cmd/atlas/migratelint: add support for dir-based change detector (#2042)

cmd/atlas/internal/migratelint/lint.go

@@ -130,7 +130,40 @@ func (d *GitChangeDetector) DetectChanges(ctx context.Context) ([]migrate.File,
 	return files, nil, nil
 }
 
-var _ ChangeDetector = (*GitChangeDetector)(nil)
+var (
+	_ ChangeDetector = (*GitChangeDetector)(nil)
+	_ ChangeDetector = (*DirChangeDetector)(nil)
+)
+
+// A DirChangeDetector implements the ChangeDetector
+// interface by comparing two migration directories.
+type DirChangeDetector struct {
+	// Base and Head are the migration directories to compare.
+	// Base represents the current state, Head the desired state.
+	Base, Head migrate.Dir
+}
+
+// DetectChanges implements migratelint.ChangeDetector.
+func (d DirChangeDetector) DetectChanges(context.Context) ([]migrate.File, []migrate.File, error) {
+	baseS, err := d.Base.Checksum()
+	if err != nil {
+		return nil, nil, err
+	}
+	headS, err := d.Head.Checksum()
+	if err != nil {
+		return nil, nil, err
+	}
+	files, err := d.Head.Files()
+	if err != nil {
+		return nil, nil, err
+	}
+	for i := range headS {
+		if len(baseS)-1 < i || baseS[i] != headS[i] {
+			return files[:i], files[i:], nil
+		}
+	}
+	return files, nil, nil
+}
 
 // latestChange implements the ChangeDetector by selecting the latest N files.
 type latestChange struct {

cmd/atlas/internal/migratelint/lint_test.go

@@ -89,6 +89,25 @@ func TestGitChangeDetector(t *testing.T) {
 	require.Equal(t, "6_new.sql", feat[1].Name())
 }
 
+func TestDirChangeDetector(t *testing.T) {
+	base, head := &migrate.MemDir{}, &migrate.MemDir{}
+	require.NoError(t, base.WriteFile("1.sql", []byte("create table t1 (id int)")))
+	require.NoError(t, head.WriteFile("1.sql", []byte("create table t1 (id int)")))
+	require.NoError(t, base.WriteFile("2.sql", []byte("create table t2 (id int)")))
+	require.NoError(t, head.WriteFile("2.sql", []byte("create table t2 (id int)")))
+
+	baseF, newF, err := migratelint.DirChangeDetector{Base: base, Head: head}.DetectChanges(context.Background())
+	require.NoError(t, err)
+	require.Len(t, baseF, 2)
+	require.Empty(t, newF)
+
+	require.NoError(t, head.WriteFile("3.sql", []byte("create table t3 (id int)")))
+	baseF, newF, err = migratelint.DirChangeDetector{Base: base, Head: head}.DetectChanges(context.Background())
+	require.NoError(t, err)
+	require.Len(t, baseF, 2)
+	require.Len(t, newF, 1)
+}
+
 func TestLatestChanges(t *testing.T) {
 	files := []migrate.File{
 		testFile{name: "1.sql", content: "CREATE TABLE t1 (id INT)"},