Fix printing comment for the last operand of union types (#15409)

changelog_unreleased/typescript/15409.md

@@ -0,0 +1,36 @@
+#### Fix printing comment for the last operand of union types (#15409 by @sosukesuzuki)
+
+<!-- prettier-ignore -->
+```tsx
+// Input
+type Foo1 = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+)[]; // Final comment1
+type Foo2 = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+) & Bar; // Final comment2
+
+// Prettier stable
+type Foo1 = (
+  | "thing1" // Comment1
+  | "thing2"
+)[]; // Comment2 // Final comment1
+type Foo2 = (
+  | "thing1" // Comment1
+  | "thing2"
+) & // Comment2
+  Bar; // Final comment2
+
+// Prettier main
+type Foo1 = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+)[]; // Final comment1
+type Foo2 = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+) &
+  Bar; // Final comment2
+```

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

@@ -84,6 +84,7 @@ function handleEndOfLineComment(context) {
     handleVariableDeclaratorComments,
     handleBreakAndContinueStatementComments,
     handleSwitchDefaultCaseComments,
+    handleLastUnionElementInExpression,
   ].some((fn) => fn(context));
 }
 
@@ -887,6 +888,44 @@ function handleSwitchDefaultCaseComments({
   return true;
 }
 
+/**
+ * Handle `Comment2` and `Comment4`.
+ *
+ *   type Foo = (
+ *     | "thing1" // Comment1
+ *     | "thing2" // Comment2
+ *   )[];
+ *
+ *   type Foo = (
+ *     | "thing1" // Comment3
+ *     | "thing2" // Comment4
+ *   ) & Bar;
+ *
+ * @param {CommentContext} context
+ * @returns {boolean}
+ */
+function handleLastUnionElementInExpression({
+  comment,
+  precedingNode,
+  enclosingNode,
+  followingNode,
+}) {
+  if (
+    precedingNode &&
+    (precedingNode.type === "TSUnionType" ||
+      precedingNode.type === "UnionTypeAnnotation") &&
+    (((enclosingNode.type === "TSArrayType" ||
+      enclosingNode.type === "ArrayTypeAnnotation") &&
+      followingNode === undefined) ||
+      enclosingNode.type === "TSIntersectionType" ||
+      enclosingNode.type === "IntersectionTypeAnnotation")
+  ) {
+    addTrailingComment(precedingNode.types.at(-1), comment);
+    return true;
+  }
+  return false;
+}
+
 /**
  * @param {Node} node
  * @returns {boolean}

tests/format/flow/union/__snapshots__/jsfmt.spec.js.snap

@@ -22,6 +22,37 @@ const myValue = (callcallcallcallcallcall(
 ================================================================================
 `;
 
+exports[`comments.js format 1`] = `
+====================================options=====================================
+parsers: ["flow"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+)[]; // Final comment1
+
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+) & Bar; // Final comment2
+
+=====================================output=====================================
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+)[]; // Final comment1
+
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+) &
+  Bar; // Final comment2
+
+================================================================================
+`;
+
 exports[`union.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow/union/comments.js

@@ -0,0 +1,9 @@
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+)[]; // Final comment1
+
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+) & Bar; // Final comment2

tests/format/typescript/union/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,36 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`comments.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+)[]; // Final comment1
+
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+) & Bar; // Final comment2
+
+=====================================output=====================================
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+)[]; // Final comment1
+
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+) &
+  Bar; // Final comment2
+
+================================================================================
+`;
+
 exports[`inlining.ts format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]

tests/format/typescript/union/comments.ts

@@ -0,0 +1,9 @@
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+)[]; // Final comment1
+
+type Foo = (
+  | "thing1" // Comment1
+  | "thing2" // Comment2
+) & Bar; // Final comment2