LibJS: Add Value::to_well_formed_string

Author: https://github.com/shannonbooth
Commit: https://github.com/LadybirdBrowser/ladybird/commit/2e884ff1404
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/998
Reviewed-by: https://github.com/skyrising
Reviewed-by: https://github.com/tcl3 ✅

Userland/Libraries/LibJS/Runtime/StringPrototype.cpp

@@ -1378,6 +1378,13 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::to_well_formed)
     // 2. Let S be ? ToString(O).
     auto string = TRY(utf16_string_from(vm));
 
+    // NOTE: Rest of steps in to_well_formed below
+    return PrimitiveString::create(vm, to_well_formed_string(string));
+}
+
+// https://tc39.es/ecma262/#sec-string.prototype.towellformed
+String to_well_formed_string(Utf16String const& string)
+{
     // 3. Let strLen be the length of S.
     auto length = string.length_in_code_units();
 
@@ -1408,7 +1415,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::to_well_formed)
     }
 
     // 7. Return result.
-    return PrimitiveString::create(vm, MUST(result.to_string()));
+    return MUST(result.to_string());
 }
 
 // 22.1.3.32.1 TrimString ( string, where ), https://tc39.es/ecma262/#sec-trimstring

Userland/Libraries/LibJS/Runtime/StringPrototype.h

@@ -19,6 +19,7 @@ struct CodePoint {
 
 Optional<size_t> string_index_of(Utf16View const& string, Utf16View const& search_value, size_t from_index);
 CodePoint code_point_at(Utf16View const& string, size_t position);
+String to_well_formed_string(Utf16String const&);
 static constexpr Utf8View whitespace_characters = Utf8View("\x09\x0A\x0B\x0C\x0D\x20\xC2\xA0\xE1\x9A\x80\xE2\x80\x80\xE2\x80\x81\xE2\x80\x82\xE2\x80\x83\xE2\x80\x84\xE2\x80\x85\xE2\x80\x86\xE2\x80\x87\xE2\x80\x88\xE2\x80\x89\xE2\x80\x8A\xE2\x80\xAF\xE2\x81\x9F\xE3\x80\x80\xE2\x80\xA8\xE2\x80\xA9\xEF\xBB\xBF"sv);
 ThrowCompletionOr<String> trim_string(VM&, Value string, TrimMode where);
 

Userland/Libraries/LibJS/Runtime/Value.cpp

@@ -453,6 +453,11 @@ ThrowCompletionOr<Utf16String> Value::to_utf16_string(VM& vm) const
     return Utf16String::create(utf8_string.bytes_as_string_view());
 }
 
+ThrowCompletionOr<String> Value::to_well_formed_string(VM& vm) const
+{
+    return ::JS::to_well_formed_string(TRY(to_utf16_string(vm)));
+}
+
 // 7.1.2 ToBoolean ( argument ), https://tc39.es/ecma262/#sec-toboolean
 bool Value::to_boolean_slow_case() const
 {

Userland/Libraries/LibJS/Runtime/Value.h

@@ -384,6 +384,7 @@ public:
     ThrowCompletionOr<String> to_string(VM&) const;
     ThrowCompletionOr<ByteString> to_byte_string(VM&) const;
     ThrowCompletionOr<Utf16String> to_utf16_string(VM&) const;
+    ThrowCompletionOr<String> to_well_formed_string(VM&) const;
     ThrowCompletionOr<NonnullGCPtr<PrimitiveString>> to_primitive_string(VM&);
     ThrowCompletionOr<Value> to_primitive(VM&, PreferredType preferred_type = PreferredType::Default) const;
     ThrowCompletionOr<NonnullGCPtr<Object>> to_object(VM&) const;