fix: emit error when fragment is MethodReceiverExpr and items is empty

Author: bvanjoi

compiler/rustc_expand/src/expand.rs

@@ -722,7 +722,11 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                                     });
                                 }
                             };
-                            if fragment_kind == AstFragmentKind::Expr && items.is_empty() {
+                            if matches!(
+                                fragment_kind,
+                                AstFragmentKind::Expr | AstFragmentKind::MethodReceiverExpr
+                            ) && items.is_empty()
+                            {
                                 self.cx.emit_err(RemoveExprNotSupported { span });
                                 fragment_kind.dummy(span)
                             } else {

tests/ui/macros/issue-111749.rs

@@ -0,0 +1,12 @@
+macro_rules! cbor_map {
+    ($key:expr) => {
+        $key.signum();
+    };
+}
+
+fn main() {
+    cbor_map! { #[test(test)] 4};
+    //~^ ERROR removing an expression is not supported in this position
+    //~| ERROR attribute must be of the form `#[test]`
+    //~| WARNING this was previously accepted by the compiler but is being phased out
+}

tests/ui/macros/issue-111749.stderr

@@ -0,0 +1,18 @@
+error: removing an expression is not supported in this position
+  --> $DIR/issue-111749.rs:8:17
+   |
+LL |     cbor_map! { #[test(test)] 4};
+   |                 ^^^^^^^^^^^^^
+
+error: attribute must be of the form `#[test]`
+  --> $DIR/issue-111749.rs:8:17
+   |
+LL |     cbor_map! { #[test(test)] 4};
+   |                 ^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
+   = note: `#[deny(ill_formed_attribute_input)]` on by default
+
+error: aborting due to 2 previous errors
+