Implement forge pr view for current branch

internal/cli/pr.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -48,20 +49,32 @@ func prViewCmd() *cobra.Command {
 	)
 
 	cmd := &cobra.Command{
-		Use:   "view <number>",
+		Use:   "view [<number>]",
 		Short: "View a pull request",
-		Args:  cobra.ExactArgs(1),
-		RunE: func(cmd *cobra.Command, args []string) error {
-			number, err := strconv.Atoi(args[0])
-			if err != nil {
-				return fmt.Errorf("invalid PR number: %s", args[0])
-			}
+		Long: `View a pull request by number, or view the PR for the current branch.
 
+If no number is given, finds and displays the pull request whose head
+branch matches the current git branch.`,
+		Args: cobra.MaximumNArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
 			forge, owner, repoName, _, err := resolve.Repo(flagRepo, flagForgeType)
 			if err != nil {
 				return err
 			}
 
+			var number int
+			if len(args) > 0 {
+				number, err = strconv.Atoi(args[0])
+				if err != nil {
+					return fmt.Errorf("invalid PR number: %s", args[0])
+				}
+			} else {
+				number, err = findPRForCurrentBranch(cmd.Context(), forge, owner, repoName)
+				if err != nil {
+					return err
+				}
+			}
+
 			pr, err := forge.PullRequests().Get(cmd.Context(), owner, repoName, number)
 			if err != nil {
 				return fmt.Errorf("getting PR #%d: %w", number, err)
@@ -610,10 +623,13 @@ The argument can be a PR number or a full URL:
 				localBranch = flagBranch
 			}
 
+			if !flagDetach {
+				_ = storePRForBranch(ctx, localBranch, number)
+			}
+
 			if pr.Head.Fork != nil {
 				return checkoutForkPR(ctx, domain, pr, remoteRef, localBranch, flagRemoteName, flagDetach, flagForce)
 			}
-
 			return checkoutSameRepoPR(ctx, remoteRef, localBranch, flagDetach, flagForce)
 		},
 	}
@@ -744,3 +760,94 @@ func gitCheckout(ctx context.Context, remote, remoteRef, localBranch string, det
 	resetCmd.Stderr = os.Stderr
 	return resetCmd.Run()
 }
+
+func findPRForCurrentBranch(ctx context.Context, f forges.Forge, owner, repo string) (int, error) {
+	out, err := exec.CommandContext(ctx, "git", "branch", "--show-current").Output()
+	if err != nil {
+		return 0, fmt.Errorf("getting current branch: %w (not in a git repository?)", err)
+	}
+	localBranch := strings.TrimSpace(string(out))
+	if localBranch == "" {
+		return 0, fmt.Errorf("not on a branch (detached HEAD state)")
+	}
+
+	// Check cache first (set by 'pr checkout')
+	if n, err := loadPRForBranch(ctx, localBranch); err == nil {
+		return n, nil
+	}
+
+	// If that yields nothing, fall back to API query. This API call is really
+	// slow for Gitea since the Head filter is not actually implemented.
+	headOwner := owner
+	if remoteOwner, err := resolve.OwnerForBranch(localBranch); err == nil {
+		headOwner = remoteOwner
+	}
+
+	prs, err := f.PullRequests().List(ctx, owner, repo, forges.ListPROpts{
+		Head:  headOwner + ":" + localBranch,
+		State: "all",
+		Limit: 100,
+	})
+	if err != nil {
+		return 0, fmt.Errorf("listing PRs for branch %q: %w", localBranch, err)
+	}
+
+	// Need to filter the results again for owner:branch since the API results
+	// don't respect the filter in case of Gitea.
+	var matching []forges.PullRequest
+	for _, pr := range prs {
+		prHeadOwner := owner
+		if pr.Head.Fork != nil {
+			prHeadOwner = pr.Head.Fork.Owner
+		}
+		if pr.Head.Ref == localBranch && prHeadOwner == headOwner {
+			matching = append(matching, pr)
+		}
+	}
+
+	if len(matching) < 1 {
+		return 0, fmt.Errorf("no pull request found for branch %q", localBranch)
+	}
+
+	if len(matching) > 1 {
+		return 0, fmt.Errorf("multiple pull request found for branch %q, might be a bug?", localBranch)
+	}
+
+	for _, pr := range matching {
+		if pr.State == "open" {
+			// Store the PR number into local git config so that the new 'forge
+			// pr view' call is a lot faster.
+			_ = storePRForBranch(ctx, localBranch, pr.Number)
+			return pr.Number, nil
+		}
+	}
+
+	return 0, fmt.Errorf("no matching pull request found for branch %q", localBranch)
+}
+
+func storePRForBranch(ctx context.Context, branch string, number int) error {
+	key := fmt.Sprintf("branch.%s.forge-pr", branch)
+	return exec.CommandContext(ctx, "git", "config", "--local", key, strconv.Itoa(number)).Run()
+}
+
+var prRefRE = regexp.MustCompile(`^refs/pull/(\d+)/head$`)
+
+func loadPRForBranch(ctx context.Context, branch string) (int, error) {
+	key := fmt.Sprintf("branch.%s.forge-pr", branch)
+	out, err := exec.CommandContext(ctx, "git", "config", "--get", key).Output()
+	if err == nil {
+		return strconv.Atoi(strings.TrimSpace(string(out)))
+	}
+
+	// Fall back to gh CLI's format (refs/pull/<n>/head in branch.<name>.merge)
+	mergeKey := fmt.Sprintf("branch.%s.merge", branch)
+	out, err = exec.CommandContext(ctx, "git", "config", "--get", mergeKey).Output()
+	if err != nil {
+		return 0, err
+	}
+	m := prRefRE.FindStringSubmatch(strings.TrimSpace(string(out)))
+	if m == nil {
+		return 0, fmt.Errorf("not a PR ref")
+	}
+	return strconv.Atoi(m[1])
+}

internal/cli/pr_checkout_test.go

@@ -15,16 +15,18 @@ import (
 
 // mockPRService implements forges.PullRequestService for testing.
 type mockPRService struct {
-	pr  *forges.PullRequest
-	err error
+	pr         *forges.PullRequest
+	err        error
+	listResult []forges.PullRequest
+	listErr    error
 }
 
 func (m *mockPRService) Get(_ context.Context, _, _ string, _ int) (*forges.PullRequest, error) {
 	return m.pr, m.err
 }
 
 func (m *mockPRService) List(_ context.Context, _, _ string, _ forges.ListPROpts) ([]forges.PullRequest, error) {
-	return nil, nil
+	return m.listResult, m.listErr
 }
 
 func (m *mockPRService) Create(_ context.Context, _, _ string, _ forges.CreatePROpts) (*forges.PullRequest, error) {

internal/cli/pr_test.go

@@ -2,8 +2,15 @@ package cli
 
 import (
 	"bytes"
+	"context"
+	"os"
+	"os/exec"
+	"path/filepath"
 	"strings"
 	"testing"
+
+	"github.com/git-pkgs/forge"
+	"github.com/git-pkgs/forge/internal/resolve"
 )
 
 func TestPRCmd(t *testing.T) {
@@ -74,18 +81,6 @@ func TestPRViewInvalidNumber(t *testing.T) {
 	}
 }
 
-func TestPRViewRequiresArg(t *testing.T) {
-	var buf bytes.Buffer
-	rootCmd.SetOut(&buf)
-	rootCmd.SetErr(&buf)
-	rootCmd.SetArgs([]string{"pr", "view"})
-
-	err := rootCmd.Execute()
-	if err == nil {
-		t.Fatal("expected error for missing argument")
-	}
-}
-
 func TestPRCreateRequiresTitleAndHead(t *testing.T) {
 	var buf bytes.Buffer
 	rootCmd.SetOut(&buf)
@@ -142,3 +137,146 @@ func TestPRDiffRequiresArg(t *testing.T) {
 		t.Fatal("expected error for missing argument")
 	}
 }
+
+func TestStorePRForBranch(t *testing.T) {
+	if _, err := exec.LookPath("git"); err != nil {
+		t.Skip("git not installed")
+	}
+
+	dir := t.TempDir()
+	t.Chdir(dir)
+
+	mustGitCmd(t, "init", "-q")
+	mustGitCmd(t, "config", "user.email", "test@test.com")
+	mustGitCmd(t, "config", "user.name", "Test")
+
+	if err := os.WriteFile(filepath.Join(dir, "README"), []byte("test"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	mustGitCmd(t, "add", "README")
+	mustGitCmd(t, "commit", "-m", "init")
+	mustGitCmd(t, "checkout", "-b", "feature")
+
+	ctx := context.Background()
+
+	// Store PR number
+	if err := storePRForBranch(ctx, "feature", 42); err != nil {
+		t.Fatalf("storePRForBranch: %v", err)
+	}
+
+	// Load it back
+	n, err := loadPRForBranch(ctx, "feature")
+	if err != nil {
+		t.Fatalf("loadPRForBranch: %v", err)
+	}
+	if n != 42 {
+		t.Errorf("got %d, want 42", n)
+	}
+}
+
+func TestLoadPRForBranchGhFormat(t *testing.T) {
+	if _, err := exec.LookPath("git"); err != nil {
+		t.Skip("git not installed")
+	}
+
+	dir := t.TempDir()
+	t.Chdir(dir)
+
+	mustGitCmd(t, "init", "-q")
+	mustGitCmd(t, "config", "user.email", "test@test.com")
+	mustGitCmd(t, "config", "user.name", "Test")
+
+	if err := os.WriteFile(filepath.Join(dir, "README"), []byte("test"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	mustGitCmd(t, "add", "README")
+	mustGitCmd(t, "commit", "-m", "init")
+	mustGitCmd(t, "checkout", "-b", "pr-branch")
+
+	// Set up gh CLI's format: branch.<name>.merge = refs/pull/<n>/head
+	mustGitCmd(t, "config", "branch.pr-branch.merge", "refs/pull/123/head")
+
+	ctx := context.Background()
+	n, err := loadPRForBranch(ctx, "pr-branch")
+	if err != nil {
+		t.Fatalf("loadPRForBranch: %v", err)
+	}
+	if n != 123 {
+		t.Errorf("got %d, want 123", n)
+	}
+}
+
+func TestFindPRForCurrentBranch(t *testing.T) {
+	if _, err := exec.LookPath("git"); err != nil {
+		t.Skip("git not installed")
+	}
+
+	dir := t.TempDir()
+	t.Chdir(dir)
+
+	mustGitCmd(t, "init", "-q")
+	mustGitCmd(t, "config", "user.email", "test@test.com")
+	mustGitCmd(t, "config", "user.name", "Test")
+	mustGitCmd(t, "remote", "add", "origin", "https://github.com/testowner/testrepo.git")
+
+	if err := os.WriteFile(filepath.Join(dir, "README"), []byte("test"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	mustGitCmd(t, "add", "README")
+	mustGitCmd(t, "commit", "-m", "init")
+	mustGitCmd(t, "checkout", "-b", "feature")
+	mustGitCmd(t, "config", "branch.feature.remote", "origin")
+
+	// Set up mock forge that returns a PR for our branch
+	mockPR := &mockPRService{
+		listResult: []forges.PullRequest{
+			{
+				Number: 99,
+				State:  "open",
+				Head: forges.PRBranch{
+					Ref: "feature",
+				},
+			},
+		},
+	}
+	resolve.SetTestForge(
+		&mockForge{prService: mockPR},
+		"testowner", "testrepo", "github.com",
+	)
+	t.Cleanup(resolve.ResetTestForge)
+
+	ctx := context.Background()
+	forge, owner, repo, _, err := resolve.Repo("", "")
+	if err != nil {
+		t.Fatalf("resolve.Repo: %v", err)
+	}
+
+	n, err := findPRForCurrentBranch(ctx, forge, owner, repo)
+	if err != nil {
+		t.Fatalf("findPRForCurrentBranch: %v", err)
+	}
+	if n != 99 {
+		t.Errorf("got %d, want 99", n)
+	}
+
+	// The PR number should now be cached
+	cached, err := loadPRForBranch(ctx, "feature")
+	if err != nil {
+		t.Fatalf("loadPRForBranch after find: %v", err)
+	}
+	if cached != 99 {
+		t.Errorf("cached PR = %d, want 99", cached)
+	}
+}
+
+func mustGitCmd(t *testing.T, args ...string) {
+	t.Helper()
+	cmd := exec.Command("git", args...)
+	cmd.Env = append(os.Environ(),
+		"GIT_CONFIG_GLOBAL=/dev/null",
+		"GIT_CONFIG_SYSTEM=/dev/null",
+	)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("git %v: %v\n%s", args, err, out)
+	}
+}

internal/resolve/resolve.go

@@ -211,6 +211,32 @@ func gitRemoteURL(name string) (string, error) {
 	return strings.TrimSpace(string(out)), nil
 }
 
+// OwnerForBranch returns the repository owner for the remote that the given
+// branch tracks. This is useful for determining which fork a branch was pushed
+// to when creating pull requests.
+func OwnerForBranch(branch string) (string, error) {
+	remoteKey := fmt.Sprintf("branch.%s.remote", branch)
+	out, err := exec.Command("git", "config", "--get", remoteKey).Output()
+	if err != nil {
+		return "", err
+	}
+	remote := strings.TrimSpace(string(out))
+	if remote == "" {
+		return "", fmt.Errorf("no remote configured")
+	}
+
+	remoteURL, err := gitRemoteURL(remote)
+	if err != nil {
+		return "", err
+	}
+
+	_, owner, _, err := forges.ParseRepoURL(remoteURL)
+	if err != nil {
+		return "", err
+	}
+	return owner, nil
+}
+
 func newClient(domain string) *forges.Client {
 	token := TokenForDomain(domain)
 	var opts []forges.Option