Fix rebase when upstack head has moved

cmd/rebase_test.go

@@ -2843,6 +2843,57 @@ func TestIntegration_AmendedParentWithoutForkPointFailsSafely(t *testing.T) {
 	assert.Equal(t, childBefore, issue250Git(t, repo.dir, "rev-parse", "child"))
 }
 
+func TestRebase_ImportedStackAfterParentAdvance(t *testing.T) {
+	repo := setupIssue512Repo(t)
+	issue250Git(t, repo.dir, "checkout", "parent")
+	issue250WriteFile(t, repo.dir, "parent-extra.txt", "new parent content\n")
+	issue250Git(t, repo.dir, "add", "parent-extra.txt")
+	issue250Git(t, repo.dir, "commit", "-m", "parent extra")
+	issue250Git(t, repo.dir, "push", "origin", "parent")
+	newParent := issue250Git(t, repo.dir, "rev-parse", "parent")
+
+	prs := []*github.PullRequest{
+		{Number: 10, HeadRefName: "parent", BaseRefName: "main", BaseRefOID: repo.main, State: "OPEN"},
+		{Number: 11, HeadRefName: "child", BaseRefName: "parent", BaseRefOID: repo.parent, State: "OPEN"},
+	}
+	remote := github.RemoteStack{
+		ID: 1, Number: 1, Base: github.RemoteStackBase{Ref: "main"}, PullRequests: []int{10, 11},
+	}
+	cfg := issue250TestConfig(t)
+	cfg.GitHubClientOverride = &github.MockClient{
+		ListStacksFn: func() ([]github.RemoteStack, error) {
+			return []github.RemoteStack{remote}, nil
+		},
+		GetStackFn: func(int) (*github.RemoteStack, error) { return &remote, nil },
+		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
+			return prs[number-10], nil
+		},
+	}
+	withIssue250Repo(t, repo.writer)
+	gitDir := filepath.Join(repo.writer, ".git")
+	sf, err := stack.Load(gitDir)
+	require.NoError(t, err)
+	s, err := importRemoteStack(cfg, sf, gitDir, "origin", "main", prs, "1", 1)
+	require.NoError(t, err)
+	require.Equal(t, newParent, s.Branches[1].Base)
+	require.NoError(t, stack.Save(gitDir, sf))
+	issue250Git(t, repo.writer, "checkout", "child")
+	forkPoint, err := git.MergeBaseForkPoint("parent", "child")
+	require.NoError(t, err)
+	require.Empty(t, forkPoint)
+
+	require.NoError(t, runRebase(cfg, &rebaseOptions{remote: "origin"}))
+
+	assert.Equal(t, newParent, issue250Git(t, repo.writer, "merge-base", "parent", "child"))
+	assert.Equal(t, "child only", issue250Git(t, repo.writer, "log", "--format=%s", "parent..child"))
+	assert.Equal(t, "new parent content", issue250Git(t, repo.writer, "show", "child:parent-extra.txt"))
+	assert.Equal(t, "child", issue250Git(t, repo.writer, "show", "child:child.txt"))
+	sf, err = stack.Load(gitDir)
+	require.NoError(t, err)
+	assert.Equal(t, newParent, sf.Stacks[0].Branches[1].Base)
+	assert.NoFileExists(t, filepath.Join(gitDir, rebaseStateFile))
+}
+
 func TestIntegration_AdoptedBranchRebasesFromCommonAncestor(t *testing.T) {
 	remoteDir := filepath.Join(t.TempDir(), "remote.git")
 	cloneDir := filepath.Join(t.TempDir(), "clone")

cmd/utils.go

@@ -549,7 +549,7 @@ func syncStackPRs(cfg *config.Config, s *stack.Stack) map[string]*github.PRDetai
 	// Each branch is processed concurrently; results are collected and applied sequentially.
 	type branchResult struct {
 		index       int
-		pullRequest *stack.PullRequestRef
+		pullRequest *github.PullRequest
 		queued      bool
 		details     *github.PRDetails
 		skip        bool // true means keep existing data, don't update
@@ -603,7 +603,7 @@ func syncStackPRs(cfg *config.Config, s *stack.Stack) map[string]*github.PRDetai
 				}
 				if pr != nil && pr.State != "CLOSED" {
 					// PR is open or merged — keep it
-					res.pullRequest = pullRequestRef(pr, branch.PullRequest)
+					res.pullRequest = pr
 					res.queued = pr.IsQueued()
 					res.details = prDetailsFromPR(pr)
 					results[idx] = res
@@ -622,7 +622,7 @@ func syncStackPRs(cfg *config.Config, s *stack.Stack) map[string]*github.PRDetai
 				results[idx] = res
 				return
 			}
-			res.pullRequest = pullRequestRef(pr, nil)
+			res.pullRequest = pr
 			res.queued = pr.IsQueued()
 			// FindPRForBranch only returns OPEN PRs
 			res.details = &github.PRDetails{
@@ -651,8 +651,9 @@ func syncStackPRs(cfg *config.Config, s *stack.Stack) map[string]*github.PRDetai
 		}
 		b := &s.Branches[res.index]
 		if res.pullRequest != nil {
-			b.PullRequest = res.pullRequest
+			b.PullRequest = pullRequestRef(res.pullRequest, b.PullRequest)
 			b.Queued = res.queued
+			updateBaseFromPR(s, b, res.pullRequest)
 		} else if !b.IsMerged() {
 			// Clear if we didn't find anything (and original was cleared during discovery)
 			if b.PullRequest != nil && res.pullRequest == nil {
@@ -694,6 +695,16 @@ func pullRequestRef(pr *github.PullRequest, previous *stack.PullRequestRef) *sta
 	return ref
 }
 
+func updateBaseFromPR(s *stack.Stack, b *stack.BranchRef, pr *github.PullRequest) {
+	if b.IsMerged() || pr.BaseRefOID == "" || pr.BaseRefName != s.ActiveBaseBranch(b.Branch) {
+		return
+	}
+	// A PR retains its old parent tip even when a fresh clone has no reflog for it.
+	if canUpdateBase(pr.BaseRefOID, b.Branch, b.Base) {
+		b.Base = pr.BaseRefOID
+	}
+}
+
 // prDetailsFromPR builds PRDetails from a PullRequest returned by FindPRByNumber.
 func prDetailsFromPR(pr *github.PullRequest) *github.PRDetails {
 	if pr == nil {
@@ -854,6 +865,7 @@ func syncStackPRsFromRemote(client github.ClientOps, s *stack.Stack) (map[string
 		}
 		b.PullRequest = pullRequestRef(pr, b.PullRequest)
 		b.Queued = pr.IsQueued()
+		updateBaseFromPR(s, b, pr)
 		details[b.Branch] = prDetailsFromPR(pr)
 	}
 

cmd/utils_test.go

@@ -1261,10 +1261,12 @@ func TestSyncStackPRs_NoTrackedPR_AdoptsOpenPR(t *testing.T) {
 	cfg.GitHubClientOverride = &github.MockClient{
 		FindPRForBranchFn: func(branch string) (*github.PullRequest, error) {
 			return &github.PullRequest{
-				Number: 99,
-				ID:     "PR_99",
-				URL:    "https://github.com/o/r/pull/99",
-				State:  "OPEN",
+				Number:      99,
+				ID:          "PR_99",
+				URL:         "https://github.com/o/r/pull/99",
+				State:       "OPEN",
+				BaseRefName: "main",
+				BaseRefOID:  "base-sha",
 			}, nil
 		},
 	}
@@ -1275,6 +1277,34 @@ func TestSyncStackPRs_NoTrackedPR_AdoptsOpenPR(t *testing.T) {
 	require.NotNil(t, s.Branches[0].PullRequest)
 	assert.Equal(t, 99, s.Branches[0].PullRequest.Number)
 	assert.False(t, s.Branches[0].PullRequest.Merged)
+	assert.Equal(t, "base-sha", s.Branches[0].Base)
+}
+
+func TestSyncStackPRs_PreservesDifferentLocalBaseBranch(t *testing.T) {
+	s := &stack.Stack{
+		Trunk: stack.BranchRef{Branch: "main"},
+		Branches: []stack.BranchRef{{
+			Branch: "feature", Base: "local-base", PullRequest: &stack.PullRequestRef{Number: 99},
+		}},
+	}
+	restore := git.SetOps(&git.MockOps{
+		IsAncestorFn: func(a, b string) (bool, error) {
+			return a == "remote-base" && b == "feature", nil
+		},
+	})
+	defer restore()
+	cfg := issue250TestConfig(t)
+	cfg.GitHubClientOverride = &github.MockClient{
+		FindPRByNumberFn: func(int) (*github.PullRequest, error) {
+			return &github.PullRequest{
+				Number: 99, State: "OPEN", BaseRefName: "previous-parent", BaseRefOID: "remote-base",
+			}, nil
+		},
+	}
+
+	syncStackPRs(cfg, s)
+
+	assert.Equal(t, "local-base", s.Branches[0].Base)
 }
 
 func TestSyncStackPRs_TrackedPR_DetectsMerge(t *testing.T) {

internal/github/github.go

@@ -35,6 +35,7 @@ type PullRequest struct {
 	HeadRefName      string            `graphql:"headRefName"`
 	HeadRefOID       string            `graphql:"headRefOid"`
 	BaseRefName      string            `graphql:"baseRefName"`
+	BaseRefOID       string            `graphql:"baseRefOid"`
 	IsDraft          bool              `graphql:"isDraft"`
 	Merged           bool              `graphql:"merged"`
 	MergeQueueEntry  *MergeQueueEntry  `graphql:"mergeQueueEntry"`
@@ -116,6 +117,7 @@ func (c *Client) FindPRForBranch(branch string) (*PullRequest, error) {
 					Title            string            `graphql:"title"`
 					Body             string            `graphql:"body"`
 					BaseRefName      string            `graphql:"baseRefName"`
+					BaseRefOID       string            `graphql:"baseRefOid"`
 					IsDraft          bool              `graphql:"isDraft"`
 					MergeQueueEntry  *MergeQueueEntry  `graphql:"mergeQueueEntry"`
 					AutoMergeRequest *AutoMergeRequest `graphql:"autoMergeRequest"`
@@ -147,6 +149,7 @@ func (c *Client) FindPRForBranch(branch string) (*PullRequest, error) {
 		Title:            n.Title,
 		Body:             n.Body,
 		BaseRefName:      n.BaseRefName,
+		BaseRefOID:       n.BaseRefOID,
 		IsDraft:          n.IsDraft,
 		MergeQueueEntry:  n.MergeQueueEntry,
 		AutoMergeRequest: n.AutoMergeRequest,
@@ -376,6 +379,7 @@ func (c *Client) FindPRByNumber(number int) (*PullRequest, error) {
 				HeadRefName      string            `graphql:"headRefName"`
 				HeadRefOID       string            `graphql:"headRefOid"`
 				BaseRefName      string            `graphql:"baseRefName"`
+				BaseRefOID       string            `graphql:"baseRefOid"`
 				IsDraft          bool              `graphql:"isDraft"`
 				Merged           bool              `graphql:"merged"`
 				MergeQueueEntry  *MergeQueueEntry  `graphql:"mergeQueueEntry"`
@@ -408,6 +412,7 @@ func (c *Client) FindPRByNumber(number int) (*PullRequest, error) {
 		HeadRefName:      n.HeadRefName,
 		HeadRefOID:       n.HeadRefOID,
 		BaseRefName:      n.BaseRefName,
+		BaseRefOID:       n.BaseRefOID,
 		IsDraft:          n.IsDraft,
 		Merged:           n.Merged,
 		MergeQueueEntry:  n.MergeQueueEntry,

internal/github/github_test.go

@@ -118,6 +118,7 @@ func TestFindPRByNumber_MergedHead(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			pr := map[string]any{
 				"number": 42, "state": "MERGED", "merged": true, "headRefName": "feature",
+				"baseRefOid": "previous-base",
 			}
 			if !tt.omit {
 				pr["headRefOid"] = tt.head
@@ -132,6 +133,7 @@ func TestFindPRByNumber_MergedHead(t *testing.T) {
 				}
 				require.NoError(t, json.NewDecoder(r.Body).Decode(&request))
 				assert.Contains(t, request.Query, "headRefOid")
+				assert.Contains(t, request.Query, "baseRefOid")
 				return &http.Response{
 					StatusCode: http.StatusOK,
 					Body:       io.NopCloser(bytes.NewReader(body)),
@@ -150,6 +152,7 @@ func TestFindPRByNumber_MergedHead(t *testing.T) {
 			require.NotNil(t, got)
 			assert.True(t, got.Merged)
 			assert.Equal(t, tt.head, got.HeadRefOID)
+			assert.Equal(t, "previous-base", got.BaseRefOID)
 		})
 	}
 }