switch command (#51)

* switch cmd to interactively switch to another branch in the stack

* add switch to docs

* addressing review comments

* bump skill file version

* default to current branch

Author: skarim

cmd/merge_test.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/github/gh-stack/internal/config"
 	"github.com/github/gh-stack/internal/git"
+	"github.com/github/gh-stack/internal/github"
 	"github.com/github/gh-stack/internal/stack"
 	"github.com/stretchr/testify/assert"
 )
@@ -32,6 +33,7 @@ func TestMerge_NoPullRequest(t *testing.T) {
 	defer restore()
 
 	cfg, _, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)
@@ -65,6 +67,7 @@ func TestMerge_AlreadyMerged(t *testing.T) {
 	defer restore()
 
 	cfg, _, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)
@@ -104,6 +107,7 @@ func TestMerge_FullyMergedStack(t *testing.T) {
 	defer restore()
 
 	cfg, _, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)
@@ -136,6 +140,7 @@ func TestMerge_OnTrunk(t *testing.T) {
 	defer restore()
 
 	cfg, _, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)
@@ -168,6 +173,19 @@ func TestMerge_NonInteractive_PrintsURL(t *testing.T) {
 
 	// NewTestConfig is non-interactive (piped output), so no confirm prompt.
 	cfg, _, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{
+		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
+			if number == 42 {
+				return &github.PullRequest{
+					Number: 42,
+					ID:     "PR_42",
+					URL:    "https://github.com/owner/repo/pull/42",
+					State:  "OPEN",
+				}, nil
+			}
+			return nil, nil
+		},
+	}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)
@@ -196,6 +214,7 @@ func TestMerge_NoArgs(t *testing.T) {
 	defer restore()
 
 	cfg, _, _ := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)
@@ -229,6 +248,17 @@ func TestMerge_ByPRNumber(t *testing.T) {
 	defer restore()
 
 	cfg, _, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{
+		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
+			switch number {
+			case 42:
+				return &github.PullRequest{Number: 42, URL: "https://github.com/owner/repo/pull/42", State: "OPEN"}, nil
+			case 43:
+				return &github.PullRequest{Number: 43, URL: "https://github.com/owner/repo/pull/43", State: "OPEN"}, nil
+			}
+			return nil, nil
+		},
+	}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)
@@ -261,6 +291,14 @@ func TestMerge_ByPRURL(t *testing.T) {
 	defer restore()
 
 	cfg, _, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{
+		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
+			if number == 42 {
+				return &github.PullRequest{Number: 42, URL: "https://github.com/owner/repo/pull/42", State: "OPEN"}, nil
+			}
+			return nil, nil
+		},
+	}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)
@@ -293,6 +331,14 @@ func TestMerge_ByBranchName(t *testing.T) {
 	defer restore()
 
 	cfg, _, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{
+		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
+			if number == 42 {
+				return &github.PullRequest{Number: 42, URL: "https://github.com/owner/repo/pull/42", State: "OPEN"}, nil
+			}
+			return nil, nil
+		},
+	}
 	cmd := MergeCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)

cmd/push_test.go

@@ -84,7 +84,17 @@ func TestPush_NoSubmitHintWhenPRsExist(t *testing.T) {
 	defer restore()
 
 	cfg, _, errR := config.NewTestConfig()
-	cfg.GitHubClientOverride = &github.MockClient{}
+	cfg.GitHubClientOverride = &github.MockClient{
+		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
+			switch number {
+			case 10:
+				return &github.PullRequest{Number: 10, State: "OPEN", HeadRefName: "b1"}, nil
+			case 11:
+				return &github.PullRequest{Number: 11, State: "OPEN", HeadRefName: "b2"}, nil
+			}
+			return nil, nil
+		},
+	}
 	cmd := PushCmd(cfg)
 	cmd.SetOut(io.Discard)
 	cmd.SetErr(io.Discard)

cmd/submit_test.go

@@ -196,7 +196,12 @@ func TestSubmit_SkipsMergedBranches(t *testing.T) {
 	cfg, _, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
 		FindPRForBranchFn: func(branch string) (*github.PullRequest, error) {
-			return &github.PullRequest{Number: 2, URL: "https://github.com/owner/repo/pull/2"}, nil
+			// Only return an OPEN PR for the active branch (b2).
+			// Merged branches (b1, b3) should have no open PR.
+			if branch == "b2" {
+				return &github.PullRequest{Number: 2, URL: "https://github.com/owner/repo/pull/2", State: "OPEN"}, nil
+			}
+			return nil, nil
 		},
 	}
 	cmd := SubmitCmd(cfg)
@@ -1026,7 +1031,7 @@ func TestSubmit_PreflightCheck_SkippedWhenStackIDSet(t *testing.T) {
 	tmpDir := t.TempDir()
 	writeStackFile(t, tmpDir, s)
 
-	listStacksCalled := false
+	listStacksCallCount := 0
 	mock := newSubmitMock(tmpDir, "b1")
 	mock.PushFn = func(string, []string, bool, bool) error { return nil }
 	restore := git.SetOps(mock)
@@ -1035,8 +1040,17 @@ func TestSubmit_PreflightCheck_SkippedWhenStackIDSet(t *testing.T) {
 	cfg, _, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			listStacksCalled = true
-			return nil, &api.HTTPError{StatusCode: 404, Message: "Not Found"}
+			listStacksCallCount++
+			return []github.RemoteStack{{ID: 42, PullRequests: []int{10, 11}}}, nil
+		},
+		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
+			switch number {
+			case 10:
+				return &github.PullRequest{Number: 10, URL: "https://github.com/o/r/pull/10", HeadRefName: "b1", State: "OPEN"}, nil
+			case 11:
+				return &github.PullRequest{Number: 11, URL: "https://github.com/o/r/pull/11", HeadRefName: "b2", State: "OPEN"}, nil
+			}
+			return nil, nil
 		},
 		FindPRForBranchFn: func(string) (*github.PullRequest, error) {
 			return &github.PullRequest{Number: 10, URL: "https://github.com/o/r/pull/10"}, nil
@@ -1054,5 +1068,8 @@ func TestSubmit_PreflightCheck_SkippedWhenStackIDSet(t *testing.T) {
 	_, _ = io.ReadAll(errR)
 
 	assert.NoError(t, err)
-	assert.False(t, listStacksCalled, "ListStacks should not be called when stack ID already exists")
+	// ListStacks is called by syncStackPRs (remote sync), but NOT by the
+	// preflight check. Two syncStackPRs calls happen in submit (before and
+	// after PR creation), so expect exactly 2 ListStacks calls.
+	assert.Equal(t, 2, listStacksCallCount, "ListStacks should only be called by syncStackPRs, not by the preflight check")
 }

cmd/utils.go

@@ -11,6 +11,7 @@ import (
 	"github.com/cli/go-gh/v2/pkg/prompter"
 	"github.com/github/gh-stack/internal/config"
 	"github.com/github/gh-stack/internal/git"
+	"github.com/github/gh-stack/internal/github"
 	"github.com/github/gh-stack/internal/stack"
 )
 
@@ -231,27 +232,126 @@ func resolveStack(sf *stack.StackFile, branch string, cfg *config.Config) (*stac
 }
 
 // syncStackPRs discovers and updates pull request metadata for branches in a stack.
-// For each branch, it queries GitHub for the most recent PR and updates the
-// PullRequestRef including merge status. Branches with already-merged PRs are skipped.
+//
+// When the stack has a remote ID, the stack API is the source of truth: the
+// authoritative PR list is fetched from the server and matched to local
+// branches by head branch name. PRs remain associated even if closed.
+//
+// When no remote stack exists, branch-name-based discovery is used:
+//
+//  1. No tracked PR — look for an OPEN PR by head branch name.
+//  2. Tracked PR (not merged) — refresh status by number; if closed,
+//     clear the association and fall through to path 1.
+//  3. Tracked PR (merged) — skip; the merged state is final.
+//
 // The transient Queued flag is also populated from the API response.
 func syncStackPRs(cfg *config.Config, s *stack.Stack) {
 	client, err := cfg.GitHubClient()
 	if err != nil {
 		return
 	}
 
+	// When the stack has a remote ID, the stack API is the source of truth.
+	if s.ID != "" {
+		if syncStackPRsFromRemote(client, s) {
+			return
+		}
+	}
+
+	// No remote stack (or remote sync failed) — local discovery.
 	for i := range s.Branches {
 		b := &s.Branches[i]
 
 		if b.IsMerged() {
 			continue
 		}
 
-		pr, err := client.FindAnyPRForBranch(b.Branch)
+		if b.PullRequest != nil && b.PullRequest.Number != 0 {
+			// Tracked PR — refresh its state.
+			pr, err := client.FindPRByNumber(b.PullRequest.Number)
+			if err != nil {
+				continue // API error — keep existing tracked PR
+			}
+			if pr == nil {
+				// PR not found — clear stale ref and fall through
+				// to the open-PR lookup below.
+				b.PullRequest = nil
+				b.Queued = false
+			} else {
+				b.PullRequest = &stack.PullRequestRef{
+					Number: pr.Number,
+					ID:     pr.ID,
+					URL:    pr.URL,
+					Merged: pr.Merged,
+				}
+				b.Queued = pr.IsQueued()
+
+				// If the PR was closed (not merged), remove the association
+				// so we fall through to the open-PR lookup below.
+				if pr.State == "CLOSED" {
+					b.PullRequest = nil
+					b.Queued = false
+				} else {
+					continue
+				}
+			}
+		}
+
+		// No tracked PR (or just cleared) — only adopt OPEN PRs to avoid
+		// picking up stale merged/closed PRs from a previous use of this
+		// branch name.
+		pr, err := client.FindPRForBranch(b.Branch)
+		if err != nil || pr == nil {
+			continue
+		}
+		b.PullRequest = &stack.PullRequestRef{
+			Number: pr.Number,
+			ID:     pr.ID,
+			URL:    pr.URL,
+		}
+		b.Queued = pr.IsQueued()
+	}
+}
+
+// syncStackPRsFromRemote uses the stack API to sync PR state. The remote
+// stack's PR list is the source of truth — PRs stay associated even if
+// closed. Returns true if the sync succeeded, false if we should fall
+// back to local discovery (e.g. stack not found remotely, API error).
+func syncStackPRsFromRemote(client github.ClientOps, s *stack.Stack) bool {
+	stacks, err := client.ListStacks()
+	if err != nil {
+		return false
+	}
+
+	// Find our stack in the remote list.
+	var remotePRNumbers []int
+	for _, rs := range stacks {
+		if strconv.Itoa(rs.ID) == s.ID {
+			remotePRNumbers = rs.PullRequests
+			break
+		}
+	}
+	if remotePRNumbers == nil {
+		return false
+	}
+
+	// Fetch each remote PR's details and index by head branch name.
+	prByBranch := make(map[string]*github.PullRequest, len(remotePRNumbers))
+	for _, num := range remotePRNumbers {
+		pr, err := client.FindPRByNumber(num)
 		if err != nil || pr == nil {
 			continue
 		}
+		prByBranch[pr.HeadRefName] = pr
+	}
 
+	// Match remote PRs to local branches.
+	for i := range s.Branches {
+		b := &s.Branches[i]
+		pr, ok := prByBranch[b.Branch]
+		if !ok {
+			continue
+		}
 		b.PullRequest = &stack.PullRequestRef{
 			Number: pr.Number,
 			ID:     pr.ID,
@@ -260,6 +360,8 @@ func syncStackPRs(cfg *config.Config, s *stack.Stack) {
 		}
 		b.Queued = pr.IsQueued()
 	}
+
+	return true
 }
 
 // updateBaseSHAs refreshes the Base and Head SHAs for all active branches