py/builtinimport: Support relative import in custom __import__ callback.

The globals need to be forwarded from the caller's context.

Signed-off-by: Damien George <damien@micropython.org>

tests/import/builtin_import.py

@@ -20,3 +20,12 @@ try:
     __import__("xyz", None, None, None, -1)
 except ValueError:
     print("ValueError")
+
+# globals is not checked for level=0
+__import__("builtins", "globals")
+
+# globals must be a dict (or None) for level>0
+try:
+    __import__("builtins", "globals", None, None, 1)
+except TypeError:
+    print("TypeError")

tests/import/import_override2.py

@@ -0,0 +1,18 @@
+# test overriding __import__ combined with importing from the filesystem
+
+
+def custom_import(name, globals, locals, fromlist, level):
+    if level > 0:
+        print("import", name, fromlist, level)
+    return orig_import(name, globals, locals, fromlist, level)
+
+
+orig_import = __import__
+try:
+    __import__("builtins").__import__ = custom_import
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
+# import calls __import__ behind the scenes
+import pkg7.subpkg1.subpkg2.mod3