_stream/cli: Add pull option to shell

This will fetch artifacts if they're not local or are incomplete.

Part of #1044

1 files changed, 13 insertions, 5 deletions

diff --git a/src/buildstream/_stream.py b/src/buildstream/_stream.py
index 6f6d30f17..8097f451d 100644
--- a/src/buildstream/_stream.py
+++ b/src/buildstream/_stream.py
@@ -140,6 +140,7 @@ class Stream():
     #    isolate (bool): Whether to isolate the environment like we do in builds
     #    command (list): An argv to launch in the sandbox, or None
     #    usebuildtree (str): Whether to use a buildtree as the source, given cli option
+    #    pull_dependencies ([Element]|None): Elements to attempt to pull
     #
     # Returns:
     #    (int): The exit code of the launched shell
@@ -149,20 +150,27 @@ class Stream():
               mounts=None,
               isolate=False,
               command=None,
-              usebuildtree=None):
+              usebuildtree=None,
+              pull_dependencies=None):
 
         # Assert we have everything we need built, unless the directory is specified
         # in which case we just blindly trust the directory, using the element
         # definitions to control the execution environment only.
         if directory is None:
             missing_deps = [
-                dep._get_full_name()
-                for dep in self._pipeline.dependencies([element], scope)
+                dep for dep in self._pipeline.dependencies([element], scope)
                 if not dep._cached()
             ]
             if missing_deps:
-                raise StreamError("Elements need to be built or downloaded before staging a shell environment",
-                                  detail="\n".join(missing_deps))
+                if not pull_dependencies:
+                    raise StreamError(
+                        "Elements need to be built or downloaded before staging a shell environment",
+                        detail="\n"
+                        .join(list(map(lambda x: x._get_full_name(), missing_deps))))
+                self._message(MessageType.INFO, "Attempting to fetch missing or incomplete artifacts")
+                self._add_queue(PullQueue(self._scheduler))
+                self._enqueue_plan([element] + missing_deps)
+                self._run()
 
         buildtree = False
         # Check if we require a pull queue attempt, with given artifact state and context