[mypyc] Avoid crash when importing unknown module with from import (#…

…10550)

Fixes mypyc/mypyc#851

This fixes a bug where code compiled with mypyc would crash on from imports (from x import y) if:
 * y is a module
 * mypy doesn't know that y is a module (due to an ignore_missing_imports configuration option or something else)

The bug was caused by using getattr to import modules (i.e. y = getattr(x, 'y')) and changing this to import x.y as y when it can determine that y is a module. This doesn't work when we don't know that y is a module.

I changed the from import handling to use something similar to the method shown in the __import__ docs. I also removed the special casing of from imports for modules (from x import y where y is a module) mentioned earlier, because these changes make that special casing unnecessary.

mypyc/irbuild/builder.py

@@ -35,7 +35,7 @@
     SetAttr, LoadStatic, InitStatic, NAMESPACE_MODULE, RaiseStandardError
 )
 from mypyc.ir.rtypes import (
-    RType, RTuple, RInstance, int_rprimitive, dict_rprimitive,
+    RType, RTuple, RInstance, c_int_rprimitive, int_rprimitive, dict_rprimitive,
     none_rprimitive, is_none_rprimitive, object_rprimitive, is_object_rprimitive,
     str_rprimitive, is_tagged, is_list_rprimitive, is_tuple_rprimitive, c_pyssize_t_rprimitive
 )
@@ -45,7 +45,9 @@
 from mypyc.primitives.list_ops import to_list, list_pop_last, list_get_item_unsafe_op
 from mypyc.primitives.dict_ops import dict_get_item_op, dict_set_item_op
 from mypyc.primitives.generic_ops import py_setattr_op, iter_op, next_op
-from mypyc.primitives.misc_ops import import_op, check_unpack_count_op, get_module_dict_op
+from mypyc.primitives.misc_ops import (
+    import_op, check_unpack_count_op, get_module_dict_op, import_extra_args_op
+)
 from mypyc.crash import catch_errors
 from mypyc.options import CompilerOptions
 from mypyc.errors import Errors
@@ -286,19 +288,45 @@ def add_to_non_ext_dict(self, non_ext: NonExtClassInfo,
         key_unicode = self.load_str(key)
         self.call_c(dict_set_item_op, [non_ext.dict, key_unicode, val], line)
 
+    def gen_import_from(self, id: str, line: int, imported: List[str]) -> None:
+        self.imports[id] = None
+
+        globals_dict = self.load_globals_dict()
+        null = Integer(0, dict_rprimitive, line)
+        names_to_import = self.new_list_op([self.load_str(name) for name in imported], line)
+
+        level = Integer(0, c_int_rprimitive, line)
+        value = self.call_c(
+            import_extra_args_op,
+            [self.load_str(id), globals_dict, null, names_to_import, level],
+            line,
+        )
+        self.add(InitStatic(value, id, namespace=NAMESPACE_MODULE))
+
     def gen_import(self, id: str, line: int) -> None:
         self.imports[id] = None
 
         needs_import, out = BasicBlock(), BasicBlock()
-        first_load = self.load_module(id)
-        comparison = self.translate_is_op(first_load, self.none_object(), 'is not', line)
-        self.add_bool_branch(comparison, out, needs_import)
+        self.check_if_module_loaded(id, line, needs_import, out)
 
         self.activate_block(needs_import)
         value = self.call_c(import_op, [self.load_str(id)], line)
         self.add(InitStatic(value, id, namespace=NAMESPACE_MODULE))
         self.goto_and_activate(out)
 
+    def check_if_module_loaded(self, id: str, line: int,
+                               needs_import: BasicBlock, out: BasicBlock) -> None:
+        """Generate code that checks if the module `id` has been loaded yet.
+
+        Arguments:
+            id: name of module to check if imported
+            line: line number that the import occurs on
+            needs_import: the BasicBlock that is run if the module has not been loaded yet
+            out: the BasicBlock that is run if the module has already been loaded"""
+        first_load = self.load_module(id)
+        comparison = self.translate_is_op(first_load, self.none_object(), 'is not', line)
+        self.add_bool_branch(comparison, out, needs_import)
+
     def get_module(self, module: str, line: int) -> Value:
         # Python 3.7 has a nice 'PyImport_GetModule' function that we can't use :(
         mod_dict = self.call_c(get_module_dict_op, [], line)

mypyc/irbuild/statement.py

@@ -172,7 +172,8 @@ def transform_import_from(builder: IRBuilder, node: ImportFrom) -> None:
 
     id = importlib.util.resolve_name('.' * node.relative + node.id, module_package)
 
-    builder.gen_import(id, node.line)
+    imported = [name for name, _ in node.names]
+    builder.gen_import_from(id, node.line, imported)
     module = builder.load_module(id)
 
     # Copy everything into our module's dict.
@@ -181,12 +182,6 @@ def transform_import_from(builder: IRBuilder, node: ImportFrom) -> None:
     # This probably doesn't matter much and the code runs basically right.
     globals = builder.load_globals_dict()
     for name, maybe_as_name in node.names:
-        # If one of the things we are importing is a module,
-        # import it as a module also.
-        fullname = id + '.' + name
-        if fullname in builder.graph or fullname in module_state.suppressed:
-            builder.gen_import(fullname, node.line)
-
         as_name = maybe_as_name or name
         obj = builder.py_get_attr(module, name, node.line)
         builder.gen_method_call(

mypyc/primitives/misc_ops.py

@@ -3,7 +3,8 @@
 from mypyc.ir.ops import ERR_NEVER, ERR_MAGIC, ERR_FALSE
 from mypyc.ir.rtypes import (
     bool_rprimitive, object_rprimitive, str_rprimitive, object_pointer_rprimitive,
-    int_rprimitive, dict_rprimitive, c_int_rprimitive, bit_rprimitive, c_pyssize_t_rprimitive
+    int_rprimitive, dict_rprimitive, c_int_rprimitive, bit_rprimitive, c_pyssize_t_rprimitive,
+    list_rprimitive,
 )
 from mypyc.primitives.registry import (
     function_op, custom_op, load_address_op, ERR_NEG_INT
@@ -113,6 +114,15 @@
     c_function_name='PyImport_Import',
     error_kind=ERR_MAGIC)
 
+# Import with extra arguments (used in from import handling)
+import_extra_args_op = custom_op(
+    arg_types=[str_rprimitive, dict_rprimitive, dict_rprimitive,
+               list_rprimitive, c_int_rprimitive],
+    return_type=object_rprimitive,
+    c_function_name='PyImport_ImportModuleLevelObject',
+    error_kind=ERR_MAGIC
+)
+
 # Get the sys.modules dictionary
 get_module_dict_op = custom_op(
     arg_types=[],