Preserve a comment on between decorator and modified parameter property (#16574)

changelog_unreleased/typescript/16574.md

@@ -0,0 +1,35 @@
+#### Preserve a comment on between decorator and modified parameter property (#16574 by @sosukesuzuki)
+
+The current version of Prettier unexpectedly moves a line comment between a parameter property modified by `readonly`, `private`, `public`, etc and a decorator. This output results in invalid TypeScript code.
+
+This change ensures that the original format is preserved.
+
+<!-- prettier-ignore -->
+```ts
+// Input
+class Foo {
+  constructor(
+    @decorator
+    // comment
+    readonly foo,
+  ) {}
+}
+
+// Output (stable)
+class Foo {
+  constructor(
+    @decorator
+    readonly // comment
+    foo,
+  ) {}
+}
+
+// Output (main)
+class Foo {
+  constructor(
+    @decorator
+    // comment
+    readonly foo,
+  ) {}
+}
+```

src/language-js/comments/handle-comments.js

@@ -495,6 +495,7 @@ const propertyLikeNodeTypes = new Set([
   "ClassAccessorProperty",
   "AccessorProperty",
   "TSAbstractAccessorProperty",
+  "TSParameterProperty",
 ]);
 function handleMethodNameComments({
   comment,

tests/format/typescript/comments/16065.ts

@@ -0,0 +1,11 @@
+class Foo {
+  constructor(
+    @decorator1
+    // comment1
+    readonly baz1: string,
+
+    @decorator2
+    // comment2
+    private baz2: string,
+  ) {}
+}

tests/format/typescript/comments/__snapshots__/format.test.js.snap

@@ -122,6 +122,40 @@ const [
 ================================================================================
 `;
 
+exports[`16065.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+class Foo {
+  constructor(
+    @decorator1
+    // comment1
+    readonly baz1: string,
+
+    @decorator2
+    // comment2
+    private baz2: string,
+  ) {}
+}
+
+=====================================output=====================================
+class Foo {
+  constructor(
+    @decorator1
+    // comment1
+    readonly baz1: string,
+
+    @decorator2
+    // comment2
+    private baz2: string,
+  ) {}
+}
+
+================================================================================
+`;
+
 exports[`abstract_class.ts format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]