Rollup merge of #78379 - estebank:fn-signature-parse, r=varkor

Tweak invalid `fn` header and body parsing

* Rely on regular "expected"/"found" parser error for `fn`, fix #77115
* Recover empty `fn` bodies when encountering `}`
* Recover trailing `>` in return types
* Recover from non-type in array type `[<BAD TOKEN>; LEN]`

1 files changed, 13 insertions, 1 deletions

diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index d42a786a18f..7a6ebca4e15 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -265,7 +265,19 @@ impl<'a> Parser<'a> {
     /// Parses an array (`[TYPE; EXPR]`) or slice (`[TYPE]`) type.
     /// The opening `[` bracket is already eaten.
     fn parse_array_or_slice_ty(&mut self) -> PResult<'a, TyKind> {
-        let elt_ty = self.parse_ty()?;
+        let elt_ty = match self.parse_ty() {
+            Ok(ty) => ty,
+            Err(mut err)
+                if self.look_ahead(1, |t| t.kind == token::CloseDelim(token::Bracket))
+                    | self.look_ahead(1, |t| t.kind == token::Semi) =>
+            {
+                // Recover from `[LIT; EXPR]` and `[LIT]`
+                self.bump();
+                err.emit();
+                self.mk_ty(self.prev_token.span, TyKind::Err)
+            }
+            Err(err) => return Err(err),
+        };
         let ty = if self.eat(&token::Semi) {
             TyKind::Array(elt_ty, self.parse_anon_const_expr()?)
         } else {