Urgh I made some wrong amends and I'm too tired to separate the commits out this time

ancestor: Split out of reachability
mergebase: Add merge base routines
internal/commitquery: Add commit query context engine thingy
internal/peel: Shared tag peeling
errors: Shared object query errors
internal/testgit: Add rooted repo helpers; remove raw path access
objectstore/memory: Add in-memory object store
objectid: Add Compare helper

1 files changed, 5 insertions, 0 deletions

diff --git a/internal/commitquery/errors.go b/internal/commitquery/errors.go
new file mode 100644
index 00000000..e99011d0
--- /dev/null
+++ b/internal/commitquery/errors.go
@@ -0,0 +1,5 @@
+package commitquery
+
+import "errors"
+
+var errBadGenerationOrder = errors.New("commitquery: priority queue violated generation ordering")