Add explicit fetch flag for 'bst pull' command

buildstream/_frontend/cli.py

@@ -431,8 +431,10 @@ def track(app, elements, deps, except_, cross_junctions):
               help="The URL of the remote cache (defaults to the first configured cache)")
 @click.argument('elements', nargs=-1,
                 type=click.Path(readable=False))
+@click.option('--fetch', 'fetch_', default=False, is_flag=True,
+              help="Enable auto-fetching of junction(s) automatically if element has dependencies")
 @click.pass_obj
-def pull(app, elements, deps, remote):
+def pull(app, elements, deps, remote, fetch_):
     """Pull a built artifact from the configured remote artifact cache.
 
     By default the artifact will be pulled one of the configured caches
@@ -446,7 +448,7 @@ def pull(app, elements, deps, remote):
         all:   All dependencies
     """
     with app.initialized(session_name="Pull"):
-        app.stream.pull(elements, selection=deps, remote=remote)
+        app.stream.pull(elements, selection=deps, remote=remote, fetch_subprojects=fetch_)
 
 
 ##################################################################

buildstream/_stream.py

@@ -289,13 +289,15 @@ class Stream():
     #    targets (list of str): Targets to pull
     #    selection (PipelineSelection): The selection mode for the specified targets
     #    remote (str): The URL of a specific remote server to pull from, or None
+    #    fetch_subprojects (bool): Flag to enable auto-fetch of junctions if they are needed by `targets`
     #
     # If `remote` specified as None, then regular configuration will be used
     # to determine where to pull artifacts from.
     #
     def pull(self, targets, *,
              selection=PipelineSelection.NONE,
-             remote=None):
+             remote=None,
+             fetch_subprojects):
 
         use_config = True
         if remote:
@@ -305,7 +307,7 @@ class Stream():
                                  selection=selection,
                                  use_artifact_config=use_config,
                                  artifact_remote_url=remote,
-                                 fetch_subprojects=True)
+                                 fetch_subprojects=fetch_subprojects)
 
         if not self._artifacts.has_fetch_remotes():
             raise StreamError("No artifact caches available for pulling artifacts")