plugins/elements/junction.py: Add 'ignore-junction-remotes' option

This option allows us to completely ignore remotes defined in the
subproject. As a user, we may not wish to interact with subproject
remotes as we may not be able to trust them, for example.

An appropriate test and some documentation has also been added.

3 files changed, 77 insertions, 4 deletions

diff --git a/src/buildstream/_project.py b/src/buildstream/_project.py
index 3a5923f80..dff101582 100644
--- a/src/buildstream/_project.py
+++ b/src/buildstream/_project.py
@@ -647,9 +647,13 @@ class Project():
 
         # If there is a junction Element which specifies that we want to remotely cache
         # its elements, append the junction's remotes to the artifact cache specs list
-        if self.junction and self.junction.cache_junction_elements:
+        if self.junction:
             parent = self.junction._get_project()
-            self.artifact_cache_specs = parent.artifact_cache_specs + self.artifact_cache_specs
+            if self.junction.cache_junction_elements:
+                self.artifact_cache_specs = parent.artifact_cache_specs + self.artifact_cache_specs
+
+            if self.junction.ignore_junction_remotes:
+                self.artifact_cache_specs = []
 
         # Load source caches with pull/push config
         self.source_cache_specs = SourceCache.specs_from_config_node(config, self.directory)
diff --git a/src/buildstream/plugins/elements/junction.py b/src/buildstream/plugins/elements/junction.py
index 235702b07..aec32516b 100644
--- a/src/buildstream/plugins/elements/junction.py
+++ b/src/buildstream/plugins/elements/junction.py
@@ -59,12 +59,18 @@ Overview
      # should interact with project remotes (default: False).
      cache-junction-elements: False
 
+     # Optionally ignore junction remotes, this means that BuildStream
+     # will not attempt to pull artifacts from the junction project's
+     # remote(s) (default: False).
+     ignore-junction-remotes: False
+
 .. note::
 
    The configuration option to allow specifying junction targets is available
    since :ref:`format version 24 <project_format_version>` and the configuration
-   option allowing junction project elements to interact with parent remotes is
-   available since :ref:`format version 25 <project_format_version>`.
+   options allowing for junction project elements to interact with parent remotes
+   or to completely ignore junction project remotes are available since
+   :ref:`format version 25 <project_format_version>`.
 
 .. note::
 
@@ -187,6 +193,7 @@ class JunctionElement(Element):
         self.target_element = None
         self.target_junction = None
         self.cache_junction_elements = node.get_bool('cache-junction-elements', default=False)
+        self.ignore_junction_remotes = node.get_bool('ignore-junction-remotes', default=False)
 
     def preflight(self):
         # "target" cannot be used in conjunction with:
diff --git a/tests/artifactcache/junctions.py b/tests/artifactcache/junctions.py
index bfddcedac..1fafb11f1 100644
--- a/tests/artifactcache/junctions.py
+++ b/tests/artifactcache/junctions.py
@@ -133,3 +133,65 @@ def test_caching_junction_elements(cli, tmpdir, datafiles):
         assert_not_shared(cli, base_share, project, 'target.bst', project_name='parent')
         assert_not_shared(cli, base_share, project, 'app.bst', project_name='parent')
         assert_shared(cli, base_share, base_project, 'base-element.bst', project_name='base')
+
+
+@pytest.mark.datafiles(DATA_DIR)
+def test_ignore_junction_remotes(cli, tmpdir, datafiles):
+    project = os.path.join(str(datafiles), 'parent')
+    base_project = os.path.join(str(project), 'base')
+
+    # Load the junction element
+    junction_element = os.path.join(project, 'base.bst')
+    junction_data = _yaml.roundtrip_load(junction_element)
+
+    with create_artifact_share(os.path.join(str(tmpdir), 'artifactshare-parent')) as share,\
+        create_artifact_share(os.path.join(str(tmpdir), 'artifactshare-base')) as base_share:
+
+        # Immediately declare the artifact caches in the appropriate project configs
+        project_set_artifacts(project, share.repo)
+        project_set_artifacts(base_project, base_share.repo)
+
+        # Build and populate the project remotes with their respective elements
+        result = cli.run(project=project, args=['build', 'target.bst'])
+        assert result.exit_code == 0
+
+        # And finally assert that the artifacts are in the right shares
+        #
+        # The parent project's cache should only contain project elements
+        assert_shared(cli, share, project, 'target.bst', project_name='parent')
+        assert_shared(cli, share, project, 'app.bst', project_name='parent')
+        assert_not_shared(cli, share, base_project, 'base-element.bst', project_name='base')
+
+        # The junction project's cache should only contain elements in the junction project
+        assert_not_shared(cli, base_share, project, 'target.bst', project_name='parent')
+        assert_not_shared(cli, base_share, project, 'app.bst', project_name='parent')
+        assert_shared(cli, base_share, base_project, 'base-element.bst', project_name='base')
+
+        # Ensure that, from now on, we ignore junction element remotes
+        junction_data['config'] = {"ignore-junction-remotes": True}
+        _yaml.roundtrip_dump(junction_data, junction_element)
+
+        # Now delete everything from the local cache and try to
+        # redownload from the shares.
+        #
+        cas = os.path.join(cli.directory, 'cas')
+        shutil.rmtree(cas)
+        artifact_dir = os.path.join(cli.directory, 'artifacts')
+        shutil.rmtree(artifact_dir)
+
+        # Assert that nothing is cached locally anymore
+        state = cli.get_element_state(project, 'target.bst')
+        assert state != 'cached'
+        state = cli.get_element_state(base_project, 'base-element.bst')
+        assert state != 'cached'
+
+        # Now try bst artifact pull
+        result = cli.run(project=project, args=['artifact', 'pull', '--deps', 'all', 'target.bst'])
+        assert result.exit_code == 0
+
+        # And assert that they are again in the local cache, without having built
+        state = cli.get_element_state(project, 'target.bst')
+        assert state == 'cached'
+        # We shouldn't be able to download base-element!
+        state = cli.get_element_state(base_project, 'base-element.bst')
+        assert state != 'cached'