repository: Deprecate `SetConfig()` RPC

With the `SetConfig()` RPC, we used to allow Rails to modify the on-disk
config of a Git repository. As a result, we have on-disk state that is
hard to observe for Gitaly and which can lead to hard-to-debug issues
when the config contains unexpected entries. We have thus worked towards
the goal of having complete control over the gitconfig in Gitaly:

    - Users of on-disk remotes now use in-memory ones.

    - JWT tokens are passed via header fields in requests which fetch
      objects from a remote repository, where the token is injected via
      environment variables.

    - The last valid usecase of modifying the gitconfig is to set
      "gitlab.fullpath". This usecase has since grown its own RPC call
      `SetFullPath()`.

As a result, we don't have any users left which call either
`SetConfig()` or `DeleteConfig()`. This commit thus marks both as
deprecated so we can remove them in the next release.

Changelog: deprecation

1 files changed, 10 insertions, 0 deletions

diff --git a/proto/repository-service.proto b/proto/repository-service.proto
index 3e8f11338..bc4b6f245 100644
--- a/proto/repository-service.proto
+++ b/proto/repository-service.proto
@@ -142,13 +142,23 @@ service RepositoryService {
     };
   }
 
+  // SetConfig writes a set of config entries into the target repository's
+  // gitconfig. This RPC is deprecated with no general replacement: modifying
+  // the on-disk gitconfig is not supported anymore. The only usecase that is
+  // still supported is writing "gitlab.fullpath" via the new `SetFullPath()`
+  // RPC.
   rpc SetConfig(SetConfigRequest) returns (SetConfigResponse) {
+    option deprecated = true;
     option (op_type) = {
       op: MUTATOR
     };
   }
 
+  // DeleteConfig deletes a set of config entries from the target repository's
+  // gitconfig. This RPC is deprecated with no replacement: modifying the
+  // on-disk gitconfig is not supported anymore.
   rpc DeleteConfig(DeleteConfigRequest) returns (DeleteConfigResponse) {
+    option deprecated = true;
     option (op_type) = {
       op: MUTATOR
     };