packed)]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[repr(C)]` attribute cannot be used on macro calls
-  --> $DIR/attr-on-mac-call.rs:91:5
+  --> $DIR/attr-on-mac-call.rs:94:5
    |
 LL |     #[repr(C)]
    |     ^^^^^^^^^^
@@ -255,7 +264,7 @@ LL |     #[repr(C)]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[repr(Rust)]` attribute cannot be used on macro calls
-  --> $DIR/attr-on-mac-call.rs:95:5
+  --> $DIR/attr-on-mac-call.rs:98:5
    |
 LL |     #[repr(Rust)]
    |     ^^^^^^^^^^^^^
@@ -264,13 +273,13 @@ LL |     #[repr(Rust)]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[repr(simd)]` attribute cannot be used on macro calls
-  --> $DIR/attr-on-mac-call.rs:99:5
+  --> $DIR/attr-on-mac-call.rs:102:5
    |
 LL |     #[repr(simd)]
    |     ^^^^^^^^^^^^^
    |
    = help: `#[repr(simd)]` can only be applied to structs
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
-warning: 30 warnings emitted
+warning: 31 warnings emitted
 

tests/ui/attributes/malformed-attrs.rs

@@ -80,7 +80,7 @@
 //~^ ERROR malformed
 #[link]
 //~^ ERROR malformed
-//~| WARN attribute should be applied to an `extern` block with non-Rust ABI
+//~| WARN attribute cannot be used on
 //~| WARN previously accepted
 #[link_name]
 //~^ ERROR malformed

tests/ui/attributes/malformed-attrs.stderr

@@ -814,21 +814,6 @@ LL | |     #[coroutine = 63] || {}
 LL | | }
    | |_- not a `const fn`
 
-warning: attribute should be applied to an `extern` block with non-Rust ABI
-  --> $DIR/malformed-attrs.rs:81:1
-   |
-LL |   #[link]
-   |   ^^^^^^^
-...
-LL | / fn test() {
-LL | |     #[coroutine = 63] || {}
-...  |
-LL | | }
-   | |_- not an `extern` block
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: requested on the command line with `-W unused-attributes`
-
 error: valid forms for the attribute are `#[doc = "string"]`, `#[doc(alias)]`, `#[doc(attribute)]`, `#[doc(auto_cfg)]`, `#[doc(cfg)]`, `#[doc(fake_variadic)]`, `#[doc(hidden)]`, `#[doc(html_favicon_url)]`, `#[doc(html_logo_url)]`, `#[doc(html_no_source)]`, `#[doc(html_playground_url)]`, `#[doc(html_root_url)]`, `#[doc(include)]`, `#[doc(inline)]`, `#[doc(issue_tracker_base_url)]`, `#[doc(keyword)]`, `#[doc(masked)]`, `#[doc(no_default_passes)]`, `#[doc(no_inline)]`, `#[doc(notable_trait)]`, `#[doc(passes)]`, `#[doc(plugins)]`, `#[doc(rust_logo)]`, `#[doc(search_unbox)]`, `#[doc(spotlight)]`, and `#[doc(test)]`
   --> $DIR/malformed-attrs.rs:41:1
    |
@@ -865,13 +850,23 @@ LL | |     #[coroutine = 63] || {}
 ...  |
 LL | | }
    | |_^
+   = note: requested on the command line with `-W unused-attributes`
 
 error: valid forms for the attribute are `#[doc = "string"]`, `#[doc(alias)]`, `#[doc(attribute)]`, `#[doc(auto_cfg)]`, `#[doc(cfg)]`, `#[doc(fake_variadic)]`, `#[doc(hidden)]`, `#[doc(html_favicon_url)]`, `#[doc(html_logo_url)]`, `#[doc(html_no_source)]`, `#[doc(html_playground_url)]`, `#[doc(html_root_url)]`, `#[doc(include)]`, `#[doc(inline)]`, `#[doc(issue_tracker_base_url)]`, `#[doc(keyword)]`, `#[doc(masked)]`, `#[doc(no_default_passes)]`, `#[doc(no_inline)]`, `#[doc(notable_trait)]`, `#[doc(passes)]`, `#[doc(plugins)]`, `#[doc(rust_logo)]`, `#[doc(search_unbox)]`, `#[doc(spotlight)]`, and `#[doc(test)]`
   --> $DIR/malformed-attrs.rs:75:1
    |
 LL | #[doc]
    | ^^^^^^
 
+warning: `#[link]` attribute cannot be used on functions
+  --> $DIR/malformed-attrs.rs:81:1
+   |
+LL | #[link]
+   | ^^^^^^^
+   |
+   = help: `#[link]` can only be applied to foreign modules
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
 warning: `#[link_name]` attribute cannot be used on functions
   --> $DIR/malformed-attrs.rs:85:1
    |

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

@@ -1,4 +1,3 @@
-//~ NOTE not an `extern` block
 // This test enumerates as many compiler-builtin ungated attributes as
 // possible (that is, all the mutually compatible ones), and checks
 // that we get "expected" (*) warnings for each in the various weird
@@ -67,8 +66,10 @@
 //~| WARN previously accepted
 //~| HELP can only be applied to
 //~| HELP remove the attribute
-#![link(name = "x")] //~ WARN attribute should be applied to an `extern` block
-//~^ WARN this was previously accepted
+#![link(name = "x")] //~ WARN attribute cannot be used on
+//~| WARN this was previously accepted
+//~| HELP can only be applied to foreign modules
+//~| HELP remove the attribute
 #![link_name = "1900"]
 //~^ WARN attribute cannot be used on
 //~| WARN previously accepted
@@ -683,35 +684,40 @@ mod link_section {
 // Note that this is a `check-pass` test, so it will never invoke the linker.
 
 #[link(name = "x")]
-//~^ WARN attribute should be applied to an `extern` block
+//~^ WARN attribute cannot be used on
 //~| WARN this was previously accepted
+//~| HELP can only be applied to foreign modules
+//~| HELP remove the attribute
 mod link {
-    //~^ NOTE not an `extern` block
-
     mod inner { #![link(name = "x")] }
-    //~^ WARN attribute should be applied to an `extern` block
+    //~^ WARN attribute cannot be used on
     //~| WARN this was previously accepted
-    //~| NOTE not an `extern` block
+    //~| HELP can only be applied to foreign modules
+    //~| HELP remove the attribute
 
     #[link(name = "x")] fn f() { }
-    //~^ WARN attribute should be applied to an `extern` block
+    //~^ WARN attribute cannot be used on
     //~| WARN this was previously accepted
-    //~| NOTE not an `extern` block
+    //~| HELP can only be applied to foreign modules
+    //~| HELP remove the attribute
 
     #[link(name = "x")] struct S;
-    //~^ WARN attribute should be applied to an `extern` block
+    //~^ WARN attribute cannot be used on
     //~| WARN this was previously accepted
-    //~| NOTE not an `extern` block
+    //~| HELP can only be applied to foreign modules
+    //~| HELP remove the attribute
 
     #[link(name = "x")] type T = S;
-    //~^ WARN attribute should be applied to an `extern` block
+    //~^ WARN attribute cannot be used on
     //~| WARN this was previously accepted
-    //~| NOTE not an `extern` block
+    //~| HELP can only be applied to foreign modules
+    //~| HELP remove the attribute
 
     #[link(name = "x")] impl S { }
-    //~^ WARN attribute should be applied to an `extern` block
+    //~^ WARN attribute cannot be used on
     //~| WARN this was previously accepted
-    //~| NOTE not an `extern` block
+    //~| HELP can only be applied to foreign modules
+    //~| HELP remove the attribute
 
     #[link(name = "x")] extern "Rust" {}
     //~^ WARN attribute should be applied to an `extern` block