dvc: reproduce stage if it has no dependencies and has cmd

This allows as to define conditional stages in the dependency graph.

Fixes #646
Fixes #648

Signed-off-by: Ruslan Kuprieiev <[email protected]>

dvc/stage.py

@@ -92,6 +92,10 @@ class Stage(object):
 
     def changed(self):
         ret = False
+
+        if not self.is_data_source and len(self.deps) == 0:
+            ret = True
+
         for entry in itertools.chain(self.outs, self.deps):
             if entry.changed():
                 ret = True

tests/test_repro.py

@@ -28,6 +28,22 @@ class TestRepro(TestDvc):
                      cmd='python {} {} {}'.format(self.CODE, self.FOO, self.file1))
 
 
+class TestReproNoDeps(TestRepro):
+    def test(self):
+        out = 'out'
+        code_file = 'out.py'
+        stage_file = 'out.dvc'
+        code = 'import uuid\nwith open("{}", "w+") as fd:\n\tfd.write(str(uuid.uuid4()))\n'.format(out)
+        with open(code_file, 'w+') as fd:
+            fd.write(code)
+        self.dvc.run(fname=stage_file,
+                     outs=[out],
+                     cmd='python {}'.format(code_file))
+
+        stages = self.dvc.reproduce(stage_file)
+        self.assertEqual(len(stages), 1)
+
+
 class TestReproForce(TestRepro):
     def test(self):
         stages = self.dvc.reproduce(self.file1_stage, force=True)