py/compile: Disallow 'import *' outside module level.

This check follows CPython's behaviour, because 'import *' always populates
the globals with the imported names, not locals.

Since it's safe to do this (doesn't lead to a crash or undefined behaviour)
the check is only enabled for MICROPY_CPYTHON_COMPAT.

Fixes issue #5121.

py/compile.c

@@ -1196,6 +1196,13 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
     } while (0);
 
     if (MP_PARSE_NODE_IS_TOKEN_KIND(pns->nodes[1], MP_TOKEN_OP_STAR)) {
+        #if MICROPY_CPYTHON_COMPAT
+        if (comp->scope_cur->kind != SCOPE_MODULE) {
+            compile_syntax_error(comp, (mp_parse_node_t)pns, "import * not at module level");
+            return;
+        }
+        #endif
+
         EMIT_ARG(load_const_small_int, import_level);
 
         // build the "fromlist" tuple

tests/cmdline/cmd_showbc.py

@@ -115,7 +115,7 @@ def f():
     # import
     import a
     from a import b
-    from a import *
+    #from sys import * # tested at module scope
 
     # raise
     raise
@@ -154,3 +154,6 @@ del Class
 # load super method
 def f(self):
     super().f()
+
+# import * (needs to be in module scope)
+from sys import *

tests/cmdline/cmd_showbc.py.exp

@@ -7,7 +7,7 @@ arg names:
 (N_EXC_STACK 0)
   bc=0 line=1
 ########
-  bc=\\d\+ line=155
+  bc=\\d\+ line=159
 00 MAKE_FUNCTION \.\+
 \\d\+ STORE_NAME f
 \\d\+ MAKE_FUNCTION \.\+
@@ -27,6 +27,11 @@ arg names:
 \\d\+ DELETE_NAME Class
 \\d\+ MAKE_FUNCTION \.\+
 \\d\+ STORE_NAME f
+\\d\+ LOAD_CONST_SMALL_INT 0
+\\d\+ LOAD_CONST_STRING '*'
+\\d\+ BUILD_TUPLE 1
+\\d\+ IMPORT_NAME 'sys'
+\\d\+ IMPORT_STAR
 \\d\+ LOAD_CONST_NONE
 \\d\+ RETURN_VALUE
 File cmdline/cmd_showbc.py, code block 'f' (descriptor: \.\+, bytecode @\.\+ bytes)
@@ -300,11 +305,6 @@ Raw bytecode (code_info_size=\\d\+, bytecode_size=\\d\+):
 \\d\+ IMPORT_FROM 'b'
 \\d\+ STORE_DEREF 14
 \\d\+ POP_TOP
-\\d\+ LOAD_CONST_SMALL_INT 0
-\\d\+ LOAD_CONST_STRING '*'
-\\d\+ BUILD_TUPLE 1
-\\d\+ IMPORT_NAME 'a'
-\\d\+ IMPORT_STAR
 \\d\+ RAISE_LAST
 \\d\+ LOAD_CONST_SMALL_INT 1
 \\d\+ RAISE_OBJ

tests/import/import_star_error.py

@@ -0,0 +1,13 @@
+# test errors with import *
+
+# 'import *' is not allowed in function scope
+try:
+    exec('def foo(): from x import *')
+except SyntaxError as er:
+    print('function', 'SyntaxError')
+
+# 'import *' is not allowed in class scope
+try:
+    exec('class C: from x import *')
+except SyntaxError as er:
+    print('class', 'SyntaxError')