[Bug]: Expanding unmodified lines in GitLab merge requests silently does nothing #17156

Activity

1. juliusmarminge commented on Oct 8, 2026

   

   juliusmarminge

   on Oct 8, 2026

   Member

   More actions

   Note

   Grok responding on behalf of Julius.

   Thanks for the clear report and the stack trace. I traced it on current main (5e22256). There are two separate problems here.

   1. The GitLab provider never wires up expansion

   The error comes from PullRequestService.diffFileContents (apps/server/src/pullRequest/PullRequestService.ts:1901-1923). It refuses with "This host cannot expand unchanged pull request lines." whenever the host's provider has no getDiffFileContents.

   GitLab can already do this read. GitLabPullRequestCli.getMergeRequestDiffFileContents (apps/server/src/pullRequest/GitLabPullRequestCli.ts:1250-1299) was added in #5546 and has tests (GitLabPullRequestCli.test.ts ~L620-780). It reads the MR's diff_refs (or a commit's parent for the per-commit view). Then it fetches both sides from projects/:id/repository/files/:path/raw?ref=<sha>, with the same 1 MB and binary limits as GitHub.

   The step that's missing is in GitLabPullRequestProvider.ts. GitHub wires its CLI method into the provider (GitHubPullRequestProvider.ts:549-550), and Forgejo and Azure DevOps have their own. The GitLab provider only exposes getDiff (GitLabPullRequestProvider.ts:231) and never sets getDiffFileContents. So the optional method is undefined, it's left out at PullRequestService.ts:643-645, and every expand on a GitLab MR fails. The provider file at #5546's merge commit has the same gap, so this looks like an oversight from that PR rather than a later regression.

   The fix is likely small. Add the following to the GitLab provider, next to getDiff, plus a provider-level test:

   getDiffFileContents: (input) =>
     cli.getMergeRequestDiffFileContents(input).pipe(Effect.mapError(fail("getDiffFileContents"))),

   I haven't run this against a live GitLab instance. Fork MRs and older self-managed GitLab (see #15660 / #15886) are worth a quick check once it's wired.

   Bitbucket appears to be in the same state: diff: true but no getDiffFileContents. It probably fails the same way, though I didn't verify that.

   2. The web UI swallows the failure

   Even with GitLab fixed, any expansion failure is currently invisible. That includes the existing "oversized" (>1 MB) and "binary" errors on GitHub.

   • The Code tab passes createPullRequestDiffFileContentsLoader to the diff viewer as loadDiffFiles (apps/web/src/components/pullRequest/PullRequestCodeTab.tsx:361-371, 896). The loader throws on failure (apps/web/src/lib/diffFileContents.ts:119-121).
   • useAtomCommand's default failure reporting only does a console.warn (packages/client-runtime/src/state/runtime.ts:418-433). It doesn't show a toast.
   • @pierre/diffs 1.5.2 FileDiff.loadFilesForDiff catches the loader error and just calls console.error (dist/components/FileDiff.js:555-563). That's the trace in your report. expandHunk likely still re-renders, but with nothing loaded to reveal, so the click appears to do nothing.

   There's also no capability flag for expansion: PullRequestCapabilities (packages/contracts/src/pullRequest.ts:394) only has diff. So the client can't hide or disable the "N unmodified lines" divider for a host that can't expand. How to surface this is a UX choice: show an error toast or inline notice when the loader fails, add an expand capability and hide the divider, or both. Fixing (1) removes the GitLab case either way.

   Summary

   • Type: bug. GitLab expansion was meant to ship with feat: expand pull request review context and panel tabs #5546, but the provider wiring was missed. A secondary issue is the silent-failure UX in the PR Code tab.
   • Related: feat: expand pull request review context and panel tabs #5546 (added the feature), [Bug]: Pull request Code tab fails on self-managed GitLab older than 15.7 ("GitLab CLI command failed") #15660 / fix(server): load merge request diffs on older GitLab #15886 (different GitLab Code tab bug on older self-managed GitLab), [Bug]: Side-by-side diff squeezes the "N unmodified lines" divider into the line-number column #17157 (same reporter, cosmetic split-diff divider). I didn't find an open PR that fixes this.
   • Next step: wire getDiffFileContents into GitLabPullRequestProvider with a test, and separately decide how expansion failures should be shown in the Code tab.
2. juliusmarminge

   added

   bugSomething is broken or behaving incorrectly.Something is broken or behaving incorrectly.

   via-triageFiled through npx t3 triageFiled through npx t3 triage

   on Oct 8, 2026