Bug 1362154: Part 2: Avoid rooting hazard in CheckPatternSyntax r=mga…

…udet

In debug, CheckPatternSyntax holds an unrooted RegExpShared across a call to the regexp parser. This is the only remaining obstacle to allocating GC things while parsing regexps.

Differential Revision: https://phabricator.services.mozilla.com/D76034

js/src/builtin/RegExp.cpp

@@ -209,7 +209,8 @@ static RegExpShared* CheckPatternSyntax(JSContext* cx, HandleAtom pattern,
   // If we already have a RegExpShared for this pattern/flags, we can
   // avoid the much slower CheckPatternSyntaxSlow call.
 
-  if (RegExpShared* shared = cx->zone()->regExps().maybeGet(pattern, flags)) {
+  RootedRegExpShared shared(cx, cx->zone()->regExps().maybeGet(pattern, flags));
+  if (shared) {
 #ifdef DEBUG
     // Assert the pattern is valid.
     if (!CheckPatternSyntaxSlow(cx, pattern, flags)) {