Bug 1606084 - Add RegExp support to ValueToSource fallback. r=arai

Differential Revision: https://phabricator.services.mozilla.com/D59685

--HG--
extra : moz-landing-system : lando

js/src/jit-test/tests/basic/valuetosource.js

@@ -20,6 +20,8 @@ const TEST_CASES = [
             this.name = "X";
         }
     }, `(new X("msg", "file", 1))`],
+    [/a(b)c/, `/a(b)c/`],
+    [/abc/gi, `/abc/gi`],
 ]
 
 for (let [actual, expected] of TEST_CASES) {

js/src/vm/CommonPropertyNames.h

@@ -366,6 +366,7 @@
   MACRO(RegExpSearcher, RegExpSearcher, "RegExpSearcher")                      \
   MACRO(RegExpStringIterator, RegExpStringIterator, "RegExp String Iterator")  \
   MACRO(RegExpTester, RegExpTester, "RegExpTester")                            \
+  MACRO(RegExpToString, RegExpToString, "$RegExpToString")                     \
   MACRO(RegExp_prototype_Exec, RegExp_prototype_Exec, "RegExp_prototype_Exec") \
   MACRO(region, region, "region")                                              \
   MACRO(register, register_, "register")                                       \

js/src/vm/ToSource.cpp

@@ -28,6 +28,9 @@
 #include "vm/JSContext.h"       // JSContext
 #include "vm/JSFunction.h"      // JSFunction, FunctionToString
 #include "vm/Printer.h"         // QuoteString
+#include "vm/RegExpObject.h"    // RegExpObject
+#include "vm/SelfHosting.h"     // CallSelfHostedFunction
+#include "vm/Stack.h"           // FixedInvokeArgs
 #include "vm/StringType.h"      // NewStringCopy{N,Z}, ToString
 #include "vm/SymbolType.h"      // Symbol
 
@@ -132,5 +135,15 @@ JSString* js::ValueToSource(JSContext* cx, HandleValue v) {
     return ErrorToSource(cx, obj);
   }
 
+  if (obj->is<RegExpObject>()) {
+    FixedInvokeArgs<0> args(cx);
+    RootedValue rval(cx);
+    if (!CallSelfHostedFunction(cx, cx->names().RegExpToString, v, args,
+                                &rval)) {
+      return nullptr;
+    }
+    return ToString<CanGC>(cx, rval);
+  }
+
   return ObjectToSource(cx, obj);
 }