proto: Introduce FindTagError to distinguish non-existent tagspks-find-tag-error

When the FindTag RPC is invoked with a tag that doesn't exist then we
return an `Internal` gRPC error. This is clearly not ideal given that
those errors count against our SLOs, and furthermore it's an expected
error condition to say that a tag does not exist. We should thus slap on
a proper error code in that condition.

This raises an issue in the Rails codebase though because the `NotFound`
code is typically used to indicate a missing repository. So if we now
also start to retrun `NotFound` for missing tags then it's hard for
Rails to distinguish those two error conditions without matching the
error's message.

To fix this issue we introduce a structured error that gives the caller
a clear indication that the reference was indeed not found so that they
can distinguish those two conditions.

2 files changed, 8 insertions, 0 deletions

diff --git a/ruby/proto/gitaly/errors_pb.rb b/ruby/proto/gitaly/errors_pb.rb
index 620b645e5..f772b7291 100644
--- a/ruby/proto/gitaly/errors_pb.rb
+++ b/ruby/proto/gitaly/errors_pb.rb
@@ -31,6 +31,9 @@ Google::Protobuf::DescriptorPool.generated_pool.build do
       optional :reference_name, :bytes, 1
       optional :oid, :string, 2
     end
+    add_message "gitaly.ReferenceNotFoundError" do
+      optional :reference_name, :bytes, 1
+    end
     add_message "gitaly.ReferenceUpdateError" do
       optional :reference_name, :bytes, 1
       optional :old_oid, :string, 2
@@ -65,6 +68,7 @@ module Gitaly
   MergeConflictError = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.MergeConflictError").msgclass
   ReferencesLockedError = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.ReferencesLockedError").msgclass
   ReferenceExistsError = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.ReferenceExistsError").msgclass
+  ReferenceNotFoundError = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.ReferenceNotFoundError").msgclass
   ReferenceUpdateError = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.ReferenceUpdateError").msgclass
   ResolveRevisionError = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.ResolveRevisionError").msgclass
   LimitError = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.LimitError").msgclass
diff --git a/ruby/proto/gitaly/ref_pb.rb b/ruby/proto/gitaly/ref_pb.rb
index bfd341832..72aa78039 100644
--- a/ruby/proto/gitaly/ref_pb.rb
+++ b/ruby/proto/gitaly/ref_pb.rb
@@ -73,6 +73,9 @@ Google::Protobuf::DescriptorPool.generated_pool.build do
     add_message "gitaly.FindTagResponse" do
       optional :tag, :message, 1, "gitaly.Tag"
     end
+    add_message "gitaly.FindTagError" do
+      optional :tag_not_found, :message, 1, "gitaly.ReferenceNotFoundError"
+    end
     add_message "gitaly.FindAllTagsRequest" do
       optional :repository, :message, 1, "gitaly.Repository"
       optional :sort_by, :message, 2, "gitaly.FindAllTagsRequest.SortBy"
@@ -239,6 +242,7 @@ module Gitaly
   FindAllBranchesResponse::Branch = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.FindAllBranchesResponse.Branch").msgclass
   FindTagRequest = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.FindTagRequest").msgclass
   FindTagResponse = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.FindTagResponse").msgclass
+  FindTagError = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.FindTagError").msgclass
   FindAllTagsRequest = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.FindAllTagsRequest").msgclass
   FindAllTagsRequest::SortBy = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.FindAllTagsRequest.SortBy").msgclass
   FindAllTagsRequest::SortBy::Key = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.FindAllTagsRequest.SortBy.Key").enummodule