dialect/sql/schema: file based type store (#2644)

* dialect/sql/schema: file based type store

This PR adds support for a file based type storage when using versioned migrations. The file called `.ent_types` is written to the migration directory alongside the migration files and will be kept in sync for every migration file generation run.

In order to not break existing code, where the type storage might differ for different deployment, global unique ID mut be enabled by using a new option. This will also be raised as an error to the user when attempting to use versioned migrations and global unique ID.

Documentation will be added to this PR once feedback on the code is gathered.

* apply CR

* fix tests

* change format of types file to exclude it from atlas.sum file

* docs and drift test

* apply CR

dialect/sql/schema/atlas.go

@@ -9,6 +9,8 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"io/fs"
+	"io/ioutil"
 	"sort"
 	"strings"
 
@@ -271,16 +273,32 @@ func WithSumFile() MigrateOption {
 	}
 }
 
+// WithUniversalID instructs atlas to use a file based type store when
+// global unique ids are enabled. For more information see the setupAtlas method on Migrate.
+//
+// ATTENTION:
+// The file based PK range store is not backward compatible, since the allocated ranges were computed
+// dynamically when computing the diff between a deployed database and the current schema. In cases where there
+// exist multiple deployments, the allocated ranges for the same type might be different from each other,
+// depending on when the deployment took part.
+func WithUniversalID() MigrateOption {
+	return func(m *Migrate) {
+		m.universalID = true
+		m.atlas.typeStoreConsent = true
+	}
+}
+
 type (
 	// atlasOptions describes the options for atlas.
 	atlasOptions struct {
-		enabled bool
-		diff    []DiffHook
-		apply   []ApplyHook
-		skip    ChangeKind
-		dir     migrate.Dir
-		fmt     migrate.Formatter
-		genSum  bool
+		enabled          bool
+		diff             []DiffHook
+		apply            []ApplyHook
+		skip             ChangeKind
+		dir              migrate.Dir
+		fmt              migrate.Formatter
+		genSum           bool
+		typeStoreConsent bool
 	}
 
 	// atBuilder must be implemented by the different drivers in
@@ -293,9 +311,12 @@ type (
 		atIncrementC(*schema.Table, *schema.Column)
 		atIncrementT(*schema.Table, int64)
 		atIndex(*Index, *schema.Table, *schema.Index) error
+		atTypeRangeSQL(t ...string) string
 	}
 )
 
+var errConsent = errors.New("sql/schema: use WithUniversalID() instead of WithGlobalUniqueID(true) when using WithDir(): https://entgo.io/docs/migrate#universal-ids")
+
 func (m *Migrate) setupAtlas() error {
 	// Using one of the Atlas options, opt-in to Atlas migration.
 	if !m.atlas.enabled && (m.atlas.skip != NoChange || len(m.atlas.diff) > 0 || len(m.atlas.apply) > 0) || m.atlas.dir != nil {
@@ -326,6 +347,16 @@ func (m *Migrate) setupAtlas() error {
 	if m.atlas.dir != nil && m.atlas.fmt == nil {
 		m.atlas.fmt = sqltool.GolangMigrateFormatter
 	}
+	if m.universalID && m.atlas.dir != nil {
+		// If global unique ids and a migration directory is given, enable the file based type store for pk ranges.
+		m.typeStore = &dirTypeStore{dir: m.atlas.dir}
+		// To guard the user against a possible bug due to backward incompatibility, the file based type store must
+		// be enabled by an option. For more information see the comment of WithUniversalID function.
+		if !m.atlas.typeStoreConsent {
+			return errConsent
+		}
+		m.atlas.diff = append(m.atlas.diff, m.ensureTypeTable)
+	}
 	return nil
 }
 
@@ -537,6 +568,54 @@ func (m *Migrate) aIndexes(b atBuilder, t1 *Table, t2 *schema.Table) error {
 	return nil
 }
 
+func (m *Migrate) ensureTypeTable(next Differ) Differ {
+	return DiffFunc(func(current, desired *schema.Schema) ([]schema.Change, error) {
+		// If there is a types table but no types file yet, the user most likely
+		// switched from online migration to migration files.
+		if len(m.dbTypeRanges) == 0 {
+			var (
+				at = schema.NewTable(TypeTable)
+				et = NewTable(TypeTable).
+					AddPrimary(&Column{Name: "id", Type: field.TypeUint, Increment: true}).
+					AddColumn(&Column{Name: "type", Type: field.TypeString, Unique: true})
+			)
+			m.atTable(et, at)
+			if err := m.aColumns(m, et, at); err != nil {
+				return nil, err
+			}
+			if err := m.aIndexes(m, et, at); err != nil {
+				return nil, err
+			}
+			desired.Tables = append(desired.Tables, at)
+		}
+		// If there is a drift between the types stored in the database and the ones stored in the file,
+		// stop diffing, as this is potentially destructive. This will most likely happen on the first diffing
+		// after moving from online-migration to versioned migrations if the "old" ent types are not in sync with
+		// the deterministic ones computed by the new engine.
+		if len(m.dbTypeRanges) > 0 && len(m.fileTypeRanges) > 0 && !equal(m.fileTypeRanges, m.dbTypeRanges) {
+			return nil, fmt.Errorf(
+				"type allocation range drift detected: %v <> %v: see %s for more information",
+				m.dbTypeRanges, m.fileTypeRanges,
+				"https://entgo.io/docs/versioned-migrations#moving-from-auto-migration-to-versioned-migrations",
+			)
+		}
+		changes, err := next.Diff(current, desired)
+		if err != nil {
+			return nil, err
+		}
+		if len(m.dbTypeRanges) > 0 && len(m.fileTypeRanges) == 0 {
+			// Override the types file created in the diff process with the "old" allocated types ranges.
+			if err := m.typeStore.(*dirTypeStore).save(m.dbTypeRanges); err != nil {
+				return nil, err
+			}
+			// Change the type range allocations since they will be added to the migration files when
+			// writing the migration plan to migration files.
+			m.typeRanges = m.dbTypeRanges
+		}
+		return changes, nil
+	})
+}
+
 func setAtChecks(t1 *Table, t2 *schema.Table) {
 	if check := t1.Annotation.Check; check != "" {
 		t2.AddChecks(&schema.Check{
@@ -574,3 +653,62 @@ func descIndexes(idx *Index) map[string]bool {
 	}
 	return descs
 }
+
+const entTypes = ".ent_types"
+
+// dirTypeStore stores and read pk information from a text file stored alongside generated versioned migrations.
+// This behaviour is enabled automatically when using versioned migrations.
+type dirTypeStore struct {
+	dir migrate.Dir
+}
+
+const atlasDirective = "atlas:sum ignore\n"
+
+// load the types from the types file.
+func (s *dirTypeStore) load(context.Context, dialect.ExecQuerier) ([]string, error) {
+	f, err := s.dir.Open(entTypes)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return nil, fmt.Errorf("reading types file: %w", err)
+	}
+	if errors.Is(err, fs.ErrNotExist) {
+		return nil, nil
+	}
+	defer f.Close()
+	c, err := ioutil.ReadAll(f)
+	if err != nil {
+		return nil, fmt.Errorf("reading types file: %w", err)
+	}
+	return strings.Split(strings.TrimPrefix(string(c), atlasDirective), ","), nil
+}
+
+// add a new type entry to the types file.
+func (s *dirTypeStore) add(ctx context.Context, conn dialect.ExecQuerier, t string) error {
+	ts, err := s.load(ctx, conn)
+	if err != nil {
+		return fmt.Errorf("adding type %q: %w", t, err)
+	}
+	return s.save(append(ts, t))
+}
+
+// save takes the given allocation range and writes them to the types file.
+// The types file will be overridden.
+func (s *dirTypeStore) save(ts []string) error {
+	if err := s.dir.WriteFile(entTypes, []byte(atlasDirective+strings.Join(ts, ","))); err != nil {
+		return fmt.Errorf("writing types file: %w", err)
+	}
+	return nil
+}
+
+var _ typeStore = (*dirTypeStore)(nil)
+
+func equal(s1, s2 []string) bool {
+	if len(s1) != len(s2) {
+		return false
+	}
+	for i := range s1 {
+		if s1[i] != s2[i] {
+			return false
+		}
+	}
+	return true
+}