From b0315b81c7d7fea72a9c24f0fb648d48e43ca1a6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=B2=20Ribaudo?= <nicolo.ribaudo@gmail.com>
Date: Sat, 21 Mar 2020 20:53:38 +0100
Subject: [PATCH] Fix logic to insert parens in return statements with comments
 (#11306)

---
 packages/babel-generator/src/printer.js       | 49 ++++++++++++++++---
 .../test/fixtures/regression/11304/input.js   |  7 +++
 .../fixtures/regression/11304/options.json    |  3 ++
 .../test/fixtures/regression/11304/output.js  |  2 +
 4 files changed, 54 insertions(+), 7 deletions(-)
 create mode 100644 packages/babel-generator/test/fixtures/regression/11304/input.js
 create mode 100644 packages/babel-generator/test/fixtures/regression/11304/options.json
 create mode 100644 packages/babel-generator/test/fixtures/regression/11304/output.js

diff --git a/packages/babel-generator/src/printer.js b/packages/babel-generator/src/printer.js
index bb6aeb9967..2403fd9936 100644
--- a/packages/babel-generator/src/printer.js
+++ b/packages/babel-generator/src/printer.js
@@ -249,22 +249,57 @@ export default class Printer {
     // see startTerminatorless() instance method
     const parenPushNewlineState = this._parenPushNewlineState;
     if (!parenPushNewlineState) return;
-    this._parenPushNewlineState = null;
+
+    // This function does two things:
+    // - If needed, prints a parenthesis
+    // - If the currently printed string removes the need for the paren,
+    //   it resets the _parenPushNewlineState field.
+    //   Almost everything removes the need for a paren, except for
+    //   comments and whitespaces.
 
     let i;
     for (i = 0; i < str.length && str[i] === " "; i++) continue;
-    if (i === str.length) return;
+    if (i === str.length) {
+      // Whitespaces only, the parentheses might still be needed.
+      return;
+    }
 
     // Check for newline or comment.
     const cha = str[i];
     if (cha !== "\n") {
-      if (cha !== "/") return;
-      if (i + 1 === str.length) return;
+      if (
+        // This is not a comment (it doesn't start with /)
+        cha !== "/" ||
+        // This is not a comment (it's a / operator)
+        i + 1 === str.length
+      ) {
+        // After a normal token, the parentheses aren't needed anymore
+        this._parenPushNewlineState = null;
+        return;
+      }
+
       const chaPost = str[i + 1];
-      if (chaPost !== "/" && chaPost !== "*") return;
-      // We don't print newlines aroung /*#__PURE__*/ annotations
-      if (PURE_ANNOTATION_RE.test(str.slice(i + 2, str.length - 2))) return;
+
+      if (chaPost === "*") {
+        // This is a block comment
+
+        if (PURE_ANNOTATION_RE.test(str.slice(i + 2, str.length - 2))) {
+          // We avoid printing newlines after #__PURE__ comments (we treat
+          // then as unary operators), but we must keep the old
+          // parenPushNewlineState because, if a newline was forbidden, it is
+          // still forbidden after the comment.
+          return;
+        }
+
+        // NOTE: code flow continues from here to after these if/elses
+      } else if (chaPost !== "/") {
+        // This is neither a block comment, nor a line comment.
+        // After a normal token, the parentheses aren't needed anymore
+        this._parenPushNewlineState = null;
+        return;
+      }
     }
+
     this.token("(");
     this.indent();
     parenPushNewlineState.printed = true;
diff --git a/packages/babel-generator/test/fixtures/regression/11304/input.js b/packages/babel-generator/test/fixtures/regression/11304/input.js
new file mode 100644
index 0000000000..f195ee2d52
--- /dev/null
+++ b/packages/babel-generator/test/fixtures/regression/11304/input.js
@@ -0,0 +1,7 @@
+function f() {
+  return (
+    /*#__PURE__*/
+    //test
+    0
+  );
+}
diff --git a/packages/babel-generator/test/fixtures/regression/11304/options.json b/packages/babel-generator/test/fixtures/regression/11304/options.json
new file mode 100644
index 0000000000..eb4e948bfa
--- /dev/null
+++ b/packages/babel-generator/test/fixtures/regression/11304/options.json
@@ -0,0 +1,3 @@
+{
+  "compact": true
+}
diff --git a/packages/babel-generator/test/fixtures/regression/11304/output.js b/packages/babel-generator/test/fixtures/regression/11304/output.js
new file mode 100644
index 0000000000..108feca555
--- /dev/null
+++ b/packages/babel-generator/test/fixtures/regression/11304/output.js
@@ -0,0 +1,2 @@
+function f(){return/*#__PURE__*/ (//test
+0);}
\ No newline at end of file