py/compile: Refine SyntaxError for repeated use of global/nonlocal.

py/compile.c

@@ -1355,9 +1355,8 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
 STATIC void compile_declare_global(compiler_t *comp, mp_parse_node_t pn, qstr qst) {
     bool added;
     id_info_t *id_info = scope_find_or_add_id(comp->scope_cur, qst, &added);
-    if (!added) {
-        // TODO this is not compliant with CPython
-        compile_syntax_error(comp, pn, "identifier already used");
+    if (!added && id_info->kind != ID_INFO_KIND_GLOBAL_EXPLICIT) {
+        compile_syntax_error(comp, pn, "identifier redefined as global");
         return;
     }
     id_info->kind = ID_INFO_KIND_GLOBAL_EXPLICIT;
@@ -1382,9 +1381,8 @@ STATIC void compile_global_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
 STATIC void compile_declare_nonlocal(compiler_t *comp, mp_parse_node_t pn, qstr qst) {
     bool added;
     id_info_t *id_info = scope_find_or_add_id(comp->scope_cur, qst, &added);
-    if (!added) {
-        // TODO this is not compliant with CPython
-        compile_syntax_error(comp, pn, "identifier already used");
+    if (!added && id_info->kind != ID_INFO_KIND_FREE) {
+        compile_syntax_error(comp, pn, "identifier redefined as nonlocal");
         return;
     }
     id_info_t *id_info2 = scope_find_local_in_parent(comp->scope_cur, qst);

tests/basics/scope.py

+# test scoping rules
+
+# explicit global variable
+a = 1
+def f():
+    global a
+    global a, a # should be able to redefine as global
+    a = 2
+f()
+print(a)
+
+# explicit nonlocal variable
+def f():
+    a = 1
+    def g():
+        nonlocal a
+        nonlocal a, a # should be able to redefine as nonlocal
+        a = 2
+    g()
+    return a
+print(f())

tests/basics/syntaxerror.py

@@ -77,8 +77,7 @@ test_syntax("return")
 test_syntax("yield")
 test_syntax("nonlocal a")
 
-# errors on uPy but shouldn't
-#test_syntax("global a; global a")
+# error on uPy, warning on CPy
 #test_syntax("def f():\n a = 1\n global a")
 
 # default except must be last
@@ -109,3 +108,12 @@ test_syntax("def f(a, a): pass")
 
 # nonlocal must exist in outer function/class scope
 test_syntax("def f():\n def g():\n  nonlocal a")
+
+# param can't be redefined as global
+test_syntax('def f(x):\n global x')
+
+# param can't be redefined as nonlocal
+test_syntax('def f(x):\n nonlocal x')
+
+# can define variable to be both nonlocal and global
+test_syntax('def f():\n nonlocal x\n global x')