Fix requirements.txt includes with relative paths

Fixes #28 and closes #29

src/flake8_requirements/checker.py

@@ -357,7 +357,7 @@ def discover_project_root_dir(cls):
             root_dir = os.path.abspath(os.path.join(root_dir, ".."))
 
     @classmethod
-    def resolve_requirement(cls, requirement, max_depth=0):
+    def resolve_requirement(cls, requirement, max_depth=0, path=None):
         """Resolves flags like -r in an individual requirement line."""
 
         option = None
@@ -377,10 +377,10 @@ def resolve_requirement(cls, requirement, max_depth=0):
                 raise RuntimeError(msg.format(requirement))
             resolved = []
             # Error out if requirements file cannot be opened.
-            with open(os.path.join(cls.root_dir, requirement)) as f:
+            with open(os.path.join(path or cls.root_dir, requirement)) as f:
                 for line in joinlines(f.readlines()):
                     resolved.extend(cls.resolve_requirement(
-                        line, max_depth - 1))
+                        line, max_depth - 1, os.path.dirname(f.name)))
             return resolved
 
         if option:

test/test_requirements.py

@@ -110,6 +110,26 @@ def test_resolve_requirement_with_file_recursion(self):
                 ["baz", "qux", "bar"],
             )
 
+    def test_resolve_requirement_with_relative_include(self):
+        with mock.patch(builtins_open, mock_open_multiple(files=OrderedDict((
+            ("requirements.txt", "-r requirements/production.txt"),
+            ("requirements/production.txt", "-r node/one.txt\nfoo"),
+            ("requirements/node/one.txt", "-r common.txt\n-r /abs/path.txt"),
+            ("requirements/node/common.txt", "bar"),
+            ("/abs/path.txt", "bis"),
+        )))) as m:
+            self.assertEqual(
+                Flake8Checker.resolve_requirement("-r requirements.txt", 5),
+                ["bar", "bis", "foo"],
+            )
+            m.assert_has_calls([
+                mock.call("requirements.txt"),
+                mock.call("requirements/production.txt"),
+                mock.call("requirements/node/one.txt"),
+                mock.call("requirements/node/common.txt"),
+                mock.call("/abs/path.txt"),
+            ])
+
     def test_init_with_no_requirements(self):
         with mock.patch(builtins_open, mock.mock_open()) as m:
             m.side_effect = IOError("No such file or directory"),