TypeScript: Keep parentheses around a function called with non-null assertion. (#6136)

CHANGELOG.unreleased.md

@@ -276,6 +276,25 @@ type G = keyof T[];
 type G = (keyof T)[];
 ```
 
+### TypeScript: Keep parentheses around a function called with non-null assertion. ([6136] by [@sosukesuzuki])
+
+Previously, Prettier removes necessary parentheses around a call expression with non-null assertion. It happens when it's return value is called as function.
+
+<!-- prettier-ignore -->
+```ts
+// Input
+const a = (b()!)();
+const b = new (c()!)();
+
+// Output (Prettier stable)
+const a = b()!();
+const b = new c()!();
+
+// Output (prettier master)
+const a = (b()!)();
+const b = new (c()!)();
+```
+
 [#5979]: https://github.com/prettier/prettier/pull/5979
 [#6086]: https://github.com/prettier/prettier/pull/6086
 [#6088]: https://github.com/prettier/prettier/pull/6088
@@ -288,6 +307,7 @@ type G = (keyof T)[];
 [#6129]: https://github.com/prettier/prettier/pull/6129
 [#6130]: https://github.com/prettier/prettier/pull/6130
 [#6131]: https://github.com/prettier/prettier/pull/6131
+[#6136]: https://github.com/prettier/prettier/pull/6136
 [@belochub]: https://github.com/belochub
 [@brainkim]: https://github.com/brainkim
 [@duailibe]: https://github.com/duailibe

src/language-js/needs-parens.js

@@ -717,6 +717,15 @@ function needsParens(path, options) {
         return false;
       }
       return true;
+    case "TSNonNullExpression": {
+      if (
+        node.expression.type !== "Identifier" &&
+        (parent.type === "CallExpression" || parent.type === "NewExpression")
+      ) {
+        return true;
+      }
+      return false;
+    }
   }
 
   return false;

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

@@ -56,6 +56,10 @@ function* g() {
     return (yield * foo())!;
 }
 
+const a = (b()!)();
+const b = c!();
+const c = new (d()!)();
+
 =====================================output=====================================
 (a ? b : c)![tokenKey];
 (a || b)![tokenKey];
@@ -69,5 +73,9 @@ function* g() {
   return (yield* foo())!;
 }
 
+const a = (b()!)();
+const b = c!();
+const c = new (d()!)();
+
 ================================================================================
 `;

tests/typescript_non_null/parens.ts

@@ -9,3 +9,7 @@ async function f() {
 function* g() {
     return (yield * foo())!;
 }
+
+const a = (b()!)();
+const b = c!();
+const c = new (d()!)();