sql: allow customize column diffing change (#3179)

sql/internal/sqlx/diff.go

@@ -14,6 +14,10 @@ import (
 	"ariga.io/atlas/sql/schema"
 )
 
+// NoChange can be returned by DiffDriver methods
+// to indicate that no change is needed.
+var NoChange = schema.Change(nil)
+
 type (
 	// A Diff provides a generic schema.Differ for diffing schema elements.
 	//
@@ -48,7 +52,7 @@ type (
 		ViewAttrChanged(from, to *schema.View) bool
 
 		// ColumnChange returns the schema changes (if any) for migrating one column to the other.
-		ColumnChange(fromT *schema.Table, from, to *schema.Column) (schema.ChangeKind, error)
+		ColumnChange(fromT *schema.Table, from, to *schema.Column) (schema.Change, error)
 
 		// IndexAttrChanged reports if the index attributes were changed.
 		// For example, an index type or predicate (for partial indexes).
@@ -393,12 +397,8 @@ func (d *Diff) columnDiff(from, to *schema.Table, opts *schema.DiffOptions) ([]s
 		if err != nil {
 			return nil, err
 		}
-		if change != schema.NoChange {
-			all = append(all, &schema.ModifyColumn{
-				From:   c1,
-				To:     c2,
-				Change: change,
-			})
+		if change != NoChange {
+			all = append(all, change)
 		}
 	}
 	// Add columns.

sql/mysql/diff.go

@@ -112,43 +112,50 @@ func (d *diff) TableAttrDiff(from, to *schema.Table) ([]schema.Change, error) {
 }
 
 // ColumnChange returns the schema changes (if any) for migrating one column to the other.
-func (d *diff) ColumnChange(fromT *schema.Table, from, to *schema.Column) (schema.ChangeKind, error) {
+func (d *diff) ColumnChange(fromT *schema.Table, from, to *schema.Column) (schema.Change, error) {
 	change := sqlx.CommentChange(from.Attrs, to.Attrs)
 	if from.Type.Null != to.Type.Null {
 		change |= schema.ChangeNull
 	}
 	changed, err := d.typeChanged(from, to)
 	if err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeType
 	}
 	if changed, err = d.defaultChanged(from, to); err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeDefault
 	}
 	if changed, err = d.generatedChanged(from, to); err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeGenerated
 	}
 	if changed, err = d.columnCharsetChanged(fromT, from, to); err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeCharset
 	}
 	if changed, err = d.columnCollateChanged(fromT, from, to); err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeCollate
 	}
-	return change, nil
+	if change.Is(schema.NoChange) {
+		return sqlx.NoChange, nil
+	}
+	return &schema.ModifyColumn{
+		Change: change,
+		From:   from,
+		To:     to,
+	}, nil
 }
 
 // IsGeneratedIndexName reports if the index name was generated by the database.

sql/postgres/crdb.go

@@ -78,7 +78,7 @@ func (cd *crdbDiff) Normalize(from, to *schema.Table, _ *schema.DiffOptions) err
 	return nil
 }
 
-func (cd *crdbDiff) ColumnChange(fromT *schema.Table, from, to *schema.Column) (schema.ChangeKind, error) {
+func (cd *crdbDiff) ColumnChange(fromT *schema.Table, from, to *schema.Column) (schema.Change, error) {
 	// All serial types in Cockroach are implemented as bigint.
 	// See: https://www.cockroachlabs.com/docs/stable/serial.html#generated-values-for-mode-sql_sequence-and-sql_sequence_cached.
 	for _, c := range []*schema.Column{from, to} {

sql/postgres/diff_oss.go

@@ -76,20 +76,20 @@ func (d *diff) TableAttrDiff(from, to *schema.Table) ([]schema.Change, error) {
 }
 
 // ColumnChange returns the schema changes (if any) for migrating one column to the other.
-func (d *diff) ColumnChange(_ *schema.Table, from, to *schema.Column) (schema.ChangeKind, error) {
+func (d *diff) ColumnChange(_ *schema.Table, from, to *schema.Column) (schema.Change, error) {
 	change := sqlx.CommentChange(from.Attrs, to.Attrs)
 	if from.Type.Null != to.Type.Null {
 		change |= schema.ChangeNull
 	}
 	changed, err := d.typeChanged(from, to)
 	if err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeType
 	}
 	if changed, err = d.defaultChanged(from, to); err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeDefault
@@ -98,12 +98,19 @@ func (d *diff) ColumnChange(_ *schema.Table, from, to *schema.Column) (schema.Ch
 		change |= schema.ChangeAttr
 	}
 	if changed, err = d.generatedChanged(from, to); err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeGenerated
 	}
-	return change, nil
+	if change.Is(schema.NoChange) {
+		return sqlx.NoChange, nil
+	}
+	return &schema.ModifyColumn{
+		Change: change,
+		From:   from,
+		To:     to,
+	}, nil
 }
 
 // defaultChanged reports if the default value of a column was changed.

sql/sqlite/diff.go

@@ -64,14 +64,14 @@ func (d *diff) ViewAttrChanged(_, _ *schema.View) bool {
 
 // ColumnChange returns the schema changes (if any) for migrating one column to the other.
 // Note that column comments are ignored as SQLite does not support it.
-func (d *diff) ColumnChange(_ *schema.Table, from, to *schema.Column) (schema.ChangeKind, error) {
+func (d *diff) ColumnChange(_ *schema.Table, from, to *schema.Column) (schema.Change, error) {
 	var change schema.ChangeKind
 	if from.Type.Null != to.Type.Null {
 		change |= schema.ChangeNull
 	}
 	changed, err := d.typeChanged(from, to)
 	if err != nil {
-		return schema.NoChange, err
+		return sqlx.NoChange, err
 	}
 	if changed {
 		change |= schema.ChangeType
@@ -82,7 +82,14 @@ func (d *diff) ColumnChange(_ *schema.Table, from, to *schema.Column) (schema.Ch
 	if d.generatedChanged(from, to) {
 		change |= schema.ChangeGenerated
 	}
-	return change, nil
+	if change.Is(schema.NoChange) {
+		return sqlx.NoChange, nil
+	}
+	return &schema.ModifyColumn{
+		Change: change,
+		From:   from,
+		To:     to,
+	}, nil
 }
 
 // typeChanged reports if the column type was changed.