Add checks for more empty attributes.

compiler/rustc_passes/src/check_attr.rs

@@ -173,8 +173,17 @@ impl CheckAttrVisitor<'tcx> {
             }
 
             // Warn on useless empty attributes.
-            if matches!(attr.name_or_empty(), sym::macro_use)
-                && attr.meta_item_list().map_or(false, |list| list.is_empty())
+            if matches!(
+                attr.name_or_empty(),
+                sym::macro_use
+                    | sym::allow
+                    | sym::warn
+                    | sym::deny
+                    | sym::forbid
+                    | sym::feature
+                    | sym::repr
+                    | sym::target_feature
+            ) && attr.meta_item_list().map_or(false, |list| list.is_empty())
             {
                 self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
                     lint.build("unused attribute")

src/test/ui/empty/empty-attributes.rs

@@ -0,0 +1,14 @@
+#![deny(unused_attributes)]
+#![allow()] //~ ERROR unused attribute
+#![warn()] //~ ERROR unused attribute
+#![deny()] //~ ERROR unused attribute
+#![forbid()] //~ ERROR unused attribute
+#![feature()] //~ ERROR unused attribute
+
+#[repr()] //~ ERROR unused attribute
+pub struct S;
+
+#[target_feature()] //~ ERROR unused attribute
+pub unsafe fn foo() {}
+
+fn main() {}

src/test/ui/empty/empty-attributes.stderr

@@ -0,0 +1,63 @@
+error: unused attribute
+  --> $DIR/empty-attributes.rs:8:1
+   |
+LL | #[repr()]
+   | ^^^^^^^^^ help: remove this attribute
+   |
+note: the lint level is defined here
+  --> $DIR/empty-attributes.rs:1:9
+   |
+LL | #![deny(unused_attributes)]
+   |         ^^^^^^^^^^^^^^^^^
+   = note: attribute `repr` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:11:1
+   |
+LL | #[target_feature()]
+   | ^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `target_feature` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:2:1
+   |
+LL | #![allow()]
+   | ^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `allow` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:3:1
+   |
+LL | #![warn()]
+   | ^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `warn` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:4:1
+   |
+LL | #![deny()]
+   | ^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `deny` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:5:1
+   |
+LL | #![forbid()]
+   | ^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `forbid` with an empty list has no effect
+
+error: unused attribute
+  --> $DIR/empty-attributes.rs:6:1
+   |
+LL | #![feature()]
+   | ^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: attribute `feature` with an empty list has no effect
+
+error: aborting due to 7 previous errors
+

src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.rs

@@ -134,4 +134,27 @@ mod start {
     //~^ ERROR: `start` attribute can only be used on functions
 }
 
+#[repr(C)]
+//~^ ERROR: attribute should be applied to a struct, enum, or union
+mod repr {
+//~^ NOTE not a struct, enum, or union
+    mod inner { #![repr(C)] }
+    //~^ ERROR: attribute should be applied to a struct, enum, or union
+    //~| NOTE not a struct, enum, or union
+
+    #[repr(C)] fn f() { }
+    //~^ ERROR: attribute should be applied to a struct, enum, or union
+    //~| NOTE not a struct, enum, or union
+
+    struct S;
+
+    #[repr(C)] type T = S;
+    //~^ ERROR: attribute should be applied to a struct, enum, or union
+    //~| NOTE not a struct, enum, or union
+
+    #[repr(C)] impl S { }
+    //~^ ERROR: attribute should be applied to a struct, enum, or union
+    //~| NOTE not a struct, enum, or union
+}
+
 fn main() {}

src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs-error.stderr

@@ -91,6 +91,21 @@ LL | |     }
 LL | | }
    | |_- not a free function, impl method or static
 
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:137:8
+   |
+LL |   #[repr(C)]
+   |          ^
+LL |
+LL | / mod repr {
+LL | |
+LL | |     mod inner { #![repr(C)] }
+LL | |
+...  |
+LL | |
+LL | | }
+   | |_- not a struct, enum, or union
+
 error: attribute should be applied to an `extern crate` item
   --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:25:1
    |
@@ -235,7 +250,31 @@ error: attribute should be applied to a free function, impl method or static
 LL |         #[export_name = "2200"] fn bar() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^ ----------- not a free function, impl method or static
 
-error: aborting due to 34 previous errors
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:141:25
+   |
+LL |     mod inner { #![repr(C)] }
+   |     --------------------^---- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:145:12
+   |
+LL |     #[repr(C)] fn f() { }
+   |            ^   ---------- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:151:12
+   |
+LL |     #[repr(C)] type T = S;
+   |            ^   ----------- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-43106-gating-of-builtin-attrs-error.rs:155:12
+   |
+LL |     #[repr(C)] impl S { }
+   |            ^   ---------- not a struct, enum, or union
+
+error: aborting due to 39 previous errors
 
-Some errors have detailed explanations: E0518, E0658.
-For more information about an error, try `rustc --explain E0518`.
+Some errors have detailed explanations: E0517, E0518, E0658.
+For more information about an error, try `rustc --explain E0517`.

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

@@ -245,19 +245,6 @@ mod bench {
     impl S { }
 }
 
-#[repr()]
-mod repr {
-    mod inner { #![repr()] }
-
-    #[repr()] fn f() { }
-
-    struct S;
-
-    #[repr()] type T = S;
-
-    #[repr()] impl S { }
-}
-
 #[path = "3800"]
 mod path {
     mod inner { #![path="3800"] }