TypeScript: Prefer leading comment when there is a comment on after "?" in conditional types (#8557)

* Fix #8555

* Add changelog

changelog_unreleased/javascript/pr-8557.md

@@ -0,0 +1,22 @@
+#### Prefer leading comment when there is a comment on after "?" in conditional types ([#8557](https://github.com/prettier/prettier/pull/8557) by [@sosukesuzuki](https://github.com/sosukesuzuki))
+
+<!-- prettier-ignore -->
+```ts
+// Input
+type A = B extends T
+  ? // comment
+    foo
+  : bar;
+
+// Prettier stable
+type A = B extends T // comment
+  ? foo
+  : bar;
+
+// Prettier master
+type A = B extends T
+  ? // comment
+    foo
+  : bar;
+
+```

src/language-js/comments.js

@@ -407,7 +407,8 @@ function handleConditionalExpressionComments(
   if (
     (!precedingNode || !isSameLineAsPrecedingNode) &&
     enclosingNode &&
-    enclosingNode.type === "ConditionalExpression" &&
+    (enclosingNode.type === "ConditionalExpression" ||
+      enclosingNode.type === "TSConditionalType") &&
     followingNode
   ) {
     addLeadingComment(followingNode, comment);

tests/typescript/conditional-types/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,25 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`comments.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type A = B extends T
+  ? // comment
+    foo
+  : bar;
+
+=====================================output=====================================
+type A = B extends T
+  ? // comment
+    foo
+  : bar;
+
+================================================================================
+`;
+
 exports[`conditonal-types.ts format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]

tests/typescript/conditional-types/comments.ts

@@ -0,0 +1,4 @@
+type A = B extends T
+  ? // comment
+    foo
+  : bar;