Add 'dir' as a valid step attribute (#853)

Add 'dir' attribute for steps, as well as tests for it. Corresponding tests added as well.

fixes #847

docs/sections/cli_features.md

@@ -66,6 +66,7 @@ steps:
 - id: mystep
   uses: docker://ubuntu:18.04
   runs: ["ls", "-l"]
+  dir: /tmp/
   env:
     MYENVVAR: "foo"
 ```

docs/sections/cn_workflows.md

@@ -43,7 +43,7 @@ step. All attributes are optional with the exception of the `uses` attribute.
 | `env`       | **optional** The environment variables to set inside the container's runtime environment. If<br>you need to pass environment variables into a step, make sure it runs a command<br>shell to perform variable substitution. For example, if your `runs` attribute is<br>set to `["sh", "-c"]`, the value of `args` will be passed to `sh -c` and<br>executed in a command shell. Alternatively, if your `Dockerfile` uses an<br>`ENTRYPOINT` to run the same command (`"sh -c"`), `args` will execute in a<br>command shell as well. See [`ENTRYPOINT`](https://docs.docker.com/engine/reference/builder/#entrypoint) for more details. |
 | `secrets`   | **optional** Specifies the names of the secret variables to set in the runtime environment<br>which the container can access as an environment variable. For example,<br>`secrets: ["SECRET1", "SECRET2"]`. |
 | `skip_pull` | **optional** Assume that the given container image already exist and skip pulling it. |
-
+| `dir`       | **optional** Specifies the working directory for a step. By default, the directory is always `/workspace` if another one is not defined. |
 ### Referencing images in a step
 
 A step in a workflow can reference a container image defined in a 
@@ -211,7 +211,27 @@ popper run -f /home/user/proj/wf.yml -w /home/user/proj/
 
 The above writes the `/home/user/proj/myfile` even though Popper is 
 being invoked from `/tmp`, since the `-w` flag is being passed to 
-`ppopper run`.
+`popper run`.
+
+### Changing the working directory
+
+To specify a working directory for a step you can use the `dir` attribute
+in the workflow. This going to change where the specified
+command is executed.
+
+For example, adding `dir` to a workflow results in the following:
+
+```yaml
+version: '1'
+steps:
+- uses: docker://alpine:3.9
+  args: [touch, ./myfile]
+  dir: /path/to/dir/
+```
+
+It is worth mentioning that if the directory is specified outside the
+`/workspace` folder, then anything that gets written to it won't persist
+(see below for more).
 
 ### Filesystem namespaces and persistence
 

src/popper/parser.py

@@ -28,6 +28,7 @@ class WorkflowParser(object):
                             "args": {"type": "seq", "sequence": [{"type": "str"}]},
                             "runs": {"type": "seq", "sequence": [{"type": "str"}]},
                             "secrets": {"type": "seq", "sequence": [{"type": "str"}]},
+                            "dir": {"type": "str"},
                             "skip_pull": {"type": "bool"},
                             "env": {
                                 "type": "map",

src/popper/runner_host.py

@@ -248,7 +248,7 @@ def _get_container_kwargs(self, step, img, name):
                 f"{self._config.workspace_dir}:/workspace",
                 "/var/run/docker.sock:/var/run/docker.sock",
             ],
-            "working_dir": "/workspace",
+            "working_dir": step.dir if step.dir else "/workspace",
             "environment": self._prepare_environment(step),
             "entrypoint": step.runs if step.runs else None,
             "detach": not self._config.pty,

src/test/test_parser.py

@@ -31,7 +31,13 @@ def test_new_workflow(self):
 
         wf_data = {
             "steps": [
-                {"uses": "foo", "id": "step", "env": {"EN": "EE"}, "secrets": ["S"]},
+                {
+                    "uses": "foo",
+                    "id": "step",
+                    "env": {"EN": "EE"},
+                    "secrets": ["S"],
+                    "dir": "/path/to/",
+                },
                 {"uses": "bar", "runs": ["a", "b"], "args": ["c"], "skip_pull": True},
             ],
             "options": {"env": {"FOO": "bar"}, "secrets": ["Z"]},
@@ -43,6 +49,7 @@ def test_new_workflow(self):
         self.assertEqual("foo", step.uses)
         self.assertEqual(("Z", "S"), step.secrets)
         self.assertEqual({"EN": "EE", "FOO": "bar"}, step.env)
+        self.assertEqual("/path/to/", step.dir)
         self.assertTrue(not step.runs)
         self.assertTrue(not step.args)
         self.assertFalse(step.skip_pull)
@@ -52,9 +59,9 @@ def test_new_workflow(self):
         self.assertEqual(("a", "b"), step.runs)
         self.assertEqual(("c",), step.args)
         self.assertTrue(step.skip_pull)
+        self.assertTrue(not step.dir)
         self.assertEqual({"FOO": "bar"}, step.env)
         self.assertEqual(("Z",), step.secrets)
-
         self.assertEqual({"FOO": "bar"}, wf.options.env)
         self.assertEqual(("Z",), wf.options.secrets)
 

src/test/test_runner_host.py

@@ -141,7 +141,12 @@ def test_stop_running_tasks(self):
     @unittest.skipIf(os.environ.get("ENGINE", "docker") != "docker", "ENGINE != docker")
     def test_get_container_kwargs(self):
         step = Box(
-            {"uses": "popperized/bin/sh@master", "args": ["ls"], "id": "one",},
+            {
+                "uses": "popperized/bin/sh@master",
+                "args": ["ls"],
+                "id": "one",
+                "dir": "/tmp/",
+            },
             default_box=True,
         )
 
@@ -176,7 +181,7 @@ def test_get_container_kwargs(self):
                         "/var/run/docker.sock:/var/run/docker.sock",
                         "/path/in/host:/path/in/container",
                     ],
-                    "working_dir": "/workspace",
+                    "working_dir": "/tmp/",
                     "environment": {"FOO": "bar"},
                     "entrypoint": None,
                     "detach": True,
@@ -207,7 +212,7 @@ def test_get_container_kwargs(self):
                         "/var/run/docker.sock:/var/run/docker.sock",
                         "/path/in/host:/path/in/container",
                     ],
-                    "working_dir": "/workspace",
+                    "working_dir": "/tmp/",
                     "environment": {"FOO": "bar"},
                     "entrypoint": None,
                     "detach": False,