From 6d59d2fe60fd7d1b7c76500998497e217cb7a3bf Mon Sep 17 00:00:00 2001
From: Matthew Gaudet <mgaudet@mozilla.com>
Date: Tue, 7 Jul 2020 18:53:04 +0000
Subject: [PATCH] Bug 1642476 - Correctly name anonymous private functions
 bound to private fields. r=jorendorff

Differential Revision: https://phabricator.services.mozilla.com/D77930
---
 js/src/tests/non262/PrivateName/names.js | 31 ++++++++++++++++++++++++
 js/src/vm/JSFunction.cpp                 | 16 +++++++++---
 2 files changed, 44 insertions(+), 3 deletions(-)
 create mode 100644 js/src/tests/non262/PrivateName/names.js

diff --git a/js/src/tests/non262/PrivateName/names.js b/js/src/tests/non262/PrivateName/names.js
new file mode 100644
index 0000000000000..e44fc5935b9df
--- /dev/null
+++ b/js/src/tests/non262/PrivateName/names.js
@@ -0,0 +1,31 @@
+// |reftest| skip-if(!xulRuntime.shell) shell-option(--enable-private-fields)
+
+var C = class {
+  static #field = () => 'Test262';
+  static field = () => 'Test262';
+  #instance = () => 'Test262';
+  instance = () => 'Test262';
+
+  static accessPrivateField() {
+    return this.#field;
+  }
+
+  accessPrivateInstanceField() {
+    return this.#instance;
+  }
+
+  static accessField() {
+    return this.field;
+  }
+
+  accessInstanceField() {
+    return this.instance;
+  }
+}
+assertEq(C.accessPrivateField().name, '#field')
+assertEq(C.accessField().name, 'field');
+var c = new C;
+assertEq(c.accessPrivateInstanceField().name, '#instance');
+assertEq(c.accessInstanceField().name, 'instance');
+
+if (typeof reportCompare === 'function') reportCompare(0, 0);
diff --git a/js/src/vm/JSFunction.cpp b/js/src/vm/JSFunction.cpp
index ef1b9bb717eb7..ca33362c478b3 100644
--- a/js/src/vm/JSFunction.cpp
+++ b/js/src/vm/JSFunction.cpp
@@ -2362,9 +2362,19 @@ static JSAtom* SymbolToFunctionName(JSContext* cx, JS::Symbol* symbol,
 
   // Step 4.b.
   if (desc) {
-    // Step 4.c.
-    if (!sb.append('[') || !sb.append(desc) || !sb.append(']')) {
-      return nullptr;
+    // Note: Private symbols are wedged in, as implementation wise they're
+    // PrivateNameSymbols with a the source level name as a description
+    // i.e. obj.#f desugars to obj.[PrivateNameSymbol("#f")], however
+    // they don't use the symbol naming, but rather property naming.
+    if (symbol->isPrivateName()) {
+      if (!sb.append(desc)) {
+        return nullptr;
+      }
+    } else {
+      // Step 4.c.
+      if (!sb.append('[') || !sb.append(desc) || !sb.append(']')) {
+        return nullptr;
+      }
     }
   }
   return sb.finishAtom();