Monomorphize generator field types for debuginfo

src/librustc_codegen_ssa/mir/mod.rs

@@ -627,6 +627,7 @@ fn arg_local_refs<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>(
                         .zip(state_tys)
                         .enumerate()
                         .filter_map(move |(i, (decl, ty))| {
+                            let ty = fx.monomorphize(&ty);
                             decl.name.map(|name| (i + upvar_count + 1, name, false, ty))
                         })
                 }).into_iter().flatten();

src/test/run-pass/generator/issue-58888.rs

@@ -0,0 +1,27 @@
+// run-pass
+// compile-flags: -g
+
+#![feature(generators, generator_trait)]
+
+use std::ops::Generator;
+
+struct Database;
+
+impl Database {
+    fn get_connection(&self) -> impl Iterator<Item = ()> {
+        Some(()).into_iter()
+    }
+
+    fn check_connection(&self) -> impl Generator<Yield = (), Return = ()> + '_ {
+        move || {
+            let iter = self.get_connection();
+            for i in iter {
+                yield i
+            }
+        }
+    }
+}
+
+fn main() {
+    Database.check_connection();
+}