Improve error when local HEAD of definitions repo is not found in remote

Old error:

    ERROR: Git directory
    /build/cache/gits/git___git_baserock_org_baserock_baserock_definitions
    has no commit at ref 5046c3a0e4fd587c23f7c6a9e0d0b50d1914dcca^{commit}.

New error:

    ERROR: Commit 5046c3a0e4fd587c23f7c6a9e0d0b50d1914dcca wasn't found
    in the "origin" remote
    git://git.baserock.org/baserock/baserock/definitions. You either need
    to push your local commits on branch xxx to "origin", or use the
    --local-changes=include feature.

Change-Id: I0c3658e9cd27c23f40653662ba7e4ba58b7892de

3 files changed, 30 insertions, 7 deletions

diff --git a/morphlib/definitions_repo.py b/morphlib/definitions_repo.py
index 66cdb31c..40aeecff 100644
--- a/morphlib/definitions_repo.py
+++ b/morphlib/definitions_repo.py
@@ -216,10 +216,17 @@ class DefinitionsRepo(gitdir.GitDirectory):
             if status_cb:
                 status_cb(msg='Deciding on task order')
 
-            yield morphlib.sourceresolver.create_source_pool(
-                lrc, rrc, repo_url, commit, [system_filename],
-                cachedir=cachedir, original_ref=ref, update_repos=update_repos,
-                status_cb=status_cb)
+            try:
+                yield morphlib.sourceresolver.create_source_pool(
+                    lrc, rrc, repo_url, commit, [system_filename],
+                    cachedir=cachedir, original_ref=ref,
+                    update_repos=update_repos, status_cb=status_cb)
+            except morphlib.sourceresolver.InvalidDefinitionsRefError as e:
+                raise cliapp.AppException(
+                    'Commit %s wasn\'t found in the "origin" remote %s. '
+                    'You either need to push your local commits on branch %s '
+                    'to "origin", or use the --local-changes=include feature '
+                    'of Morph.' % (e.ref, e.repo_url, ref))
 
     def load_all_morphologies(self, loader):
         mf = morphlib.morphologyfinder.MorphologyFinder(self)
diff --git a/morphlib/sourceresolver.py b/morphlib/sourceresolver.py
index c1e68db7..47d9502e 100644
--- a/morphlib/sourceresolver.py
+++ b/morphlib/sourceresolver.py
@@ -122,6 +122,18 @@ class InvalidVersionFileError(SourceResolverError): #pragma: no cover
         SourceResolverError.__init__(self, "invalid VERSION file")
 
 
+# Callers may want to give the user a special error message if we hit an
+# InvalidRefError in the definitions.git repo. Currently a separate exception
+# type seems the easiest way to do that, but adding enough detail to the
+# gitdir.InvalidRefError class may make this class redundant in future.
+class InvalidDefinitionsRefError(SourceResolverError):  # pragma: no cover
+    def __init__(self, repo_url, ref):
+        self.repo_url = repo_url
+        self.ref = ref
+        super(InvalidDefinitionsRefError, self).__init__(
+            "Ref %s was not found in repo %s." % (ref, repo_url))
+
+
 class SourceResolver(object):
     '''Provides a way of resolving the set of sources for a given system.
 
@@ -580,8 +592,12 @@ class SourceResolver(object):
              self.buildsystem_cache_manager.open() as resolved_buildsystems:
 
             # Resolve the repo, ref pair for definitions repo, cache result
-            definitions_absref, definitions_tree = self._resolve_ref(
-                resolved_trees, definitions_repo, definitions_ref)
+            try:
+                definitions_absref, definitions_tree = self._resolve_ref(
+                    resolved_trees, definitions_repo, definitions_ref)
+            except morphlib.gitdir.InvalidRefError as e:
+                raise InvalidDefinitionsRefError(
+                    definitions_repo, definitions_ref)
 
             if definitions_original_ref:
                 definitions_ref = definitions_original_ref
diff --git a/tests.build/missing-ref.stderr b/tests.build/missing-ref.stderr
index b5139e25..ac730554 100644
--- a/tests.build/missing-ref.stderr
+++ b/tests.build/missing-ref.stderr
@@ -1 +1 @@
-ERROR: Git directory TMP/morphs-repo has no commit at ref non-existent-branch^{commit}.
+ERROR: Ref non-existent-branch was not found in repo test:morphs-repo.