Enable Git long paths for clone and fetch

cache.go

@@ -83,8 +83,8 @@ func (c *Cache) EnsureCommit(ctx context.Context, url, commit string) error {
 		return nil
 	}
 	out, err := doPinnedURL(ctx, policy, url, Command{
-		Args:  []string{"fetch", "--unshallow", "--quiet", "origin"}, //nolint:goconst // Git argv is clearer with literal subcommands and flags.
-		Label: "fetch",                                               //nolint:goconst // Retry notices use the literal Git subcommand.
+		Args:  longPathArgs("fetch", "--unshallow", "--quiet", "origin"), //nolint:goconst // Git argv is clearer with literal subcommands and flags.
+		Label: "fetch",                                                   //nolint:goconst // Retry notices use the literal Git subcommand.
 		Dir:   cacheSrc,
 		Env:   remoteEnv(),
 	})

cache_test.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"os"
 	"path/filepath"
+	"slices"
 	"strings"
 	"testing"
 	"time"
@@ -191,6 +192,40 @@ func TestCacheEnsureCommitRetriesUnshallowFetch(t *testing.T) {
 	}
 }
 
+func TestCacheEnsureCommitConfiguresLongPathsForFetch(t *testing.T) {
+	cache := Cache{Root: t.TempDir()}
+	url := "https://example.invalid/repo"
+	cacheSrc := filepath.Join(cache.Dir(url), "src")
+	if err := os.MkdirAll(filepath.Join(cacheSrc, ".git"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+
+	var fetchArgs []string
+	cache.Retry = Retry{
+		Run: func(_ context.Context, _ string, _ []string, args ...string) (string, error) {
+			switch subcommand(args) {
+			case "cat-file":
+				return "", errors.New("missing object")
+			case "rev-parse":
+				return "true\n", nil
+			case "fetch":
+				fetchArgs = append([]string(nil), args...)
+				return "", nil
+			default:
+				return "", errors.New("unexpected Git command")
+			}
+		},
+	}
+
+	if err := cache.EnsureCommit(context.Background(), url, "deadbeef"); err != nil {
+		t.Fatalf("EnsureCommit: %v", err)
+	}
+	want := []string{"-c", "core.longpaths=true"}
+	if len(fetchArgs) < len(want) || !slices.Equal(fetchArgs[:len(want)], want) {
+		t.Errorf("fetch args = %v, want prefix %v", fetchArgs, want)
+	}
+}
+
 func TestCacheEnsureCommitSkipsUnreachableCommitInFullClone(t *testing.T) {
 	cache := Cache{Root: t.TempDir()}
 	url := "https://example.invalid/repo"

ensure.go

@@ -84,7 +84,7 @@ func ensure(ctx context.Context, retry Retry, url, dst, ref string, options Ensu
 	out, err := doPinnedURL(ctx, retry, url, Command{
 		Label: "clone",
 		Env:   remoteEnv(),
-		Args:  args,
+		Args:  longPathArgs(args...),
 		Reset: DestReset(dst),
 	})
 	if err != nil {
@@ -141,7 +141,7 @@ func fetchRef(ctx context.Context, retry Retry, url, dst, ref string, full bool)
 	out, err := doPinnedURL(ctx, policy, url, Command{
 		Label: "fetch", //nolint:goconst // Retry notices use the literal Git subcommand.
 		Env:   remoteEnv(),
-		Args:  args,
+		Args:  longPathArgs(args...),
 	})
 	if err != nil {
 		return fmt.Errorf("%s: %w", strings.TrimSpace(out), err)

ensure_test.go

@@ -379,6 +379,29 @@ func TestEnsureRetriesCloneAndResetsPartialDestination(t *testing.T) {
 	}
 }
 
+func TestEnsureConfiguresLongPathsForCloneAndFetch(t *testing.T) {
+	dst := filepath.Join(t.TempDir(), "checkout")
+	commands := make(map[string][]string)
+	retry := Retry{
+		Run: func(_ context.Context, _ string, _ []string, args ...string) (string, error) {
+			commands[subcommand(args)] = append([]string(nil), args...)
+			return "", nil
+		},
+	}
+
+	err := Ensure(context.Background(), retry, "https://example.invalid/repo", dst, "main", false)
+	if err != nil {
+		t.Fatalf("Ensure: %v", err)
+	}
+	for _, command := range []string{"clone", "fetch"} {
+		args := commands[command]
+		want := []string{"-c", "core.longpaths=true"}
+		if len(args) < len(want) || !slices.Equal(args[:len(want)], want) {
+			t.Errorf("%s args = %v, want prefix %v", command, args, want)
+		}
+	}
+}
+
 func TestEnsureUnknownRefReturnsUnreachableError(t *testing.T) {
 	origin := newOriginFixture(t)
 	dst := filepath.Join(t.TempDir(), "checkout")

run.go

@@ -28,6 +28,10 @@ func remoteEnv() []string {
 	return env
 }
 
+func longPathArgs(args ...string) []string {
+	return append([]string{"-c", "core.longpaths=true"}, args...)
+}
+
 // Runner runs one Git invocation and returns its combined output.
 type Runner func(ctx context.Context, dir string, env []string, args ...string) (string, error)