fix: Unnecessary migrations for fulltext indices

Fixes typeorm#6633 (see issue for root cause explanation)

src/schema-builder/RdbmsSchemaBuilder.ts

@@ -277,7 +277,8 @@ export class RdbmsSchemaBuilder implements SchemaBuilder {
                         if (indexMetadata.isSpatial !== tableIndex.isSpatial)
                             return true;
 
-                        if (indexMetadata.isFulltext !== tableIndex.isFulltext)
+                        // Only MySQL supports fulltext indices
+                        if (this.connection.driver instanceof MysqlDriver && indexMetadata.isFulltext !== tableIndex.isFulltext)
                             return true;
 
                         if (indexMetadata.columns.length !== tableIndex.columnNames.length)

test/github-issues/6633/entity/Test.ts

@@ -0,0 +1,11 @@
+import { Entity, PrimaryColumn, Index, Column } from "../../../../src";
+
+@Entity()
+export class Test {
+    @PrimaryColumn()
+    id: number;
+
+    @Index("description_index", { fulltext: true })
+    @Column()
+    description: string;
+}

test/github-issues/6633/issue-6633.ts

@@ -0,0 +1,29 @@
+import "reflect-metadata";
+import { expect } from "chai";
+import { Connection } from "../../../src";
+import { closeTestingConnections, createTestingConnections, reloadTestingDatabases } from "../../utils/test-utils";
+import { Post } from "../4440/entity/Post";
+
+describe.only("github issues > #6633 Fulltext indices continually dropped & re-created", () => {
+
+    let connections: Connection[];
+    before(async () => {
+        connections = await createTestingConnections({
+            entities: [Post],
+            schemaCreate: true,
+            dropSchema: true
+        });
+    });
+    beforeEach(() => reloadTestingDatabases(connections));
+    after(() => closeTestingConnections(connections));
+
+    it("should not create migrations for fulltext indices", () =>
+        Promise.all(connections.map(async (connection) => {
+                const sqlInMemory = await connection.driver.createSchemaBuilder().log();
+
+                expect(sqlInMemory.upQueries).to.eql([]);
+                expect(sqlInMemory.downQueries).to.eql([]);
+            }
+        ))
+    );
+});