Add link to invalid repr error

Author: estebank

compiler/rustc_attr_parsing/messages.ftl

@@ -132,6 +132,7 @@ attr_parsing_unknown_version_literal =
 attr_parsing_unrecognized_repr_hint =
     unrecognized representation hint
     .help = valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+    .note = for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 attr_parsing_unstable_cfg_target_compact =
     compact `cfg(target(..))` is experimental and subject to change

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -498,6 +498,7 @@ pub(crate) struct ReprIdent {
 #[derive(Diagnostic)]
 #[diag(attr_parsing_unrecognized_repr_hint, code = E0552)]
 #[help]
+#[note]
 pub(crate) struct UnrecognizedReprHint {
     #[primary_span]
     pub span: Span,

tests/ui/attributes/invalid-reprs.stderr

@@ -26,6 +26,7 @@ LL |     let y = #[repr(uwu(4))]
    |                    ^^^^^^
    |
    = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 error: aborting due to 3 previous errors
 

tests/ui/issues/issue-43988.stderr

@@ -25,6 +25,7 @@ LL |     #[repr(nothing)]
    |            ^^^^^^^
    |
    = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 error[E0552]: unrecognized representation hint
   --> $DIR/issue-43988.rs:18:12
@@ -33,6 +34,7 @@ LL |     #[repr(something_not_real)]
    |            ^^^^^^^^^^^^^^^^^^
    |
    = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 error[E0539]: malformed `repr` attribute input
   --> $DIR/issue-43988.rs:24:5

tests/ui/repr/invalid_repr_list_help.stderr

@@ -5,6 +5,7 @@ LL | #[repr(uwu)]
    |        ^^^
    |
    = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 error[E0552]: unrecognized representation hint
   --> $DIR/invalid_repr_list_help.rs:6:8
@@ -13,6 +14,7 @@ LL | #[repr(uwu = "a")]
    |        ^^^^^^^^^
    |
    = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 error[E0552]: unrecognized representation hint
   --> $DIR/invalid_repr_list_help.rs:9:8
@@ -21,6 +23,7 @@ LL | #[repr(uwu(4))]
    |        ^^^^^^
    |
    = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 error[E0552]: unrecognized representation hint
   --> $DIR/invalid_repr_list_help.rs:14:8
@@ -29,6 +32,7 @@ LL | #[repr(uwu, u8)]
    |        ^^^
    |
    = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 error[E0552]: unrecognized representation hint
   --> $DIR/invalid_repr_list_help.rs:19:8
@@ -37,6 +41,7 @@ LL | #[repr(uwu)]
    |        ^^^
    |
    = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 error: unknown `doc` attribute `owo`
   --> $DIR/invalid_repr_list_help.rs:20:7