A stab at davidhalter/jedi#361 (Flask extension imports)

Both new-style and old-style extensions work, but only when imported
with a 'from'.  There are two skipped tests of the full dotted name
imports.

Also, our fixture has a normal flaskext package, whereas in practice
the flaskext module is injected from a pth file and does not have
__init__.py, we need to figure out to handle that.

jedi/evaluate/imports.py

@@ -343,6 +343,25 @@ class _Importer(object):
 
     @memoize_default(NO_DEFAULT)
     def follow_file_system(self):
+        # Handle "magic" Flask extension imports:
+        # ``flask.ext.foo`` is really ``flask_foo`` or ``flaskext.foo``.
+        if [part._string for part in self.import_path[:2]] == ['flask', 'ext']:
+            orig_path = tuple(self.import_path)
+            part = orig_path[2]
+            pos = (part._line, part._column)
+            try:
+                self.import_path = (
+                    pr.NamePart('flask_' + part._string, part.parent, pos),
+                ) + orig_path[3:]
+                return self._real_follow_file_system()
+            except ModuleNotFound as e:
+                self.import_path = (
+                    pr.NamePart('flaskext', part.parent, pos),
+                ) + orig_path[2:]
+                return self._real_follow_file_system()
+        return self._real_follow_file_system()
+
+    def _real_follow_file_system(self):
         if self.file_path:
             sys_path_mod = list(self.sys_path_with_modifications())
             if not self.module.has_explicit_absolute_import:

test/test_evaluate/flask-site-packages/flask_baz/__init__.py

@@ -0,0 +1 @@
+Baz = 1

test/test_evaluate/flask-site-packages/flask_foo.py

@@ -0,0 +1,2 @@
+class Foo(object):
+    pass

test/test_evaluate/flask-site-packages/flaskext/bar.py

@@ -0,0 +1,2 @@
+class Bar(object):
+    pass

test/test_evaluate/flask-site-packages/flaskext/moo/__init__.py

@@ -0,0 +1 @@
+Moo = 1

test/test_evaluate/test_imports.py

@@ -1,3 +1,6 @@
+import os
+import sys
+
 import pytest
 
 import jedi
@@ -23,3 +26,36 @@ def test_import_not_in_sys_path():
     assert a[0].name == 'str'
     a = jedi.Script(path='module.py', line=7).goto_definitions()
     assert a[0].name == 'str'
+
+
+def setup_function(function):
+    sys.path.append(os.path.join(
+        os.path.dirname(__file__), 'flask-site-packages'))
+
+
+def teardown_function(function):
+    path = os.path.join(os.path.dirname(__file__), 'flask-site-packages')
+    sys.path.remove(path)
+
+
+@pytest.mark.parametrize("script,name", [
+    ("from flask.ext import foo; foo.", "Foo"), # flask_foo.py
+    ("from flask.ext import bar; bar.", "Bar"), # flaskext/bar.py
+    ("from flask.ext import baz; baz.", "Baz"), # flask_baz/__init__.py
+    ("from flask.ext import moo; moo.", "Moo"), # flaskext/moo/__init__.py
+])
+def test_flask_ext(script, name):
+    """flask.ext.foo is really imported from flaskext.foo or flask_foo.
+    """
+    assert name in [c.name for c in jedi.Script(script).completions()]
+
+
+@pytest.mark.xfail
+@pytest.mark.parametrize("script,name", [
+    ("import flask.ext.foo; flask.ext.foo.", "Foo"),
+    ("import flask.ext.bar; flask.ext.bar.", "Foo"),
+    ("import flask.ext.baz; flask.ext.baz.", "Foo"),
+    ("import flask.ext.moo; flask.ext.moo.", "Foo"),
+])
+def test_flask_ext_more(script, name):
+    assert name in [c.name for c in jedi.Script(script).completions()]