Ensure `--deps=none` option works for `bst checkout`

Currently, `bst checkout --deps none` command always produces empty
output. Fix this issue and add regression test for the same.

- element_enums.py: Add Scope.NONE.

- element.py: Ensure Scope.NONE works correctly in addition to
  Scope.RUN/Scope.ALL in Element.dependencies() and Element.search().

- tests/frontend/buildcheckout.py: Fix tests for `--deps none`.

Fixes #670.

1 files changed, 15 insertions, 11 deletions

diff --git a/buildstream/element.py b/buildstream/element.py
index d7072dc8c..d94f2e8ad 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -438,7 +438,7 @@ class Element(Plugin):
                                                 visited=visited, recursed=True)
 
         # Yeild self only at the end, after anything needed has been traversed
-        if should_yield and (recurse or recursed) and (scope in (Scope.ALL, Scope.RUN)):
+        if should_yield and (recurse or recursed) and scope != Scope.BUILD:
             yield self
 
     def search(self, scope, name):
@@ -1353,17 +1353,21 @@ class Element(Plugin):
                 if scope == Scope.BUILD:
                     self.stage(sandbox)
                 elif scope == Scope.RUN:
-                    # Stage deps in the sandbox root
                     if deps == 'run':
-                        with self.timed_activity("Staging dependencies", silent_nested=True):
-                            self.stage_dependency_artifacts(sandbox, scope)
-
-                        # Run any integration commands provided by the dependencies
-                        # once they are all staged and ready
-                        if integrate:
-                            with self.timed_activity("Integrating sandbox"):
-                                for dep in self.dependencies(scope):
-                                    dep.integrate(sandbox)
+                        dependency_scope = Scope.RUN
+                    else:
+                        dependency_scope = Scope.NONE
+
+                    # Stage deps in the sandbox root
+                    with self.timed_activity("Staging dependencies", silent_nested=True):
+                        self.stage_dependency_artifacts(sandbox, dependency_scope)
+
+                    # Run any integration commands provided by the dependencies
+                    # once they are all staged and ready
+                    if integrate:
+                        with self.timed_activity("Integrating sandbox"):
+                            for dep in self.dependencies(dependency_scope):
+                                dep.integrate(sandbox)
 
             yield sandbox