From 1772eac120e8d83fcba3de28565a9f55967da4d2 Mon Sep 17 00:00:00 2001
From: Nick Tobey <nick@dolthub.com>
Date: Sat, 18 Jan 2025 02:16:56 -0800
Subject: [PATCH] Don't rewrite enum columns when not necessary.

---
 go/libraries/doltcore/schema/typeinfo/typeinfo.go | 11 +++++++++++
 go/libraries/doltcore/sqle/tables.go              |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/go/libraries/doltcore/schema/typeinfo/typeinfo.go b/go/libraries/doltcore/schema/typeinfo/typeinfo.go
index fea78d8f5d..1b69b45d53 100644
--- a/go/libraries/doltcore/schema/typeinfo/typeinfo.go
+++ b/go/libraries/doltcore/schema/typeinfo/typeinfo.go
@@ -134,6 +134,17 @@ type TypeInfo interface {
 	fmt.Stringer
 }
 
+// RequiresRewrite returns whether or now changing a column type from |old| to |new| requires rewriting table rows.
+func RequiresRewrite(old TypeInfo, new TypeInfo) bool {
+	oldEnum, isOldEnum := old.ToSqlType().(sql.EnumType)
+	newEnum, isNewEnum := new.ToSqlType().(sql.EnumType)
+	if isOldEnum && isNewEnum && oldEnum.IsSubsetOf(newEnum) {
+		return false
+	}
+
+	return true
+}
+
 // FromSqlType takes in a sql.Type and returns the most relevant TypeInfo.
 func FromSqlType(sqlType sql.Type) (TypeInfo, error) {
 	if gmsExtendedType, ok := sqlType.(gmstypes.ExtendedType); ok {
diff --git a/go/libraries/doltcore/sqle/tables.go b/go/libraries/doltcore/sqle/tables.go
index e8fb46ea5d..a73cc933b9 100644
--- a/go/libraries/doltcore/sqle/tables.go
+++ b/go/libraries/doltcore/sqle/tables.go
@@ -1682,7 +1682,7 @@ func (t *AlterableDoltTable) isIncompatibleTypeChange(oldColumn *sql.Column, new
 	if !existingCol.TypeInfo.Equals(newCol.TypeInfo) {
 		if types.IsFormat_DOLT(t.Format()) {
 			// This is overly broad, we could narrow this down a bit
-			return true
+			return typeinfo.RequiresRewrite(existingCol.TypeInfo, newCol.TypeInfo)
 		}
 		if existingCol.Kind != newCol.Kind {
 			return true