Merge commit '7819677343bb40e899fa2cd252c203013911fede'

3 files changed, 56 insertions, 1 deletions

diff --git a/morphlib/plugins/branch_and_merge_new_plugin.py b/morphlib/plugins/branch_and_merge_new_plugin.py
index 5a33d47b..e09417d2 100644
--- a/morphlib/plugins/branch_and_merge_new_plugin.py
+++ b/morphlib/plugins/branch_and_merge_new_plugin.py
@@ -15,6 +15,7 @@
 
 
 import cliapp
+import glob
 import logging
 import os
 import shutil
@@ -22,6 +23,13 @@ import shutil
 import morphlib
 
 
+class BranchRootHasNoSystemsError(cliapp.AppException):
+    def __init__(self, repo, ref):
+        cliapp.AppException.__init__(
+            self, 'System branch root repository %s '
+                  'has no system morphologies at ref %s' % (repo, ref))
+
+
 class SimpleBranchAndMergePlugin(cliapp.Plugin):
 
     '''Add subcommands for handling workspaces and system branches.'''
@@ -131,6 +139,10 @@ class SimpleBranchAndMergePlugin(cliapp.Plugin):
 
             gd = sb.clone_cached_repo(
                 cached_repo, system_branch, system_branch)
+
+            if not self._checkout_has_systems(gd):
+                raise BranchRootHasNoSystemsError(root_url, system_branch)
+
             gd.update_submodules(self.app)
             gd.update_remotes()
         except BaseException as e:
@@ -202,6 +214,10 @@ class SimpleBranchAndMergePlugin(cliapp.Plugin):
             gd = sb.clone_cached_repo(cached_repo, system_branch, base_ref)
             gd.branch(system_branch, base_ref)
             gd.checkout(system_branch)
+
+            if not self._checkout_has_systems(gd):
+                raise BranchRootHasNoSystemsError(root_url, base_ref)
+
             gd.update_submodules(self.app)
             gd.update_remotes()
         except BaseException as e:
@@ -267,3 +283,12 @@ class SimpleBranchAndMergePlugin(cliapp.Plugin):
                 msg="WARNING: %(message)s",
                 message=str(e), error=True)
 
+    @staticmethod
+    def _checkout_has_systems(gd):
+        for filename in glob.iglob(os.path.join(gd.dirname, '*.morph')):
+            with open(filename) as mf:
+                morphology = morphlib.morph2.Morphology(mf.read())
+                if morphology['kind'] == 'system':
+                    return True
+        return False
+
diff --git a/yarns/branches-workspaces.yarn b/yarns/branches-workspaces.yarn
index bfcb9e66..3af362a1 100644
--- a/yarns/branches-workspaces.yarn
+++ b/yarns/branches-workspaces.yarn
@@ -58,6 +58,15 @@ Checking out a system branch should fail, if the branch doesn't exist.
     WHEN        morph attempts to check out system branch foo
     THEN        morph failed
 
+Checking out a system branch should also fail if the repository does
+not contain any system morphologies.
+
+    SCENARIO    checking out a system branch with no systems
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        morph attempts to check out a repository with no systems
+    THEN        morph failed
+
 We can, instead, create a new system branch, off master.
 
     SCENARIO    branch off master
@@ -78,6 +87,15 @@ to check for that locally.
     AND         creating system branch bar, based on foo
     THEN        the system branch bar is checked out
 
+Similarly, attempting to branch a system branch should fail if the
+repository does not contain any system morphologies.
+
+    SCENARIO    checking out a system branch with no systems
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        morph attempts to branch a repository with no systems
+    THEN        morph failed
+
 Query commands in workspaces
 ----------------------------
 
diff --git a/yarns/implementations.yarn b/yarns/implementations.yarn
index 6c0ef6e2..7f9281ac 100644
--- a/yarns/implementations.yarn
+++ b/yarns/implementations.yarn
@@ -124,7 +124,13 @@ Attempt to check out a system branch, and remember if it failed.
 
     IMPLEMENTS WHEN morph attempts to check out system branch (\S+)
     cd "$DATADIR/workspace"
-    attempt_morph checkout "$MATCH_1"
+    attempt_morph checkout test:morphs "$MATCH_1"
+
+Attempt to check out a system branch from a root that has no systems.
+
+    IMPLEMENTS WHEN morph attempts to check out a repository with no systems
+    cd "$DATADIR/workspace"
+    attempt_morph checkout test:test-chunk master
 
 We also need to verify that a system branch has been checked out.
 
@@ -145,6 +151,12 @@ We can create a new branch, off another system branch.
     cd "$DATADIR/workspace"
     run_morph branch test:morphs "$MATCH_1" "$MATCH_2"
 
+Attempt to branch a system branch from a root that had no systems.
+
+    IMPLEMENTS WHEN morph attempts to branch a repository with no systems
+    cd "$DATADIR/workspace"
+    attempt_morph branch test:test-chunk foo
+
 Pushing all changes in a system branch checkout to the git server.
 
     IMPLEMENTS WHEN pushing system branch (\S+) to git server