Fix a goto_assignments issue with a better internal API

Fixes #996.

jedi/api/__init__.py

@@ -212,9 +212,7 @@ class Script(object):
 
         if follow_imports:
             def check(name):
-                if isinstance(name, ModuleName):
+                return name.is_import()
-                    return False
-                return name.api_type == 'module'
         else:
             def check(name):
                 return isinstance(name, imports.SubModuleName)

jedi/evaluate/filters.py

@@ -42,6 +42,9 @@ class AbstractNameDefinition(object):
     def execute_evaluated(self, *args, **kwargs):
         return self.infer().execute_evaluated(*args, **kwargs)
 
+    def is_import(self):
+        return False
+
     @property
     def api_type(self):
         return self.parent_context.api_type
@@ -55,6 +58,10 @@ class AbstractTreeName(AbstractNameDefinition):
     def goto(self):
         return self.parent_context.evaluator.goto(self.parent_context, self.tree_name)
 
+    def is_import(self):
+        imp = search_ancestor(self.tree_name, 'import_from', 'import_name')
+        return imp is not None
+
     @property
     def string_name(self):
         return self.tree_name.value

test/test_evaluate/test_imports.py

@@ -199,6 +199,11 @@ def test_goto_following_on_imports(Script):
     assert (g[0].line, g[0].column) != (0, 0)
 
 
+def test_goto_assignments(Script):
+    sys, = Script("import sys", 1, 10).goto_assignments(follow_imports=True)
+    assert sys.type == 'module'
+
+
 def test_os_after_from(Script):
     def check(source, result, column=None):
         completions = Script(source, column=column).completions()