Add Error to git track if track and ref are not present

This is to address #471 that
documented unhelpfull behavour when tracking git sources.

It is a back port of
!580 and
!628

buildstream/_pipeline.py

@@ -358,10 +358,15 @@ class Pipeline():
                     inconsistent.append(element)
 
         if inconsistent:
-            detail = "Exact versions are missing for the following elements\n" + \
-                     "Try tracking these elements first with `bst track`\n\n"
+            detail = "Exact versions are missing for the following elements:\n\n"
+
             for element in inconsistent:
-                detail += "  " + element._get_full_name() + "\n"
+                detail += "  " + element._get_full_name()
+                for source in element.sources():
+                    if not source._get_consistency() and not source.get_ref():
+                        detail += ": Source {} is missing ref\n".format(source)
+            detail += "\nTry tracking these elements first with `bst track`\n"
+
             raise PipelineError("Inconsistent pipeline", detail=detail, reason="inconsistent-pipeline")
 
     #############################################################

buildstream/plugins/sources/git.py

@@ -80,6 +80,7 @@ from configparser import RawConfigParser
 
 from buildstream import Source, SourceError, Consistency, SourceFetcher
 from buildstream import utils
+from buildstream._exceptions import LoadError, LoadErrorReason
 
 GIT_MODULES = '.gitmodules'
 
@@ -296,6 +297,12 @@ class GitSource(Source):
         self.original_url = self.node_get_member(node, str, 'url')
         self.mirror = GitMirror(self, '', self.original_url, ref)
         self.tracking = self.node_get_member(node, str, 'track', None)
+
+        # At this point we now know if the source has a ref and/or a track.
+        # If it is missing both then we will be unable to track or build.
+        if self.mirror.ref is None and self.tracking is None:
+            raise LoadError(LoadErrorReason.INVALID_DATA, "{}: Git sources require a ref and/or track".format(self))
+
         self.checkout_submodules = self.node_get_member(node, bool, 'checkout-submodules', True)
         self.submodules = []
 
@@ -359,6 +366,12 @@ class GitSource(Source):
 
         # If self.tracking is not specified it's not an error, just silently return
         if not self.tracking:
+            # Is there a better way to check if a ref is given.
+            if self.mirror.ref is None:
+                detail = 'Without a tracking branch ref can not be updated. Please ' + \
+                         'provide a ref or a track.'
+                raise SourceError("{}: No track or ref".format(self),
+                                  detail=detail, reason="track-attempt-no-track")
             return None
 
         with self.timed_activity("Tracking {} from {}"

tests/sources/git.py

 import os
 import pytest
 
-from buildstream._exceptions import ErrorDomain
+from buildstream._exceptions import ErrorDomain, LoadErrorReason
 from buildstream import _yaml
 
 from tests.testutils import cli, create_repo
@@ -359,3 +359,41 @@ def test_submodule_track_ignore_inconsistent(cli, tmpdir, datafiles):
 
     # Assert that we are just fine without it, and emit a warning to the user.
     assert "Ignoring inconsistent submodule" in result.stderr
+
+
+@pytest.mark.skipif(HAVE_GIT is False, reason="git is not available")
+@pytest.mark.datafiles(os.path.join(DATA_DIR, 'template'))
+def test_submodule_track_no_ref_or_track(cli, tmpdir, datafiles):
+    project = os.path.join(datafiles.dirname, datafiles.basename)
+
+    # Create the repo from 'repofiles' subdir
+    repo = create_repo('git', str(tmpdir))
+    ref = repo.create(os.path.join(project, 'repofiles'))
+
+    # Write out our test target
+    gitsource = repo.source_config(ref=None)
+    gitsource.pop('track')
+    element = {
+        'kind': 'import',
+        'sources': [
+            gitsource
+        ]
+    }
+
+    _yaml.dump(element, os.path.join(project, 'target.bst'))
+
+    # Track will encounter an inconsistent submodule without any ref
+    result = cli.run(project=project, args=['track', 'target.bst'])
+    result.assert_main_error(ErrorDomain.LOAD, LoadErrorReason.INVALID_DATA)
+    result.assert_task_error(None, None)
+
+    # Assert that we are just fine without it, and emit a warning to the user.
+    assert "Git sources require a ref and/or track" in result.stderr
+
+    # Track will encounter an inconsistent submodule without any ref
+    result = cli.run(project=project, args=['build', 'target.bst'])
+    result.assert_main_error(ErrorDomain.LOAD, LoadErrorReason.INVALID_DATA)
+    result.assert_task_error(None, None)
+
+    # Assert that we are just fine without it, and emit a warning to the user.
+    assert "Git sources require a ref and/or track" in result.stderr