[mypyc] Fix regression with nested functions (#16484)

Fixes #16480

Fix is straightforward, but also suspicious, since I am not sure how it
ever worked without this.

mypyc/irbuild/prebuildvisitor.py

@@ -119,9 +119,10 @@ def visit_decorator(self, dec: Decorator) -> None:
                 self.funcs_to_decorators[dec.func] = decorators_to_store
         super().visit_decorator(dec)
 
-    def visit_func_def(self, fdef: FuncItem) -> None:
+    def visit_func_def(self, fdef: FuncDef) -> None:
         # TODO: What about overloaded functions?
         self.visit_func(fdef)
+        self.visit_symbol_node(fdef)
 
     def visit_lambda_expr(self, expr: LambdaExpr) -> None:
         self.visit_func(expr)

mypyc/test-data/run-functions.test

@@ -1286,3 +1286,25 @@ def bar() -> None:
 bar()
 [out]
 {'__module__': 'native', '__name__': 'bar', '__qualname__': 'bar', '__doc__': None, '__wrapped__': <built-in function bar>}
+
+[case testCallNestedFunctionWithNamed]
+def f() -> None:
+    def a() -> None:
+        pass
+    def b() -> None:
+        a()
+    b()
+[file driver.py]
+from native import f
+f()
+
+[case testCallNestedFunctionWithLambda]
+def f(x: int) -> int:
+    def inc(x: int) -> int:
+        return x + 1
+    return (lambda x: inc(x))(1)
+[file driver.py]
+from native import f
+print(f(1))
+[out]
+2