Download run-time dependencies when running a target remotely (#3453)

The code path taken when `plz run`ning a binary target is slightly
different for remote execution vs local execution - ensure the target's
transitive run-time dependencies are all downloaded by the client before
it runs the target.

Author: chrisnovakovic

src/remote/remote.go

@@ -351,10 +351,13 @@ func (c *Client) Build(target *core.BuildTarget) (*core.BuildMetadata, error) {
 		if err := c.Download(target); err != nil {
 			return metadata, err
 		}
-		// TODO(peterebden): Should this not just be part of Download()?
+		// TODO(peterebden): Should these not just be part of Download()?
 		if err := c.downloadData(target); err != nil {
 			return metadata, err
 		}
+		if err := c.downloadRuntimeDependencies(target); err != nil {
+			return metadata, err
+		}
 	}
 	return metadata, nil
 }
@@ -376,6 +379,22 @@ func (c *Client) downloadData(target *core.BuildTarget) error {
 	return g.Wait()
 }
 
+// downloadRuntimeDependencies downloads all the runtime dependencies for a target.
+func (c *Client) downloadRuntimeDependencies(target *core.BuildTarget) error {
+	var g errgroup.Group
+	for runDep := range target.IterAllRuntimeDependencies(c.state.Graph) {
+		l, _ := runDep.Label()
+		t := c.state.Graph.TargetOrDie(l)
+		g.Go(func() error {
+			if err := c.Download(t); err != nil {
+				return err
+			}
+			return nil
+		})
+	}
+	return g.Wait()
+}
+
 // Run runs a target on the remote executors.
 func (c *Client) Run(target *core.BuildTarget) error {
 	if err := c.CheckInitialised(); err != nil {