Add a scheduled workflow to synchronize Git GUI's branches

[dscho]

To support contributors wishing to contribute to Git GUI via a mail-based flow, GitGitGadget maps Git GUI's branches into the git-gui/ namespace. For example, Git GUI's master branch is synchronized to https://github.com/gitgitgadget/git as git-gui/master and can be targeted via PRs.

To keep those git-gui/* branches synchronized, GitGitGadget has https://dev.azure.com/gitgitgadget/git/_build/index?definitionId=10

As part of the initiative to move away from Azure Pipelines, this commit offers a reimplementation of that Azure Pipeline as a GitHub workflow.

This workflow was verified to work correctly by temporarily adding a push trigger: https://github.com/gitgitgadget/gitgitgadget-workflows/actions/runs/5910229339/job/16031599392

[webstech]

@dscho, waiting for changes in PR #2 to be mirrored here.

[dscho]

@dscho, waiting for changes in PR #2 to be mirrored here.

@webstech thank you for reminding me that I forgot to do this yet. Here is the range-diff:

• 1: a855e8d ! 1: eddbced Add a scheduled workflow to synchronize Git GUI's branches

  @@ .github/workflows/sync-git-gui.yml (new)
   +  TARGET_REPOSITORY: gitgitgadget/git
   +  TARGET_REF_NAMESPACE: git-gui/
   +
  -+# Ideally, we would want to limit queuing to a single workflow run (i.e. if
  -+# there is already an active workflow run and a queued one, don't queue another
  -+# one), but that's not supported.
  ++# We want to limit queuing to a single workflow run i.e. if there is already
  ++# an active workflow run and a queued one, queue another one canceling the
  ++# already queued one.
   +concurrency:
   +  group: ${{ github.workflow }}
   +
  @@ .github/workflows/sync-git-gui.yml (new)
   +            }
   +
   +            const getRefs = async (repository, stripRefsPrefix) => {
  -+              for (let i = 1; i <= 10; i++) {
  ++              let attemptCounter = 1
  ++              for (;;) {
   +                try {
   +                  const [owner, repo] = repository.split('/')
   +                  let { data } = await github.rest.git.listMatchingRefs({
  @@ .github/workflows/sync-git-gui.yml (new)
   +                  if (e?.status !== 502) throw e
   +                }
   +
  -+                const seconds = i * i + 15 * Math.random()
  ++                if (++attemptCounter > 10) throw new Error('Giving up listing refs after 10 attempts')
  ++
  ++                const seconds = attemptCounter * attemptCounter + 15 * Math.random()
   +                core.info(`Encountered a Server Error; retrying in ${seconds} seconds`)
   +                await sleep(1000 * seconds)
   +              }
  @@ .github/workflows/sync-git-gui.yml (new)
   +            const refspecs = []
   +            const toFetch = new Set()
   +            for (let i = 0, j = 0; i < sourceRefs.length || j < targetRefs.length; ) {
  -+              const c =  i >= sourceRefs.length
  ++              const compare = i >= sourceRefs.length
   +                ? +1
   +                : j >= targetRefs.length
   +                  ? -1
   +                  : sourceRefs[i].name.localeCompare(targetRefs[j].name)
  -+              if (c > 0) {
  ++              if (compare > 0) {
   +                // no source ref => delete target ref
  -+                refspecs.push(`:${targetPrefix}${targetRefs[j++].name}`)
  -+              } else if (c < 0) {
  ++                refspecs.push(`:${targetPrefix}${targetRefs[j].name}`)
  ++                j++
  ++              } else if (compare < 0) {
   +                // no corresponding target ref yet => push source ref (new)
   +                const sha = sourceRefs[i].object.sha
   +                toFetch.add(sha)
  -+                refspecs.push(`${sha}:${targetPrefix}${sourceRefs[i++].name}`)
  -+              } else if (c === 0 && sourceRefs[i].object.sha !== targetRefs[j].object.sha) {
  -+                // target ref needs updating
  -+                const sha = sourceRefs[i].object.sha
  -+                toFetch.add(sha)
  -+                refspecs.push(`+${sha}:${targetPrefix}${sourceRefs[i++].name}`)
  -+                j++
  ++                refspecs.push(`${sha}:${targetPrefix}${sourceRefs[i].name}`)
  ++                i++
   +              } else {
  ++                // the sourceRef's name matches the targetRef's
  ++                if (sourceRefs[i].object.sha !== targetRefs[j].object.sha) {
  ++                  // target ref needs updating
  ++                  const sha = sourceRefs[i].object.sha
  ++                  toFetch.add(sha)
  ++                  refspecs.push(`+${sha}:${targetPrefix}${sourceRefs[i].name}`)
  ++                }
   +                i++
   +                j++
   +              }

[webstech]

Thanks!