Properly emit expected ; on #[attr] expr

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -800,9 +800,8 @@ impl<'a> Parser<'a> {
                 {
                     Ok(next_attr) => next_attr,
                     Err(inner_err) => {
-                        err.cancel();
                         inner_err.cancel();
-                        return self.dcx().span_delayed_bug(expr.span, "not a tail expression");
+                        return err.emit();
                     }
                 }
                 && let ast::AttrKind::Normal(next_attr_kind) = next_attr.kind
@@ -813,9 +812,8 @@ impl<'a> Parser<'a> {
                 let next_expr = match snapshot.parse_expr() {
                     Ok(next_expr) => next_expr,
                     Err(inner_err) => {
-                        err.cancel();
                         inner_err.cancel();
-                        return self.dcx().span_delayed_bug(expr.span, "not a tail expression");
+                        return err.emit();
                     }
                 };
                 // We have for sure

tests/ui/parser/attribute/properly-recover-from-trailing-outer-attribute-in-body-1.stderr

@@ -1,5 +1,5 @@
 error: expected `;`, found `#`
-  --> $DIR/properly-recover-from-trailing-outer-attribute-in-body.rs:4:47
+  --> $DIR/properly-recover-from-trailing-outer-attribute-in-body-1.rs:4:47
    |
 LL |     #[cfg(feature = )]
    |     ------------------ only `;` terminated statements or tail expressions are allowed after this attribute
@@ -18,7 +18,7 @@ LL |     { [1, 2, 3].iter().map().collect::<String>() }
    |     +                                            +
 
 error: expected statement after outer attribute
-  --> $DIR/properly-recover-from-trailing-outer-attribute-in-body.rs:5:5
+  --> $DIR/properly-recover-from-trailing-outer-attribute-in-body-1.rs:5:5
    |
 LL |     #[attr]
    |     ^^^^^^^

tests/ui/parser/attribute/properly-recover-from-trailing-outer-attribute-in-body-2.rs

@@ -0,0 +1,15 @@
+// Issue #121647: recovery path leaving unemitted error behind
+
+macro_rules! the_macro {
+    ( $foo:stmt ; $bar:stmt ; ) => {
+        #[cfg()]
+        $foo //~ ERROR expected `;`, found `#`
+
+        #[cfg(bar)]
+        $bar
+    };
+}
+
+fn main() {
+    the_macro!( (); (); );
+}

tests/ui/parser/attribute/properly-recover-from-trailing-outer-attribute-in-body-2.stderr

@@ -0,0 +1,26 @@
+error: expected `;`, found `#`
+  --> $DIR/properly-recover-from-trailing-outer-attribute-in-body-2.rs:6:13
+   |
+LL |         #[cfg()]
+   |         -------- only `;` terminated statements or tail expressions are allowed after this attribute
+LL |         $foo
+   |             ^ expected `;` here
+LL |
+LL |         #[cfg(bar)]
+   |         - unexpected token
+...
+LL |     the_macro!( (); (); );
+   |     --------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `the_macro` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: add `;` here
+   |
+LL |         $foo;
+   |             +
+help: alternatively, consider surrounding the expression with a block
+   |
+LL |     the_macro!( { () }; (); );
+   |                 +    +
+
+error: aborting due to 1 previous error
+