proto: Add structured error types for UserSquash RPC

We're about to introduce support for structured errors in the UserSquash
RPC. We cannot roll out this change even with a feature flag though
because some of our testing infrastructure will always test code with
all feature flags enabled. We thus have to land the protobuf changes
independently such that we can adjust downstream callers.

This commit introduces these changes by creating a new UserSquashError
Protobuf message which contains all potential structured errors we want
to return from the UserSquash RPC.

Changelog: added

1 files changed, 16 insertions, 0 deletions

diff --git a/proto/errors.proto b/proto/errors.proto
index 241c2cb90..8e0b2298b 100644
--- a/proto/errors.proto
+++ b/proto/errors.proto
@@ -17,6 +17,15 @@ message AccessCheckError {
   bytes changes = 4;
 }
 
+// MergeConflictError is an error returned in the case when merging two commits
+// fails due to a merge conflict.
+message MergeConflictError {
+  // ConflictingFiles is the set of files which have been conflicting. If this
+  // field is empty, then there has still been a merge conflict, but it wasn't
+  // able to determine which files have been conflicting.
+  repeated bytes conflicting_files = 1;
+}
+
 // ReferenceUpdateError is an error returned when updating a reference has
 // failed.
 message ReferenceUpdateError {
@@ -27,3 +36,10 @@ message ReferenceUpdateError {
   // NewOid is the object ID the reference should have pointed to after the update.
   string new_oid = 3;
 }
+
+// ResolveRevisionError is an error returned when resolving a specific revision
+// has failed.
+message ResolveRevisionError {
+  // Revision is the name of the revision that was tried to be resolved.
+  bytes revision = 1;
+}