fix(gitlab): fetch merge request heads using GitLab refs

apps/server/src/git/GitManager.test.ts

@@ -5607,6 +5607,58 @@ it.layer(layerGitManagerTest)("GitManager", (it) => {
     }),
   );
 
+  it.effect("materializes and refreshes GitLab worktrees without source repository metadata", () =>
+    Effect.gen(function* () {
+      const repoDir = yield* makeTempDir("t3code-git-manager-");
+      yield* initRepo(repoDir);
+      const remoteDir = yield* createBareRemote();
+      yield* runGit(repoDir, ["remote", "add", "origin", remoteDir]);
+      yield* runGit(repoDir, ["push", "-u", "origin", "main"]);
+      yield* runGit(repoDir, ["checkout", "-b", "author"]);
+      NodeFS.writeFileSync(NodePath.join(repoDir, "mr.txt"), "first head\n");
+      yield* runGit(repoDir, ["add", "mr.txt"]);
+      yield* runGit(repoDir, ["commit", "-m", "First MR head"]);
+      yield* runGit(repoDir, ["push", "origin", "HEAD:refs/merge-requests/90/head"]);
+      const firstHead = (yield* runGit(repoDir, ["rev-parse", "HEAD"])).stdout.trim();
+      yield* runGit(repoDir, ["checkout", "main"]);
+
+      const provider = yield* GitLabSourceControlProvider.make.pipe(
+        Effect.provide(
+          Layer.mock(GitLabCli.GitLabCli)({
+            getMergeRequest: () =>
+              Effect.succeed({
+                number: 90,
+                title: "Fork MR",
+                url: "https://gitlab.com/group/project/-/merge_requests/90",
+                baseRefName: "main",
+                headRefName: "feature/mr",
+                isCrossRepository: true,
+              }),
+          }),
+        ),
+      );
+      const { manager } = yield* makeManager({ sourceControlProvider: provider });
+      const input = { cwd: repoDir, reference: "90", mode: "worktree" } as const;
+      const created = yield* preparePullRequestThread(manager, input);
+      const worktreePath = created.worktreePath!;
+      expect((yield* runGit(worktreePath, ["rev-parse", "HEAD"])).stdout.trim()).toBe(firstHead);
+
+      yield* runGit(repoDir, ["checkout", "author"]);
+      NodeFS.writeFileSync(NodePath.join(repoDir, "mr.txt"), "updated head\n");
+      yield* runGit(repoDir, ["add", "mr.txt"]);
+      yield* runGit(repoDir, ["commit", "-m", "Updated MR head"]);
+      yield* runGit(repoDir, ["push", "origin", "HEAD:refs/merge-requests/90/head"]);
+      const updatedHead = (yield* runGit(repoDir, ["rev-parse", "HEAD"])).stdout.trim();
+      const result = yield* preparePullRequestThread(manager, input);
+
+      expect(result.worktreePath && NodeFS.realpathSync.native(result.worktreePath)).toBe(
+        NodeFS.realpathSync.native(worktreePath),
+      );
+      expect(result.isOnPullRequestHead).toBe(true);
+      expect((yield* runGit(worktreePath, ["rev-parse", "HEAD"])).stdout.trim()).toBe(updatedHead);
+    }),
+  );
+
   it.effect("never moves an unrelated local branch that shares the fork head branch name", () =>
     Effect.gen(function* () {
       const repoDir = yield* makeTempDir("t3code-git-manager-");

apps/server/src/git/GitManager.ts

@@ -218,6 +218,7 @@ interface ResolvedPullRequest {
 }
 
 interface PullRequestHeadRemoteInfo {
+  provider?: SourceControlProviderKind | undefined;
   isCrossRepository?: boolean | undefined;
   headRepositoryNameWithOwner?: string | null | undefined;
   headRepositoryOwnerLogin?: string | null | undefined;
@@ -686,11 +687,13 @@ function shouldPreferSshRemote(url: string | null): boolean {
 }
 
 function toPullRequestHeadRemoteInfo(pr: {
+  provider: SourceControlProviderKind;
   isCrossRepository?: boolean | undefined;
   headRepositoryNameWithOwner?: string | null | undefined;
   headRepositoryOwnerLogin?: string | null | undefined;
 }): PullRequestHeadRemoteInfo {
   return {
+    provider: pr.provider,
     ...(pr.isCrossRepository !== undefined ? { isCrossRepository: pr.isCrossRepository } : {}),
     ...(pr.headRepositoryNameWithOwner !== undefined
       ? { headRepositoryNameWithOwner: pr.headRepositoryNameWithOwner }
@@ -953,6 +956,7 @@ export const make = Effect.gen(function* () {
         yield* gitCore.fetchPullRequestBranch({
           cwd,
           prNumber: pullRequest.number,
+          provider: pullRequest.provider,
           branch: localBranch,
         });
         return;
@@ -1000,6 +1004,7 @@ export const make = Effect.gen(function* () {
           .fetchPullRequestBranch({
             cwd,
             prNumber: pullRequest.number,
+            provider: pullRequest.provider,
             branch: localBranch,
           })
           .pipe(
@@ -2475,9 +2480,13 @@ export const make = Effect.gen(function* () {
           // head. The branch's upstream does not: configuring it is best-effort, so a branch cut
           // from `origin/main` whose head branch has since been deleted still resolves — and
           // following it would move the checkout onto main and call that the pull request.
-          .fetchPullRequestHeadCommit({ cwd: worktreePath, prNumber: pullRequest.number })
+          .fetchPullRequestHeadCommit({
+            cwd: worktreePath,
+            prNumber: pullRequest.number,
+            provider: pullRequestSummary.provider,
+          })
           .pipe(
-            // A host that publishes no `refs/pull/<n>/head` leaves the remote-tracking branch,
+            // A host that publishes no pull request head ref leaves the remote-tracking branch,
             // taken only where it is the head branch's own rather than whatever the checkout
             // happened to be cut from.
             Effect.catch(() =>

apps/server/src/vcs/GitVcsDriver.ts

@@ -12,6 +12,7 @@ import { ChildProcessSpawner } from "effect/process";
 
 import {
   GitCommandError,
+  type SourceControlProviderKind,
   VcsProcessExitError,
   type VcsSwitchRefInput,
   type VcsSwitchRefResult,
@@ -215,11 +216,13 @@ export interface GitFetchPullRequestBranchInput {
   cwd: string;
   prNumber: number;
   branch: string;
+  provider?: SourceControlProviderKind | undefined;
 }
 
 export interface GitFetchPullRequestHeadCommitInput {
   cwd: string;
   prNumber: number;
+  provider?: SourceControlProviderKind | undefined;
 }
 
 export interface GitResolveCommitInput {
@@ -357,7 +360,7 @@ export class GitVcsDriver extends Context.Service<
     readonly fetchPullRequestBranch: (
       input: GitFetchPullRequestBranchInput,
     ) => Effect.Effect<void, GitCommandError>;
-    /** Fetches `refs/pull/<n>/head` without writing a branch, for heads that exist nowhere else. */
+    /** Fetches the host's pull/merge request head ref without writing a branch. */
     readonly fetchPullRequestHeadCommit: (
       input: GitFetchPullRequestHeadCommitInput,
     ) => Effect.Effect<GitResolveCommitResult, GitCommandError>;

apps/server/src/vcs/GitVcsDriverCore.test.ts

@@ -3906,3 +3906,32 @@ it.layer(layerTest)("GitVcsDriver core integration", (it) => {
     );
   });
 });
+
+describe("pull request head refs", () => {
+  it.effect.each(["gitlab", "github"] as const)(
+    "fetches %s pull request heads without moving the checkout",
+    (provider) =>
+      Effect.gen(function* () {
+        const remote = yield* makeTmpDir();
+        yield* initRepoWithCommit(remote);
+        yield* writeTextFile(remote, "mr-head.txt", "remote head\n");
+        yield* git(remote, ["add", "mr-head.txt"]);
+        yield* git(remote, ["commit", "-m", "MR head"]);
+        const head = yield* git(remote, ["rev-parse", "HEAD"]);
+        const ref = provider === "gitlab" ? "refs/merge-requests/42/head" : "refs/pull/42/head";
+        yield* git(remote, ["update-ref", ref, head]);
+        const cwd = yield* makeTmpDir();
+        yield* initRepoWithCommit(cwd);
+        yield* git(cwd, ["remote", "add", "origin", remote]);
+        const original = yield* git(cwd, ["rev-parse", "HEAD"]);
+        assert.notStrictEqual(original, head);
+        const driver = yield* GitVcsDriver.GitVcsDriver;
+        yield* driver.fetchPullRequestBranch({ cwd, prNumber: 42, branch: "pr-42", provider });
+        assert.strictEqual(yield* git(cwd, ["rev-parse", "pr-42"]), head);
+        assert.strictEqual(yield* git(cwd, ["rev-parse", "HEAD"]), original);
+        const result = yield* driver.fetchPullRequestHeadCommit({ cwd, prNumber: 42, provider });
+        assert.strictEqual(result.commitSha, head);
+        assert.strictEqual(yield* git(cwd, ["rev-parse", "HEAD"]), original);
+      }).pipe(Effect.provide(layerTest)),
+  );
+});

apps/server/src/vcs/GitVcsDriverCore.ts

@@ -21,6 +21,7 @@ import { ChildProcess, ChildProcessSpawner } from "effect/process";
 import {
   GitCommandError,
   type GitCommandFailureReason,
+  type SourceControlProviderKind,
   T3_PROJECT_FILE_NAME,
   type ReviewDiffFileContentsInput,
   type ReviewDiffPreviewInput,
@@ -45,6 +46,8 @@ import {
 import * as ServerConfig from "../config.ts";
 
 const DEFAULT_TIMEOUT_MS = 30_000;
+const pullRequestHeadRef = (provider: SourceControlProviderKind | undefined, number: number) =>
+  provider === "gitlab" ? `refs/merge-requests/${number}/head` : `refs/pull/${number}/head`;
 const gitProcesses = Semaphore.makeUnsafe(8);
 // `git worktree add` checks out the full tree, so on large repositories it can
 // take well beyond the default 30s (e.g. a 375k-file repo takes ~40s on an idle
@@ -3507,7 +3510,7 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
           "--quiet",
           "--no-tags",
           remoteName,
-          `+refs/pull/${input.prNumber}/head:refs/heads/${input.branch}`,
+          `+${pullRequestHeadRef(input.provider, input.prNumber)}:refs/heads/${input.branch}`,
         ],
         {
           fallbackErrorDetail: "git fetch pull request branch failed",
@@ -3535,7 +3538,13 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
       yield* executeGit(
         "GitVcsDriver.fetchPullRequestHeadCommit",
         input.cwd,
-        ["fetch", "--quiet", "--no-tags", remoteName, `refs/pull/${input.prNumber}/head`],
+        [
+          "fetch",
+          "--quiet",
+          "--no-tags",
+          remoteName,
+          pullRequestHeadRef(input.provider, input.prNumber),
+        ],
         {
           fallbackErrorDetail: "git fetch pull request head failed",
         },