Stacked PRs with branches across forks

[chris-oo]

For most OSS projects including the ones I manage, branches don't live in the upstream repo and instead in forks that contributors submit as a PR back into the upstream repo. The FAQ mentions this isn't currently supported, but is this on the roadmap? I'm excited to use stacked PRs but unfortunately without this it's not very useful yet.

[liggitt]

+1, I was super-excited to try out the stacked workflow with something like etcd-io/etcd#21261, breaking that apart into a stack ... pushing to my personal fork worked great (https://github.com/liggitt/etcd/branches/all?query=protoc-stack&lastTab=overview), but it looks like the PR-opening doesn't yet work. Is the limitation only on the gh client side, and if so, is there a manual workaround to get the PRs opened to try out the server-side review workflows in the meantime?

When I tried submitting the stack just within my own fork anyway just to try out the PR flow, gh stack submit returned odd errors I'm not sure how to resolve

$ gh stack submit
? Multiple remotes found. Which remote should be used? origin
Pushing 13 branches to origin...
? Title for PR (branch protoc-stack/nil-safe): cleanup: use nil-safe getters
⚠ failed to create PR for protoc-stack/nil-safe: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between main and protoc-stack/nil-safe, Head ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/protocmp.Transform): test: use protocmp.Transform
⚠ failed to create PR for protoc-stack/protocmp.Transform: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/nil-safe and protoc-stack/protocmp.Transform, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/vet-errorf): vet: fix error message construction
⚠ failed to create PR for protoc-stack/vet-errorf: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/protocmp.Transform and protoc-stack/vet-errorf, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/messages-pointer): internal: pass messages by pointer
⚠ failed to create PR for protoc-stack/messages-pointer: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/vet-errorf and protoc-stack/messages-pointer, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/clone): internal: clone messages instead of shallow copy
⚠ failed to create PR for protoc-stack/clone: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/messages-pointer and protoc-stack/clone, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/mvccpb.Event): client: stop wrapping mvccpb.Event type
⚠ failed to create PR for protoc-stack/mvccpb.Event: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/clone and protoc-stack/mvccpb.Event, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/authpb.UserAddOptions): client: stop wrapping authpb.UserAddOptions type
⚠ failed to create PR for protoc-stack/authpb.UserAddOptions: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/mvccpb.Event and protoc-stack/authpb.UserAddOptions, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/client-pointers): client: stop passing proto by value
⚠ failed to create PR for protoc-stack/client-pointers: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/authpb.UserAddOptions and protoc-stack/client-pointers, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/client-Cmp-pointers): client: fix Cmp proto pass by value
⚠ failed to create PR for protoc-stack/client-Cmp-pointers: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/client-pointers and protoc-stack/client-Cmp-pointers, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/server-Snapshot-pointers): server: stop passing Snapshot by value
⚠ failed to create PR for protoc-stack/server-Snapshot-pointers: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/client-Cmp-pointers and protoc-stack/server-Snapshot-pointers, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/server-mvccpb.KeyValue-pointer): server: stop passing mvccpb.KeyValue by value
⚠ failed to create PR for protoc-stack/server-mvccpb.KeyValue-pointer: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/server-Snapshot-pointers and protoc-stack/server-mvccpb.KeyValue-pointer, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/etcdctl-pointers): etcdctl: stop passing proto by value
⚠ failed to create PR for protoc-stack/etcdctl-pointers: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/server-mvccpb.KeyValue-pointer and protoc-stack/etcdctl-pointers, Head ref must be a branch, Base ref must be a branch (createPullRequest)
? Title for PR (branch protoc-stack/drop-gogo): protoc stack/drop gogo
⚠ failed to create PR for protoc-stack/drop-gogo: creating PR: GraphQL: Head sha can't be blank, Base sha can't be blank, No commits between protoc-stack/etcdctl-pointers and protoc-stack/drop-gogo, Head ref must be a branch, Base ref must be a branch (createPullRequest)
✓ Pushed and synced 13 branches

[medmunds]

Is the limitation only on the gh client side, and if so, is there a manual workaround to get the PRs opened to try out the server-side review workflows in the meantime?

It seems to be a server-side limitation that "Cross-fork stacks are not supported."

I tried it with three PRs I already had open (that build on each other and would benefit from stacking). The cli was able to adopt the existing PRs, but it failed to submit the stack:

% gh stack init 37212-djangodocs-sphinx-ext-portability 35874-console-tabs-accessibility 37138-docs-sphinx-theme-pydata
✓ Adopted 3 branches: main ← 37212-djangodocs-sphinx-ext-portability ← 35874-console-tabs-accessibility ← 37138-docs-sphinx-theme-pydata
  You're on 37138-docs-sphinx-theme-pydata (top of stack).
  Found PRs for 3 of 3 branches.

% gh stack submit
Checking stack state...
Pushing to origin...
PR #21613 for 37212-djangodocs-sphinx-ext-portability is up to date
⚠ failed to update base branch for PR #21614: HTTP 422: Validation Failed (https://api.github.com/repos/django/django/pulls/21614)
PullRequest.base is invalid
⚠ failed to update base branch for PR #21586: HTTP 422: Validation Failed (https://api.github.com/repos/django/django/pulls/21586)
PullRequest.base is invalid
⚠ Stacked PRs are not enabled for this repository
✓ Pushed and synced 3 branches

The server-ops-only command gh stack link 21613 21614 21586 produces essentially the same error message.

("Stacked PRs are not enabled for this repository" seems to be complaining about my contributor fork, because stacked PRs are enabled for the upstream repo where the PRs are open.)

[medmunds]

… and the real limitation here seems to be that a PR's base branch must be in the PR's own repo. That's only true for the first PR in a contributor stack; later PRs are based on branches in the contributor's fork.

From elsewhere in the stack FAQ (emphasis added):

Stacked PRs on GitHub are based on the standard pull request model — any tool that creates PRs with the correct base branches can work with them.

So stacked PRs for OSS projects would need GitHub to support PRs with base branches in outside forks. Or allow the (read-only) refs/pull/… upstream mirror as a PR base branch. I'm guessing that's not on the roadmap anytime soon. (But we can hope 🤞)

[jglick]

To be explicit: it seems perfectly reasonable to require that all PR branches of a given stack live in the same repository—so long as it is permitted for this repository to be a fork of the repository hosting the base branch of the stack. If multiple contributors wish to collaborate on a complex stacked change, it is most straightforward to do so in an origin branch.

[jglick]

As a developer working on both OSS and proprietary repositories, I would note that this limitation could be a problem even for private (company-internal) repositories using an “inner source” model. As a product engineer I occasionally submit PRs from a personal fork to a documentation repository that I would certainly not expect to have write (and thus merge) permission to. Conversely, a sales architect should feel welcome to open a PR against a production code repository, to which the set of people with write permission is strictly limited. Admittedly PRs of this cross-team type are typically small and do not need sophisticated features like stacks, but not always.