Keep items around even if builtin macros on them fail to parse

Author: oli-obk

Diff for: compiler/rustc_expand/src/expand.rs

@@ -780,8 +780,8 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                             }
                         }
                         Err(err) => {
-                            let guar = err.emit();
-                            fragment_kind.dummy(span, guar)
+                            let _guar = err.emit();
+                            fragment_kind.expect_from_annotatables(iter::once(item))
                         }
                     }
                 }

Diff for: tests/ui/type-alias-impl-trait/define_opaques_attr/generics.rs

@@ -10,4 +10,3 @@ fn foo() {}
 #[define_opaque(Tait<()>)]
 //~^ ERROR: expected one of `(`, `,`, `::`, or `=`, found `<`
 fn main() {}
-//~^ ERROR: `main` function not found

Diff for: tests/ui/type-alias-impl-trait/define_opaques_attr/generics.stderr

@@ -10,12 +10,6 @@ error: expected one of `(`, `,`, `::`, or `=`, found `<`
 LL | #[define_opaque(Tait<()>)]
    |                     ^ expected one of `(`, `,`, `::`, or `=`
 
-error[E0601]: `main` function not found in crate `generics`
-  --> $DIR/generics.rs:12:13
-   |
-LL | fn main() {}
-   |             ^ consider adding a `main` function to `$DIR/generics.rs`
-
 error: unconstrained opaque type
   --> $DIR/generics.rs:3:16
    |
@@ -24,6 +18,5 @@ LL | type Tait<T> = impl Sized;
    |
    = note: `Tait` must be used in combination with a concrete type within the same crate
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0601`.