From f8692f3bdee512a1f20da1a5e2841dbd56ce4e4d Mon Sep 17 00:00:00 2001
From: Sosuke Suzuki <aosukeke@gmail.com>
Date: Tue, 10 Mar 2020 23:33:33 +0900
Subject: [PATCH] TypeScript: Print dangling comment in empty type parameters
 (#7729)

* Modify to print dangling comment in type parameters

* Add changelog

* Fix changelog

* Modify to support line comment

* Fix changelog

* Change line to hardline
---
 changelog_unreleased/typescript/pr-7729.md    | 13 ++++
 src/language-js/printer-estree.js             | 25 +++++++-
 .../__snapshots__/jsfmt.spec.js.snap          | 60 +++++++++++++++++++
 tests/typescript_comments/type-parameters.ts  | 28 +++++++++
 4 files changed, 125 insertions(+), 1 deletion(-)
 create mode 100644 changelog_unreleased/typescript/pr-7729.md

diff --git a/changelog_unreleased/typescript/pr-7729.md b/changelog_unreleased/typescript/pr-7729.md
new file mode 100644
index 000000000..6a5f7f97d
--- /dev/null
+++ b/changelog_unreleased/typescript/pr-7729.md
@@ -0,0 +1,13 @@
+#### Fix printing of comments in empty type parameters ([#7729](https://github.com/prettier/prettier/pull/7729) by [@sosukesuzuki](https://github.com/sosukesuzuki))
+
+<!-- prettier-ignore -->
+```ts
+// Input
+const a: T</* comment */> = 1;
+
+// Prettier stable
+Error: Comment "comment" was not printed. Please report this error!
+
+// Prettier master
+const a: T</* comment */> = 1;
+```
diff --git a/src/language-js/printer-estree.js b/src/language-js/printer-estree.js
index 8ee3608f1..9fefddb39 100644
--- a/src/language-js/printer-estree.js
+++ b/src/language-js/printer-estree.js
@@ -4638,8 +4638,31 @@ function printTypeParameters(path, options, print, paramsKey) {
           n[paramsKey][0].type !== "TSIndexedAccessType" &&
           n[paramsKey][0].type !== "TSArrayType")));
 
+  function printDanglingCommentsForInline(n) {
+    if (!hasDanglingComments(n)) {
+      return "";
+    }
+    const hasOnlyBlockComments = n.comments.every(
+      handleComments.isBlockComment
+    );
+    const printed = comments.printDanglingComments(
+      path,
+      options,
+      /* sameIndent */ hasOnlyBlockComments
+    );
+    if (hasOnlyBlockComments) {
+      return printed;
+    }
+    return concat([printed, hardline]);
+  }
+
   if (shouldInline) {
-    return concat(["<", join(", ", path.map(print, paramsKey)), ">"]);
+    return concat([
+      "<",
+      join(", ", path.map(print, paramsKey)),
+      printDanglingCommentsForInline(n),
+      ">"
+    ]);
   }
 
   return group(
diff --git a/tests/typescript_comments/__snapshots__/jsfmt.spec.js.snap b/tests/typescript_comments/__snapshots__/jsfmt.spec.js.snap
index d0a344660..1282449f9 100644
--- a/tests/typescript_comments/__snapshots__/jsfmt.spec.js.snap
+++ b/tests/typescript_comments/__snapshots__/jsfmt.spec.js.snap
@@ -663,9 +663,69 @@ printWidth: 80
                                                                                 | printWidth
 =====================================input======================================
 functionName<A /* A comment */>();
+const a: T</* comment */> = 1;
+functionName</* comment */>();
+function foo</* comment */>() {}
+interface Foo {
+ </* comment */>(arg): any;
+}
+type T = </* comment */>(arg) => any;
+
+functionName<
+  A // comment
+>();
+const a: T<
+  // comment
+> = 1;
+functionName<
+  // comment
+>();
+function foo<
+  // comment
+>() {}
+interface Foo {
+ <
+  A// comment
+ >(arg): any;
+}
+type T = <
+  // comment
+>(arg) => any;
 
 =====================================output=====================================
 functionName<A /* A comment */>();
+const a: T</* comment */> = 1;
+functionName</* comment */>();
+function foo</* comment */>() {}
+interface Foo {
+  </* comment */>(arg): any;
+}
+type T = </* comment */>(arg) => any;
+
+functionName<
+  A // comment
+>();
+const a: T<
+  // comment
+> = 1;
+functionName<
+  // comment
+>();
+function foo<
+  // comment
+>() {}
+interface Foo {
+  <
+    A // comment
+  >(
+    arg
+  ): any;
+}
+type T = <
+  // comment
+>(
+  arg
+) => any;
 
 ================================================================================
 `;
diff --git a/tests/typescript_comments/type-parameters.ts b/tests/typescript_comments/type-parameters.ts
index e993143af..42990a4ea 100644
--- a/tests/typescript_comments/type-parameters.ts
+++ b/tests/typescript_comments/type-parameters.ts
@@ -1 +1,29 @@
 functionName<A /* A comment */>();
+const a: T</* comment */> = 1;
+functionName</* comment */>();
+function foo</* comment */>() {}
+interface Foo {
+ </* comment */>(arg): any;
+}
+type T = </* comment */>(arg) => any;
+
+functionName<
+  A // comment
+>();
+const a: T<
+  // comment
+> = 1;
+functionName<
+  // comment
+>();
+function foo<
+  // comment
+>() {}
+interface Foo {
+ <
+  A// comment
+ >(arg): any;
+}
+type T = <
+  // comment
+>(arg) => any;