[inspector] Support printing RegExps with overridden `toString`

Prior to this patch, regular expression objects with a monkeypatched
`toString` were printed using the `toString` result value, rather than
actually representing the regular expression’s contents.

    const re = /./;
    re.toString = () => 'whoops!';
    console.log(re);
    // → logs 'whoops!'

Now that `v8::RegExp::GetSource` properly escapes special characters in
the source pattern [1], just like `RegExp#toString`, there is no longer
any reason to avoid it.

[1]: https://chromium-review.googlesource.com/c/v8/v8/+/2900737

Bug: v8:11693
Change-Id: I9a69cdb6813f76b669bdc24e4823c6d261f2ae73
Fixed: v8:11836
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2928188Reviewed-by: Philip Pfaffe <pfaffe@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74862}

src/inspector/value-mirror.cc

@@ -220,19 +220,22 @@ String16 descriptionForPrimitiveType(v8::Local<v8::Context> context,
   return String16();
 }
 
-String16 descriptionForObject(v8::Isolate* isolate,
-                              v8::Local<v8::Object> object) {
-  return toProtocolString(isolate, object->GetConstructorName());
-}
-
-String16 descriptionForRegExp(v8::Local<v8::Context> context,
+String16 descriptionForRegExp(v8::Isolate* isolate,
                               v8::Local<v8::RegExp> value) {
-  v8::Isolate* isolate = context->GetIsolate();
-  v8::Local<v8::String> description;
-  if (!value->ToString(context).ToLocal(&description)) {
-    return descriptionForObject(isolate, value);
-  }
-  return toProtocolString(isolate, description);
+  String16Builder description;
+  description.append('/');
+  description.append(toProtocolString(isolate, value->GetSource()));
+  description.append('/');
+  v8::RegExp::Flags flags = value->GetFlags();
+  if (flags & v8::RegExp::Flags::kHasIndices) description.append('d');
+  if (flags & v8::RegExp::Flags::kGlobal) description.append('g');
+  if (flags & v8::RegExp::Flags::kIgnoreCase) description.append('i');
+  if (flags & v8::RegExp::Flags::kLinear) description.append('l');
+  if (flags & v8::RegExp::Flags::kMultiline) description.append('m');
+  if (flags & v8::RegExp::Flags::kDotAll) description.append('s');
+  if (flags & v8::RegExp::Flags::kUnicode) description.append('u');
+  if (flags & v8::RegExp::Flags::kSticky) description.append('y');
+  return description.toString();
 }
 
 enum class ErrorType { kNative, kClient };
@@ -290,6 +293,11 @@ String16 descriptionForError(v8::Local<v8::Context> context,
   return description + stackWithoutMessage;
 }
 
+String16 descriptionForObject(v8::Isolate* isolate,
+                              v8::Local<v8::Object> object) {
+  return toProtocolString(isolate, object->GetConstructorName());
+}
+
 String16 descriptionForDate(v8::Local<v8::Context> context,
                             v8::Local<v8::Date> date) {
   v8::Isolate* isolate = context->GetIsolate();
@@ -1617,7 +1625,7 @@ std::unique_ptr<ValueMirror> ValueMirror::create(v8::Local<v8::Context> context,
   if (value->IsRegExp()) {
     return std::make_unique<ObjectMirror>(
         value, RemoteObject::SubtypeEnum::Regexp,
-        descriptionForRegExp(context, value.As<v8::RegExp>()));
+        descriptionForRegExp(isolate, value.As<v8::RegExp>()));
   }
   if (value->IsProxy()) {
     return std::make_unique<ObjectMirror>(

test/inspector/runtime/remote-object-expected.txt

@@ -497,6 +497,18 @@ Running test: testRegExp
         type : object
     }
 }
+'var re = /./dgimsuy;
+        re.toString = () => 'foo';
+        re', returnByValue: false, generatePreview: false
+{
+    result : {
+        className : RegExp
+        description : /./dgimsuy
+        objectId : <objectId>
+        subtype : regexp
+        type : object
+    }
+}
 'var re = new RegExp('\w+', 'g');
         re.prop = 32;
         re', returnByValue: false, generatePreview: true

test/inspector/runtime/remote-object.js

@@ -230,6 +230,11 @@ InspectorTest.runAsyncTestSuite([
     InspectorTest.logMessage((await evaluate({
       expression: `new RegExp('foo/bar')`
     })).result);
+    InspectorTest.logMessage((await evaluate({
+      expression: `var re = /./dgimsuy;
+        re.toString = () => 'foo';
+        re`
+    })).result);
     InspectorTest.logMessage((await evaluate({
       expression: `var re = new RegExp('\\w+', 'g');
         re.prop = 32;