Relative imports should work even if they are not within the project

jedi/inference/imports.py

@@ -245,7 +245,38 @@ class Importer:
         )
 
     def follow(self):
-        if not self.import_path or not self._infer_possible:
+        if not self.import_path:
+            if self._fixed_sys_path:
+                # This is a bit of a special case, that maybe should be
+                # revisited. If the project path is wrong or the user uses
+                # relative imports the wrong way, we might end up here, where
+                # the `fixed_sys_path == project.path` in that case we kind of
+                # use the project.path.parent directory as our path. This is
+                # usually not a problem, except if imorts in other places are
+                # using the same names. Example:
+                #
+                # foo/                       < #1
+                #   - setup.py
+                #   - foo/                   < #2
+                #     - __init__.py
+                #     - foo.py               < #3
+                #
+                # If the top foo is our project folder and somebody uses
+                # `from . import foo` in `setup.py`, it will resolve to foo #2,
+                # which means that the import for foo.foo is cached as
+                # `__init__.py` (#2) and not as `foo.py` (#3). This is usually
+                # not an issue, because this case is probably pretty rare, but
+                # might be an issue for some people.
+                from jedi.inference.value.namespace import ImplicitNamespaceValue
+                import_path = (os.path.basename(self._fixed_sys_path[0]),)
+                ns = ImplicitNamespaceValue(
+                    self._inference_state,
+                    string_names=import_path,
+                    paths=self._fixed_sys_path,
+                )
+                return ValueSet({ns})
+            return NO_VALUES
+        if not self._infer_possible:
             return NO_VALUES
 
         # Check caches first

test/test_api/test_usages.py

@@ -3,7 +3,7 @@ import pytest
 
 def test_import_references(Script):
     s = Script("from .. import foo", path="foo.py")
-    assert [usage.line for usage in s.get_references(line=1, column=18)] == [1]
+    assert [usage.line for usage in s.get_references()] == [1]
 
 
 def test_exclude_builtin_modules(Script):

test/test_inference/test_imports.py

@@ -8,6 +8,7 @@ from pathlib import Path
 
 import pytest
 
+import jedi
 from jedi.file_io import FileIO
 from jedi.inference import compiled
 from jedi.inference import imports
@@ -468,3 +469,23 @@ def test_relative_import_star(Script):
     script = Script(source, path='export.py')
 
     assert script.complete(3, len("furl.c"))
+
+
+@pytest.mark.parametrize('with_init', [False, True])
+def test_relative_imports_without_path_and_setup_py(
+        Script, inference_state, environment, tmpdir, with_init):
+    # Contrary to other tests here we create a temporary folder that is not
+    # part of a folder with a setup py that signifies
+    tmpdir.join('file1.py').write('do_foo = 1')
+    other_path = tmpdir.join('other_files')
+    other_path.join('file2.py').write('def do_nothing():\n pass', ensure=True)
+    if with_init:
+        other_path.join('__init__.py').write('')
+
+    for name, code in [('file2', 'from . import file2'),
+                       ('file1', 'from .. import file1')]:
+        for func in (jedi.Script.goto, jedi.Script.infer):
+            n, = func(Script(code, path=other_path.join('test1.py').strpath))
+            assert n.name == name
+            assert n.type == 'module'
+            assert n.line == 1