format/commitgraph: Add initial commit-graph support

6 files changed, 113 insertions, 10 deletions

diff --git a/internal/intconv/intconv.go b/internal/intconv/intconv.go
index ab9d5c63..08530265 100644
--- a/internal/intconv/intconv.go
+++ b/internal/intconv/intconv.go
@@ -86,3 +86,12 @@ func Uint32ToUint8(v uint32) (uint8, error) {
 
 	return uint8(v), nil
 }
+
+// Uint32ToInt converts v to int, returning an error if it overflows.
+func Uint32ToInt(v uint32) (int, error) {
+	if uint64(v) > uint64(math.MaxInt) {
+		return 0, fmt.Errorf("intconv: uint32 %d overflows int", v)
+	}
+
+	return int(v), nil
+}
diff --git a/internal/testgit/repo_commit_graph_write.go b/internal/testgit/repo_commit_graph_write.go
new file mode 100644
index 00000000..13221f87
--- /dev/null
+++ b/internal/testgit/repo_commit_graph_write.go
@@ -0,0 +1,13 @@
+package testgit
+
+import "testing"
+
+// CommitGraphWrite runs "git commit-graph write" with args in the repository.
+func (testRepo *TestRepo) CommitGraphWrite(tb testing.TB, args ...string) {
+	tb.Helper()
+
+	cmdArgs := make([]string, 0, len(args)+3)
+	cmdArgs = append(cmdArgs, "commit-graph", "write")
+	cmdArgs = append(cmdArgs, args...)
+	_ = testRepo.Run(tb, cmdArgs...)
+}
diff --git a/internal/testgit/repo_from_fixture.go b/internal/testgit/repo_from_fixture.go
new file mode 100644
index 00000000..887bf9a3
--- /dev/null
+++ b/internal/testgit/repo_from_fixture.go
@@ -0,0 +1,35 @@
+package testgit
+
+import (
+	"io/fs"
+	"os"
+	"testing"
+
+	"codeberg.org/lindenii/furgit/objectid"
+)
+
+// NewRepoFromFixture copies one existing repository fixture into a temp dir.
+func NewRepoFromFixture(tb testing.TB, algo objectid.Algorithm, fixtureDir string) *TestRepo {
+	tb.Helper()
+
+	if algo.Size() == 0 {
+		tb.Fatalf("invalid algorithm: %v", algo)
+	}
+
+	dst := tb.TempDir()
+	srcFS := os.DirFS(fixtureDir)
+	err := copyFS(dst, srcFS)
+	if err != nil {
+		tb.Fatalf("copy fixture %q: %v", fixtureDir, err)
+	}
+
+	return &TestRepo{
+		dir:  dst,
+		algo: algo,
+		env:  defaultEnv(),
+	}
+}
+
+func copyFS(dst string, src fs.FS) error {
+	return os.CopyFS(dst, src)
+}
diff --git a/internal/testgit/repo_new.go b/internal/testgit/repo_new.go
index 8a71e406..4ae80393 100644
--- a/internal/testgit/repo_new.go
+++ b/internal/testgit/repo_new.go
@@ -32,16 +32,7 @@ func NewRepo(tb testing.TB, opts RepoOptions) *TestRepo {
 	testRepo := &TestRepo{
 		dir:  dir,
 		algo: algo,
-		env: append(os.Environ(),
-			"GIT_CONFIG_GLOBAL=/dev/null",
-			"GIT_CONFIG_SYSTEM=/dev/null",
-			"GIT_AUTHOR_NAME=Test Author",
-			"GIT_AUTHOR_EMAIL=test@example.org",
-			"GIT_COMMITTER_NAME=Test Committer",
-			"GIT_COMMITTER_EMAIL=committer@example.org",
-			"GIT_AUTHOR_DATE=1234567890 +0000",
-			"GIT_COMMITTER_DATE=1234567890 +0000",
-		),
+		env:  defaultEnv(),
 	}
 
 	args := []string{"init", "--object-format=" + algo.String()}
@@ -58,3 +49,16 @@ func NewRepo(tb testing.TB, opts RepoOptions) *TestRepo {
 
 	return testRepo
 }
+
+func defaultEnv() []string {
+	return append(os.Environ(),
+		"GIT_CONFIG_GLOBAL=/dev/null",
+		"GIT_CONFIG_SYSTEM=/dev/null",
+		"GIT_AUTHOR_NAME=Test Author",
+		"GIT_AUTHOR_EMAIL=test@example.org",
+		"GIT_COMMITTER_NAME=Test Committer",
+		"GIT_COMMITTER_EMAIL=committer@example.org",
+		"GIT_AUTHOR_DATE=1234567890 +0000",
+		"GIT_COMMITTER_DATE=1234567890 +0000",
+	)
+}
diff --git a/internal/testgit/repo_properties.go b/internal/testgit/repo_properties.go
index 47123ee8..3a489124 100644
--- a/internal/testgit/repo_properties.go
+++ b/internal/testgit/repo_properties.go
@@ -11,3 +11,8 @@ func (testRepo *TestRepo) Dir() string {
 func (testRepo *TestRepo) Algorithm() objectid.Algorithm {
 	return testRepo.algo
 }
+
+// Env returns a copy of the environment used for git subprocesses.
+func (testRepo *TestRepo) Env() []string {
+	return append([]string(nil), testRepo.env...)
+}
diff --git a/internal/testgit/repo_rev_list.go b/internal/testgit/repo_rev_list.go
new file mode 100644
index 00000000..d3adf5a0
--- /dev/null
+++ b/internal/testgit/repo_rev_list.go
@@ -0,0 +1,37 @@
+package testgit
+
+import (
+	"strings"
+	"testing"
+
+	"codeberg.org/lindenii/furgit/objectid"
+)
+
+// RevList runs "git rev-list" with args and parses one object ID per line.
+func (testRepo *TestRepo) RevList(tb testing.TB, args ...string) []objectid.ObjectID {
+	tb.Helper()
+
+	cmdArgs := make([]string, 0, len(args)+1)
+	cmdArgs = append(cmdArgs, "rev-list")
+	cmdArgs = append(cmdArgs, args...)
+	out := testRepo.Run(tb, cmdArgs...)
+
+	lines := strings.Split(strings.TrimSpace(out), "\n")
+
+	outIDs := make([]objectid.ObjectID, 0, len(lines))
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+
+		id, err := objectid.ParseHex(testRepo.algo, line)
+		if err != nil {
+			tb.Fatalf("parse rev-list oid %q: %v", line, err)
+		}
+
+		outIDs = append(outIDs, id)
+	}
+
+	return outIDs
+}