passes: prohibit attrs on generic params

This commit modifies the `check_attr` pass so that attribute placement
on generic parameters is checked for validity.

Signed-off-by: David Wood <david@davidtw.co>

src/test/ui/issues/issue-78957.rs

@@ -0,0 +1,30 @@
+#![deny(unused_attributes)]
+#![feature(min_const_generics)]
+
+use std::marker::PhantomData;
+
+pub struct Foo<#[inline] const N: usize>;
+//~^ ERROR attribute should be applied to function or closure
+pub struct Bar<#[cold] const N: usize>;
+//~^ ERROR attribute should be applied to a function
+//~| WARN this was previously accepted
+pub struct Baz<#[repr(C)] const N: usize>;
+//~^ ERROR attribute should be applied to a struct, enum, or union
+//
+pub struct Foo2<#[inline] 'a>(PhantomData<&'a ()>);
+//~^ ERROR attribute should be applied to function or closure
+pub struct Bar2<#[cold] 'a>(PhantomData<&'a ()>);
+//~^ ERROR attribute should be applied to a function
+//~| WARN this was previously accepted
+pub struct Baz2<#[repr(C)] 'a>(PhantomData<&'a ()>);
+//~^ ERROR attribute should be applied to a struct, enum, or union
+//
+pub struct Foo3<#[inline] T>(PhantomData<T>);
+//~^ ERROR attribute should be applied to function or closure
+pub struct Bar3<#[cold] T>(PhantomData<T>);
+//~^ ERROR attribute should be applied to a function
+//~| WARN this was previously accepted
+pub struct Baz3<#[repr(C)] T>(PhantomData<T>);
+//~^ ERROR attribute should be applied to a struct, enum, or union
+
+fn main() {}

src/test/ui/issues/issue-78957.stderr

@@ -0,0 +1,69 @@
+error[E0518]: attribute should be applied to function or closure
+  --> $DIR/issue-78957.rs:6:16
+   |
+LL | pub struct Foo<#[inline] const N: usize>;
+   |                ^^^^^^^^^       - not a function or closure
+
+error: attribute should be applied to a function
+  --> $DIR/issue-78957.rs:8:16
+   |
+LL | pub struct Bar<#[cold] const N: usize>;
+   |                ^^^^^^^       - not a function
+   |
+note: the lint level is defined here
+  --> $DIR/issue-78957.rs:1:9
+   |
+LL | #![deny(unused_attributes)]
+   |         ^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-78957.rs:11:23
+   |
+LL | pub struct Baz<#[repr(C)] const N: usize>;
+   |                       ^         - not a struct, enum, or union
+
+error[E0518]: attribute should be applied to function or closure
+  --> $DIR/issue-78957.rs:14:17
+   |
+LL | pub struct Foo2<#[inline] 'a>(PhantomData<&'a ()>);
+   |                 ^^^^^^^^^ -- not a function or closure
+
+error: attribute should be applied to a function
+  --> $DIR/issue-78957.rs:16:17
+   |
+LL | pub struct Bar2<#[cold] 'a>(PhantomData<&'a ()>);
+   |                 ^^^^^^^ -- not a function
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-78957.rs:19:24
+   |
+LL | pub struct Baz2<#[repr(C)] 'a>(PhantomData<&'a ()>);
+   |                        ^   -- not a struct, enum, or union
+
+error[E0518]: attribute should be applied to function or closure
+  --> $DIR/issue-78957.rs:22:17
+   |
+LL | pub struct Foo3<#[inline] T>(PhantomData<T>);
+   |                 ^^^^^^^^^ - not a function or closure
+
+error: attribute should be applied to a function
+  --> $DIR/issue-78957.rs:24:17
+   |
+LL | pub struct Bar3<#[cold] T>(PhantomData<T>);
+   |                 ^^^^^^^ - not a function
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/issue-78957.rs:27:24
+   |
+LL | pub struct Baz3<#[repr(C)] T>(PhantomData<T>);
+   |                        ^   - not a struct, enum, or union
+
+error: aborting due to 9 previous errors
+
+Some errors have detailed explanations: E0517, E0518.
+For more information about an error, try `rustc --explain E0517`.

src/test/ui/proc-macro/ambiguous-builtin-attrs.rs

@@ -17,7 +17,9 @@ fn test() {}
 #[bench] // OK, shadowed
 fn bench() {}
 
-fn non_macro_expanded_location<#[repr(C)] T>() { //~ ERROR `repr` is ambiguous
+fn non_macro_expanded_location<#[repr(C)] T>() {
+    //~^ ERROR `repr` is ambiguous
+    //~| ERROR attribute should be applied to a struct, enum, or union
     match 0u8 {
         #[repr(C)] //~ ERROR `repr` is ambiguous
         _ => {}

src/test/ui/proc-macro/ambiguous-builtin-attrs.stderr

@@ -1,5 +1,5 @@
 error[E0425]: cannot find value `NonExistent` in this scope
-  --> $DIR/ambiguous-builtin-attrs.rs:30:5
+  --> $DIR/ambiguous-builtin-attrs.rs:32:5
    |
 LL |     NonExistent;
    |     ^^^^^^^^^^^ not found in this scope
@@ -47,7 +47,7 @@ LL | use builtin_attrs::*;
    = help: use `crate::repr` to refer to this attribute macro unambiguously
 
 error[E0659]: `repr` is ambiguous (built-in attribute vs any other name)
-  --> $DIR/ambiguous-builtin-attrs.rs:22:11
+  --> $DIR/ambiguous-builtin-attrs.rs:24:11
    |
 LL |         #[repr(C)]
    |           ^^^^ ambiguous name
@@ -74,7 +74,13 @@ LL | use builtin_attrs::*;
    |     ^^^^^^^^^^^^^^^^
    = help: use `crate::feature` to refer to this attribute macro unambiguously
 
-error: aborting due to 6 previous errors
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/ambiguous-builtin-attrs.rs:20:39
+   |
+LL | fn non_macro_expanded_location<#[repr(C)] T>() {
+   |                                       ^   - not a struct, enum, or union
 
-Some errors have detailed explanations: E0425, E0659.
+error: aborting due to 7 previous errors
+
+Some errors have detailed explanations: E0425, E0517, E0659.
 For more information about an error, try `rustc --explain E0425`.