TypeScript: Keep semi for a class property before index signatu… (#6728)

* Modify to add semi to prop before TSIndexSignature

Co-Authored-By: Simon Lydell <simon.lydell@gmail.com>

CHANGELOG.unreleased.md

@@ -1269,6 +1269,31 @@ new Map([
 ]);
 ```
 
+#### TypeScript: Keep semi for a class property before index signature when no-semi is enabled ([#6728] by [@sosukesuzuki])
+
+Attempting to format Prettier’s output again used to result in a syntax error.
+
+<!-- prettier-ignore -->
+```ts
+// Input
+export class User {
+  id: number = 2;
+  [key: string]: any
+}
+
+// Output (Prettier stable)
+export class User {
+  id: number = 2
+  [key: string]: any
+}
+
+// Output (Prettier master)
+export class User {
+  id: number = 2;
+  [key: string]: any
+}
+```
+
 [#5682]: https://github.com/prettier/prettier/pull/5682
 [#6657]: https://github.com/prettier/prettier/pull/6657
 [#5910]: https://github.com/prettier/prettier/pull/5910
@@ -1311,6 +1336,7 @@ new Map([
 [#6673]: https://github.com/prettier/prettier/pull/6673
 [#6695]: https://github.com/prettier/prettier/pull/6695
 [#6694]: https://github.com/prettier/prettier/pull/6694
+[#6728]: https://github.com/prettier/prettier/pull/6728
 [@brainkim]: https://github.com/brainkim
 [@duailibe]: https://github.com/duailibe
 [@gavinjoyce]: https://github.com/gavinjoyce

src/language-js/utils.js

@@ -536,7 +536,8 @@ function classChildNeedsASIProtection(node) {
       }
       return false;
     }
-
+    case "TSIndexSignature":
+      return true;
     default:
       /* istanbul ignore next */
       return false;

tests/typescript_semi/__snapshots__/jsfmt.spec.js.snap

@@ -12,11 +12,21 @@ export class Mutation {
   private delete: NQuad[];
 }
 
+class Foo {
+  prop1 = 0;
+  [key: string]: any;
+}
+
 =====================================output=====================================
 export class Mutation {
   private set: NQuad[]
   private delete: NQuad[]
 }
 
+class Foo {
+  prop1 = 0;
+  [key: string]: any
+}
+
 ================================================================================
 `;

tests/typescript_semi/no-semi.ts

@@ -2,3 +2,8 @@ export class Mutation {
   private set: NQuad[];
   private delete: NQuad[];
 }
+
+class Foo {
+  prop1 = 0;
+  [key: string]: any;
+}