Inconsistent comment placement in nested unions vs unions in intersections #18778
Description
Prettier 3.8.1
Playground link
--parser typescriptInput:
type UnionInIntersection = (
| "thing1" // Comment1
| "thing2" // Comment2
) & Bar; // Final comment2
type NestedUnion = (
| "thing1" // Comment1
| "thing2" // Comment2
) | Bar; // Final comment2
type UnionInIntersection2 =
(
A | B // comment 1
) & (
// comment2
A | B
)
type NestedUnion2 =
(
A | B // comment 1
) | (
// comment2
A | B
)Output:
type UnionInIntersection = (
| "thing1" // Comment1
| "thing2" // Comment2
) &
Bar; // Final comment2
type NestedUnion =
| (
| "thing1" // Comment1
| "thing2"
) // Comment2
| Bar; // Final comment2
type UnionInIntersection2 = (
| A
| B // comment 1
) &
// comment2
(A | B);
type NestedUnion2 =
| (A | B) // comment 1
// comment2
| (A | B);Expected output:
type UnionInIntersection = (
| "thing1" // Comment1
| "thing2" // Comment2
) &
Bar; // Final comment2
type NestedUnion = (
| "thing1" // Comment1
| "thing2" // Comment2
) |
Bar; // Final comment2
type UnionInIntersection2 = (
| A
| B // comment 1
) &
// comment2
(A | B);
type NestedUnion2 = (
| A
| B // comment 1
) |
// comment2
(A | B);Why?
The current output shows inconsistent comment handling between union-in-intersection and union-in-union cases:
-
UnionInIntersection- Comments stay on their original lines:type UnionInIntersection = ( | "thing1" // Comment1 | "thing2" // Comment2 ) & Bar;
-
NestedUnion- Comments get repositioned, with// Comment2moved outside the parentheses:type NestedUnion = | ( | "thing1" // Comment1 | "thing2" ) // Comment2 | Bar;
This inconsistency is problematic because:
- Comment semantics change:
// Comment2was originally associated with"thing2", but after formatting it appears to comment on the entire parenthesized group - Developer intent is lost: Comments are placed deliberately; reformatting should preserve their associations
The expected output keeps the parenthesized union structure intact with comments in their original positions, matching the behavior of UnionInIntersection.