Auto merge of #16684 - Veykril:synthetic-fmt-args, r=Veykril

fix: Don't panic on synthetic syntax in inference diagnostics

Temporary fix for https://github.com/rust-lang/rust-analyzer/issues/16682

We ought to rethink how we attach diagnostics to things, as IDs don't work for `format_args` like that!

crates/ide-diagnostics/src/handlers/unresolved_ident.rs

@@ -20,6 +20,19 @@ pub(crate) fn unresolved_ident(
 mod tests {
     use crate::tests::check_diagnostics;
 
+    // FIXME: This should show a diagnostic
+    #[test]
+    fn feature() {
+        check_diagnostics(
+            r#"
+//- minicore: fmt
+fn main() {
+    format_args!("{unresolved}");
+}
+"#,
+        )
+    }
+
     #[test]
     fn missing() {
         check_diagnostics(