_artifact.py: Do not create empty buildtree directories

Creating an empty buildtree directory when buildtree caching is disabled
means cached_buildtree() can return True even if no buildtree is
available, which breaks logic in the frontend and in Stream.

This adds the buildtree_exists() method to indicate whether an artifact
was created with a buildtree, independent of whether the buildtree is
available in the local cache.

1 files changed, 4 insertions, 4 deletions

diff --git a/tests/integration/shellbuildtrees.py b/tests/integration/shellbuildtrees.py
index 13d21548e..31af8a0e4 100644
--- a/tests/integration/shellbuildtrees.py
+++ b/tests/integration/shellbuildtrees.py
@@ -71,8 +71,8 @@ def test_buildtree_staged_warn_empty_cached(cli_integration, tmpdir, datafiles):
     res = cli_integration.run(project=project, args=[
         'shell', '--build', '--use-buildtree', 'always', element_name, '--', 'cat', 'test'
     ])
-    res.assert_shell_error()
-    assert "Artifact contains an empty buildtree" in res.stderr
+    res.assert_main_error(ErrorDomain.APP, None)
+    assert "Artifact was created without buildtree" in res.stderr
 
 
 @pytest.mark.datafiles(DATA_DIR)
@@ -148,8 +148,8 @@ def test_buildtree_from_failure_option_never(cli_integration, tmpdir, datafiles)
     res = cli_integration.run(project=project, args=[
         'shell', '--build', element_name, '--use-buildtree', 'always', '--', 'cat', 'test'
     ])
-    res.assert_shell_error()
-    assert "Artifact contains an empty buildtree" in res.stderr
+    res.assert_main_error(ErrorDomain.APP, None)
+    assert "Artifact was created without buildtree" in res.stderr
 
 
 @pytest.mark.datafiles(DATA_DIR)