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.

3 files changed, 29 insertions, 23 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
 
diff --git a/buildstream/types.py b/buildstream/types.py
index 7bc7a1664..3eb4a9110 100644
--- a/buildstream/types.py
+++ b/buildstream/types.py
@@ -48,6 +48,12 @@ class Scope(Enum):
     itself.
     """
 
+    NONE = 4
+    """Just the element itself, no dependencies.
+
+    *Since: 1.4*
+    """
+
 
 class Consistency():
     """Defines the various consistency states of a :class:`.Source`.
diff --git a/tests/frontend/buildcheckout.py b/tests/frontend/buildcheckout.py
index 1299fa190..d43bac863 100644
--- a/tests/frontend/buildcheckout.py
+++ b/tests/frontend/buildcheckout.py
@@ -90,9 +90,10 @@ def test_build_invalid_suffix_dep(datafiles, cli, strict, hardlinks):
 def test_build_checkout_deps(datafiles, cli, deps):
     project = os.path.join(datafiles.dirname, datafiles.basename)
     checkout = os.path.join(cli.directory, 'checkout')
+    element_name = "checkout-deps.bst"
 
     # First build it
-    result = cli.run(project=project, args=['build', 'target.bst'])
+    result = cli.run(project=project, args=['build', element_name])
     result.assert_success()
 
     # Assert that after a successful build, the builddir is empty
@@ -101,20 +102,15 @@ def test_build_checkout_deps(datafiles, cli, deps):
     assert not os.listdir(builddir)
 
     # Now check it out
-    result = cli.run(project=project, args=['checkout', 'target.bst', '--deps', deps, checkout])
+    result = cli.run(project=project, args=['checkout', element_name, '--deps', deps, checkout])
     result.assert_success()
 
-    # Check that the executable hello file is found in the checkout
-    filename = os.path.join(checkout, 'usr', 'bin', 'hello')
-
-    if deps == "run":
-        assert os.path.exists(filename)
-    else:
-        assert not os.path.exists(filename)
-
-    # Check that the executable hello file is found in the checkout
-    filename = os.path.join(checkout, 'usr', 'include', 'pony.h')
+    # Verify output of this element
+    filename = os.path.join(checkout, 'etc', 'buildstream', 'config')
+    assert os.path.exists(filename)
 
+    # Verify output of this element's runtime dependencies
+    filename = os.path.join(checkout, 'usr', 'bin', 'hello')
     if deps == "run":
         assert os.path.exists(filename)
     else: