Navigate to snapshots from the transcript

internal/git/changes.go

@@ -18,20 +18,27 @@ var statuses = map[byte]api.FileChangeStatus{
 }
 
 func Changes(dir, defaultBranch, since string) (api.TaskChanges, error) {
+	tree, err := Snapshot(dir)
+	if err != nil {
+		return api.TaskChanges{}, err
+	}
+	return Compare(dir, defaultBranch, "HEAD", tree, since)
+}
+
+func Parent(dir, commit string) (string, error) {
+	return run(dir, "rev-parse", "--verify", commit+"^")
+}
+
+func Compare(dir, defaultBranch, head, tree, since string) (api.TaskChanges, error) {
 	base := since
 	if base == "" {
-		mb, err := run(dir, "merge-base", "HEAD", defaultBranch)
+		mb, err := run(dir, "merge-base", head, defaultBranch)
 		if err != nil {
 			return api.TaskChanges{}, err
 		}
 		base = mb
 	}
 
-	tree, err := Snapshot(dir)
-	if err != nil {
-		return api.TaskChanges{}, err
-	}
-
 	files, err := stats(dir, base, tree)
 	if err != nil {
 		return api.TaskChanges{}, err

internal/git/changes_test.go

@@ -142,3 +142,87 @@ func TestChanges(t *testing.T) {
 		t.Fatalf("CommitAll on a clean tree: %q %v", again, err)
 	}
 }
+
+func TestCompareSnapshots(t *testing.T) {
+	dir := t.TempDir()
+	git := func(args ...string) string {
+		t.Helper()
+		out, err := run(dir, args...)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return out
+	}
+	write := func(name, content string) {
+		t.Helper()
+		err := os.WriteFile(filepath.Join(dir, name), []byte(content), 0o644)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	snap := func(n int) (string, string) {
+		t.Helper()
+		tree, err := Snapshot(dir)
+		if err != nil {
+			t.Fatal(err)
+		}
+		commit, err := CommitSnapshot(dir, tree, SnapshotRef("t1", n), "snap", nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return commit, tree
+	}
+	paths := func(c api.TaskChanges) string {
+		names := []string{}
+		for _, f := range c.Files {
+			names = append(names, f.Path)
+		}
+		return strings.Join(names, ",")
+	}
+
+	git("init", "--quiet", "--initial-branch=main")
+	git("config", "user.email", "test@example.com")
+	git("config", "user.name", "test")
+	write("a.txt", "a\n")
+	git("add", ".")
+	git("commit", "--quiet", "-m", "base")
+	git("switch", "--quiet", "-c", "task")
+
+	write("b.txt", "b\n")
+	commit1, tree1 := snap(1)
+	write("c.txt", "c\n")
+	commit2, tree2 := snap(2)
+	write("d.txt", "d\n")
+
+	sinceMain, err := Compare(dir, "main", commit2, tree2, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := paths(sinceMain); got != "b.txt,c.txt" {
+		t.Fatalf("snapshot 2 since main: got %s", got)
+	}
+
+	step, err := Compare(dir, "main", commit2, tree2, tree1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := paths(step); got != "c.txt" {
+		t.Fatalf("snapshot 2 step: got %s", got)
+	}
+	patch, err := FileDiff(dir, step.Base, step.Tree, "c.txt", "")
+	if err != nil || !strings.Contains(patch, "+c") {
+		t.Fatalf("snapshot 2 step patch: %q %v", patch, err)
+	}
+
+	parent, err := Parent(dir, commit1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	first, err := Compare(dir, "main", commit1, tree1, parent)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := paths(first); got != "b.txt" {
+		t.Fatalf("snapshot 1 step: got %s", got)
+	}
+}