Don't parse keyword as identifier when trying to diagnose

Author: mu001999

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -2261,6 +2261,7 @@ impl<'a> Parser<'a> {
         // If we find a pattern followed by an identifier, it could be an (incorrect)
         // C-style parameter declaration.
         if self.check_ident()
+            && self.token.is_non_reserved_ident()
             && self.look_ahead(1, |t| *t == token::Comma || *t == token::CloseParen)
         {
             // `fn foo(String s) {}`

tests/ui/parser/macro/kw-in-item-pos-recovery-151238.rs

@@ -0,0 +1,12 @@
+//@ edition: 2021
+
+macro_rules! x {
+    ($ty : item) => {};
+}
+x! {
+  trait MyTrait { fn bar(c self) }
+  //~^ ERROR expected one of `:`, `@`, or `|`, found keyword `self`
+  //~^^ ERROR expected one of `->`, `;`, `where`, or `{`, found `}`
+}
+
+fn main() {}

tests/ui/parser/macro/kw-in-item-pos-recovery-151238.stderr

@@ -0,0 +1,16 @@
+error: expected one of `:`, `@`, or `|`, found keyword `self`
+  --> $DIR/kw-in-item-pos-recovery-151238.rs:7:28
+   |
+LL |   trait MyTrait { fn bar(c self) }
+   |                            ^^^^ expected one of `:`, `@`, or `|`
+
+error: expected one of `->`, `;`, `where`, or `{`, found `}`
+  --> $DIR/kw-in-item-pos-recovery-151238.rs:7:34
+   |
+LL |   trait MyTrait { fn bar(c self) }
+   |                      ---         ^ expected one of `->`, `;`, `where`, or `{`
+   |                      |
+   |                      while parsing this `fn`
+
+error: aborting due to 2 previous errors
+