py/builtinimport: Remove unreachable code for relative imports.

The while-loop that calls chop_component will guarantee that level==-1 at
the end of the loop.  Hence the code following it is unnecessary.

The check for p==this_name will catch imports that are beyond the
top-level, and also covers the case of new_mod_q==MP_QSTR_ (equivalent to
new_mod_l==0) so that check is removed.

There is also a new check at the start for level>=0 to guard against
__import__ being called with bad level values.

1 files changed, 6 insertions, 21 deletions

diff --git a/py/builtinimport.c b/py/builtinimport.c
index 173e040afb..5142c7d8f5 100644
--- a/py/builtinimport.c
+++ b/py/builtinimport.c
@@ -261,6 +261,9 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
         fromtuple = args[3];
         if (n_args >= 5) {
             level = MP_OBJ_SMALL_INT_VALUE(args[4]);
+            if (level < 0) {
+                mp_raise_ValueError(NULL);
+            }
         }
     }
 
@@ -305,28 +308,13 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
             chop_component(this_name, &p);
         }
 
-
-        uint dots_seen = 0;
         while (level--) {
             chop_component(this_name, &p);
-            dots_seen++;
         }
 
-        if (dots_seen == 0 && level >= 1) {
-            // http://legacy.python.org/dev/peps/pep-0328/#relative-imports-and-name
-            // "If the module's name does not contain any package information
-            // (e.g. it is set to '__main__') then relative imports are
-            // resolved as if the module were a top level module, regardless
-            // of where the module is actually located on the file system."
-            // Supposedly this if catches this condition and resolve it properly
-            // TODO: But nobody knows for sure. This condition happens when
-            // package's __init__.py does something like "import .submod". So,
-            // maybe we should check for package here? But quote above doesn't
-            // talk about packages, it talks about dot-less module names.
-            DEBUG_printf("Warning: no dots in current module name and level>0\n");
-            p = this_name + this_name_l;
-        } else if (level != -1) {
-            mp_raise_msg(&mp_type_ImportError, "invalid relative import");
+        // We must have some component left over to import from
+        if (p == this_name) {
+            mp_raise_ValueError("cannot perform relative import");
         }
 
         uint new_mod_l = (mod_len == 0 ? (size_t)(p - this_name) : (size_t)(p - this_name) + 1 + mod_len);
@@ -339,9 +327,6 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
 
         qstr new_mod_q = qstr_from_strn(new_mod, new_mod_l);
         DEBUG_printf("Resolved base name for relative import: '%s'\n", qstr_str(new_mod_q));
-        if (new_mod_q == MP_QSTR_) {
-            mp_raise_ValueError("cannot perform relative import");
-        }
         module_name = MP_OBJ_NEW_QSTR(new_mod_q);
         mod_str = new_mod;
         mod_len = new_mod_l;