better template for repr attributes

Author: jdonszelmann

compiler/rustc_attr_parsing/src/attributes/repr.rs

@@ -25,7 +25,8 @@ impl<S: Stage> CombineAttributeParser<S> for ReprParser {
     const PATH: &[Symbol] = &[sym::repr];
     const CONVERT: ConvertFn<Self::Item> = AttributeKind::Repr;
     // FIXME(jdonszelmann): never used
-    const TEMPLATE: AttributeTemplate = template!(List: "C");
+    const TEMPLATE: AttributeTemplate =
+        template!(List: "C | Rust | align(...) | packed(...) | <integer type> | transparent");
 
     fn extend<'c>(
         cx: &'c mut AcceptContext<'_, '_, S>,

tests/ui/issues/issue-43988.stderr

@@ -38,7 +38,7 @@ LL |     #[repr]
    |     ^^^^^^^
    |     |
    |     expected this to be a list
-   |     help: must be of the form: `#[repr(C)]`
+   |     help: must be of the form: `#[repr(C | Rust | align(...) | packed(...) | <integer type> | transparent)]`
 
 error[E0539]: malformed `inline` attribute input
   --> $DIR/issue-43988.rs:30:5
@@ -64,7 +64,7 @@ LL |     let _z = #[repr] 1;
    |              ^^^^^^^
    |              |
    |              expected this to be a list
-   |              help: must be of the form: `#[repr(C)]`
+   |              help: must be of the form: `#[repr(C | Rust | align(...) | packed(...) | <integer type> | transparent)]`
 
 error[E0518]: attribute should be applied to function or closure
   --> $DIR/issue-43988.rs:5:5

tests/ui/repr/repr.stderr

@@ -5,7 +5,7 @@ LL | #[repr]
    | ^^^^^^^
    | |
    | expected this to be a list
-   | help: must be of the form: `#[repr(C)]`
+   | help: must be of the form: `#[repr(C | Rust | align(...) | packed(...) | <integer type> | transparent)]`
 
 error[E0539]: malformed `repr` attribute input
   --> $DIR/repr.rs:4:1
@@ -14,7 +14,7 @@ LL | #[repr = "B"]
    | ^^^^^^^^^^^^^
    | |
    | expected this to be a list
-   | help: must be of the form: `#[repr(C)]`
+   | help: must be of the form: `#[repr(C | Rust | align(...) | packed(...) | <integer type> | transparent)]`
 
 error[E0539]: malformed `repr` attribute input
   --> $DIR/repr.rs:7:1
@@ -23,7 +23,7 @@ LL | #[repr = "C"]
    | ^^^^^^^^^^^^^
    | |
    | expected this to be a list
-   | help: must be of the form: `#[repr(C)]`
+   | help: must be of the form: `#[repr(C | Rust | align(...) | packed(...) | <integer type> | transparent)]`
 
 error: aborting due to 3 previous errors