Clean up extend function of ReprParser

Author: JonathanBrouwer

compiler/rustc_attr_parsing/src/attributes/repr.rs

@@ -7,20 +7,20 @@ use crate::session_diagnostics::{self, IncorrectReprFormatGenericCause};
 
 /// Parse #[repr(...)] forms.
 ///
-/// Valid repr contents: any of the primitive integral type names (see
-/// `int_type_of_word`, below) to specify enum discriminant type; `C`, to use
-/// the same discriminant size that the corresponding C enum would or C
-/// structure layout, `packed` to remove padding, and `transparent` to delegate representation
-/// concerns to the only non-ZST field.
-// FIXME(jdonszelmann): is a vec the right representation here even? isn't it just a struct?
+/// Valid repr contents:
+/// * any of the primitive integral type names to specify enum discriminant type
+/// * `Rust`, to use the default `Rust` layout of the type
+/// * `C`, to use the same layout for the type that C would use
+/// * `align(...)`, to change the alignment requirements of the type
+/// * `packed`, to remove padding
+/// * `transparent`, to delegate representation concerns to the only non-ZST field.
 pub(crate) struct ReprParser;
 
 impl CombineAttributeParser for ReprParser {
     type Item = (ReprAttr, Span);
     const PATH: &[Symbol] = &[sym::repr];
     const CONVERT: ConvertFn<Self::Item> =
         |items, first_span| AttributeKind::Repr { reprs: items, first_span };
-    // FIXME(jdonszelmann): never used
     const TEMPLATE: AttributeTemplate = template!(
         List: &["C", "Rust", "transparent", "align(...)", "packed(...)", "<integer type>"],
         "https://doc.rust-lang.org/reference/type-layout.html#representations"
@@ -30,29 +30,24 @@ impl CombineAttributeParser for ReprParser {
         cx: &mut AcceptContext<'_, '_>,
         args: &ArgParser,
     ) -> impl IntoIterator<Item = Self::Item> {
-        let mut reprs = Vec::new();
-
         let Some(list) = cx.expect_list(args, cx.attr_span) else {
-            return reprs;
+            return vec![];
         };
 
         if list.is_empty() {
             let attr_span = cx.attr_span;
             cx.adcx().warn_empty_attribute(attr_span);
-            return reprs;
+            return vec![];
         }
 
+        let mut reprs = Vec::new();
         for param in list.mixed() {
-            if let Some(_) = param.as_lit() {
-                cx.emit_err(session_diagnostics::ReprIdent { span: cx.attr_span });
+            let Some(item) = param.meta_item() else {
+                cx.adcx().expected_identifier(param.span());
                 continue;
-            }
-
-            reprs.extend(
-                param.meta_item().and_then(|mi| parse_repr(cx, &mi)).map(|r| (r, param.span())),
-            );
+            };
+            reprs.extend(parse_repr(cx, &item).map(|r| (r, param.span())));
         }
-
         reprs
     }
 

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -484,13 +484,6 @@ pub(crate) struct InvalidAlignmentValue {
     pub error_part: String,
 }
 
-#[derive(Diagnostic)]
-#[diag("meta item in `repr` must be an identifier", code = E0565)]
-pub(crate) struct ReprIdent {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag("unrecognized representation hint", code = E0552)]
 #[help(

tests/ui/error-codes/E0565.stderr

@@ -1,8 +1,12 @@
-error[E0565]: meta item in `repr` must be an identifier
+error[E0565]: malformed `repr` attribute input
   --> $DIR/E0565.rs:2:1
    |
 LL | #[repr("C")]
-   | ^^^^^^^^^^^^
+   | ^^^^^^^---^^
+   |        |
+   |        expected a valid identifier here
+   |
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html#representations>
 
 error: aborting due to 1 previous error