LibJS: Add spec comments to RegExpConstructor

Userland/Libraries/LibJS/Runtime/RegExpConstructor.cpp

@@ -37,59 +37,91 @@ ThrowCompletionOr<Value> RegExpConstructor::call()
     auto pattern = vm.argument(0);
     auto flags = vm.argument(1);
 
+    // 1. Let patternIsRegExp be ? IsRegExp(pattern).
     bool pattern_is_regexp = TRY(pattern.is_regexp(vm));
 
+    // 2. If NewTarget is undefined, then
+    // a. Let newTarget be the active function object.
+    auto& new_target = *this;
+
+    // b. If patternIsRegExp is true and flags is undefined, then
     if (pattern_is_regexp && flags.is_undefined()) {
+        // i. Let patternConstructor be ? Get(pattern, "constructor").
         auto pattern_constructor = TRY(pattern.as_object().get(vm.names.constructor));
-        if (same_value(this, pattern_constructor))
+
+        // ii. If SameValue(newTarget, patternConstructor) is true, return pattern.
+        if (same_value(&new_target, pattern_constructor))
             return pattern;
     }
 
-    return TRY(construct(*this));
+    return TRY(construct(new_target));
 }
 
 // 22.2.3.1 RegExp ( pattern, flags ), https://tc39.es/ecma262/#sec-regexp-pattern-flags
-ThrowCompletionOr<Object*> RegExpConstructor::construct(FunctionObject&)
+ThrowCompletionOr<Object*> RegExpConstructor::construct(FunctionObject& new_target)
 {
     auto& vm = this->vm();
 
     auto pattern = vm.argument(0);
     auto flags = vm.argument(1);
 
+    // 1. Let patternIsRegExp be ? IsRegExp(pattern).
     bool pattern_is_regexp = TRY(pattern.is_regexp(vm));
 
+    // NOTE: Step 2 is handled in call() above.
+    // 3. Else, let newTarget be NewTarget.
+
     Value pattern_value;
     Value flags_value;
 
+    // 4. If pattern is an Object and pattern has a [[RegExpMatcher]] internal slot, then
     if (pattern.is_object() && is<RegExpObject>(pattern.as_object())) {
+        // a. Let P be pattern.[[OriginalSource]].
         auto& regexp_pattern = static_cast<RegExpObject&>(pattern.as_object());
         pattern_value = js_string(vm, regexp_pattern.pattern());
 
+        // b. If flags is undefined, let F be pattern.[[OriginalFlags]].
         if (flags.is_undefined())
             flags_value = js_string(vm, regexp_pattern.flags());
+        // c. Else, let F be flags.
         else
             flags_value = flags;
-    } else if (pattern_is_regexp) {
+    }
+    // 5. Else if patternIsRegExp is true, then
+    else if (pattern_is_regexp) {
+        // a. Let P be ? Get(pattern, "source").
         pattern_value = TRY(pattern.as_object().get(vm.names.source));
 
+        // b. If flags is undefined, then
         if (flags.is_undefined()) {
+            // i. Let F be ? Get(pattern, "flags").
             flags_value = TRY(pattern.as_object().get(vm.names.flags));
-        } else {
+        }
+        // c. Else, let F be flags.
+        else {
             flags_value = flags;
         }
-    } else {
+    }
+    // 6. Else,
+    else {
+        // a. Let P be pattern.
         pattern_value = pattern;
+
+        // b. Let F be flags.
         flags_value = flags;
     }
 
+    // 7. Let O be ? RegExpAlloc(newTarget).
     auto regexp_object = TRY(regexp_alloc(vm, new_target));
 
+    // 8. Return ? RegExpInitialize(O, P, F).
     return TRY(regexp_object->regexp_initialize(vm, pattern_value, flags_value)).ptr();
 }
 
 // 22.2.4.2 get RegExp [ @@species ], https://tc39.es/ecma262/#sec-get-regexp-@@species
 JS_DEFINE_NATIVE_FUNCTION(RegExpConstructor::symbol_species_getter)
 {
+    // 1. Return the this value.
     return vm.this_value();
 }