From 156b608d48900b9489bd31aff03189a6c18f9040 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=B2=20Ribaudo?= <nicolo.ribaudo@gmail.com>
Date: Mon, 7 Nov 2022 17:50:59 +0100
Subject: [PATCH] Falback to printing inner comments as trailing (#15144)

Fixes https://github.com/babel/babel/issues/15138#issuecomment-1304570362
---
 packages/babel-generator/src/printer.ts       | 31 ++++++++++++-----
 .../types-with-comments-retainLines/output.js |  4 +--
 packages/babel-generator/test/index.js        | 34 +++++++++++++++++++
 .../fixtures/enum/mix-references/output.js    |  2 +-
 4 files changed, 59 insertions(+), 12 deletions(-)

diff --git a/packages/babel-generator/src/printer.ts b/packages/babel-generator/src/printer.ts
index 9a11289bad77..401e19294d4f 100644
--- a/packages/babel-generator/src/printer.ts
+++ b/packages/babel-generator/src/printer.ts
@@ -787,15 +787,28 @@ class Printer {
   }
 
   _printTrailingComments(node: t.Node, parent?: t.Node, lineOffset?: number) {
-    const comments = node.trailingComments;
-    if (!comments?.length) return;
-    this._printComments(
-      COMMENT_TYPE.TRAILING,
-      comments,
-      node,
-      parent,
-      lineOffset,
-    );
+    const { innerComments, trailingComments } = node;
+    // We print inner comments here, so that if for some reason they couldn't
+    // be printed in earlier locations they are still printed *somehwere*,
+    // even if at the end of the node.
+    if (innerComments?.length) {
+      this._printComments(
+        COMMENT_TYPE.TRAILING,
+        innerComments,
+        node,
+        parent,
+        lineOffset,
+      );
+    }
+    if (trailingComments?.length) {
+      this._printComments(
+        COMMENT_TYPE.TRAILING,
+        trailingComments,
+        node,
+        parent,
+        lineOffset,
+      );
+    }
   }
 
   _printLeadingComments(node: t.Node, parent: t.Node) {
diff --git a/packages/babel-generator/test/fixtures/typescript/types-with-comments-retainLines/output.js b/packages/babel-generator/test/fixtures/typescript/types-with-comments-retainLines/output.js
index 1238e16f7699..7647b84b9eda 100644
--- a/packages/babel-generator/test/fixtures/typescript/types-with-comments-retainLines/output.js
+++ b/packages/babel-generator/test/fixtures/typescript/types-with-comments-retainLines/output.js
@@ -6,8 +6,8 @@ C /* 2 */[
 
 type T2 = U.
 /* 1 */
-C /* 2 */[];
-
+C /* 2 */[]
+/* 3 */;
 
 
 type T3 = U.
diff --git a/packages/babel-generator/test/index.js b/packages/babel-generator/test/index.js
index 68e043eb7a70..913325f21df5 100644
--- a/packages/babel-generator/test/index.js
+++ b/packages/babel-generator/test/index.js
@@ -1133,6 +1133,40 @@ describe("programmatic generation", function () {
       expect(output).toBe("for ((let)[x];;);");
     });
   });
+
+  describe("should print inner comments even if there are no suitable inner locations", () => {
+    it("atomic node", () => {
+      const id = t.identifier("foo");
+      id.innerComments = [{ type: "CommentBlock", value: "foo" }];
+      expect(generate(id).code).toMatchInlineSnapshot(`"foo /*foo*/"`);
+    });
+
+    it("node without inner locations", () => {
+      const expr = t.binaryExpression(
+        "+",
+        t.numericLiteral(1),
+        t.numericLiteral(2),
+      );
+      expr.innerComments = [{ type: "CommentBlock", value: "foo" }];
+      expect(generate(expr).code).toMatchInlineSnapshot(`"1 + 2 /*foo*/"`);
+    });
+
+    it("comment skipped because of newlines", () => {
+      const arrow = t.arrowFunctionExpression(
+        [t.identifier("x"), t.identifier("y")],
+        t.identifier("z"),
+      );
+      arrow.innerComments = [
+        { type: "CommentBlock", value: "foo" },
+        { type: "CommentBlock", value: "new\nline" },
+      ];
+      expect(generate(arrow).code).toMatchInlineSnapshot(`
+        "(x, y) /*foo*/ => z
+        /*new
+        line*/"
+      `);
+    });
+  });
 });
 
 describe("CodeGenerator", function () {
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/enum/mix-references/output.js b/packages/babel-plugin-transform-typescript/test/fixtures/enum/mix-references/output.js
index 551584e44474..1f38322e0d4c 100644
--- a/packages/babel-plugin-transform-typescript/test/fixtures/enum/mix-references/output.js
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/enum/mix-references/output.js
@@ -18,7 +18,7 @@ var Baz;
   Baz[Baz["b"] = 1] = "b";
   Baz[Baz["x"] = Baz.a.toString()] = "x";
 })(Baz || (Baz = {}));
-var A;
+var A; // a refers to A.a
 (function (A) {
   A[A["a"] = 0] = "a";
   A[A["b"] = (() => {