From 3f75cf270ad827c0c685e5e4f6fe4ed9ecf45228 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Sun, 20 Jul 2025 12:52:53 -0400
Subject: [PATCH] LibJS: Move ambiguous Temporal time string handling to a
 separate parser

This is an editorial change in the Temporal proposal. See:
https://github.com/tc39/proposal-temporal/commit/fa3d0b9
---
 Libraries/LibJS/Runtime/Temporal/ISO8601.cpp  | 21 ++++++++++---------
 Libraries/LibJS/Runtime/Temporal/ISO8601.h    |  3 ++-
 .../LibJS/Runtime/Temporal/PlainTime.cpp      | 13 ++++++------
 .../Temporal/PlainTime/PlainTime.from.js      |  2 +-
 4 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/Libraries/LibJS/Runtime/Temporal/ISO8601.cpp b/Libraries/LibJS/Runtime/Temporal/ISO8601.cpp
index 946f4f7acc9..6606efa0c14 100644
--- a/Libraries/LibJS/Runtime/Temporal/ISO8601.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/ISO8601.cpp
@@ -150,6 +150,15 @@ public:
         return parse_annotated_date_time(Zoned::No, TimeRequired::Yes) || parse_annotated_time();
     }
 
+    // https://tc39.es/proposal-temporal/#prod-AmbiguousTemporalTimeString
+    [[nodiscard]] bool parse_ambiguous_temporal_time_string()
+    {
+        // AmbiguousTemporalTimeString :::
+        //     DateSpecMonthDay TimeZoneAnnotation[opt] Annotations[opt]
+        //     DateSpecYearMonth TimeZoneAnnotation[opt] Annotations[opt]
+        return parse_annotated_month_day() || parse_annotated_year_month();
+    }
+
     // https://tc39.es/proposal-temporal/#prod-TemporalYearMonthString
     [[nodiscard]] bool parse_temporal_year_month_string()
     {
@@ -199,16 +208,7 @@ public:
         // AnnotatedTime :::
         //     TimeDesignator Time DateTimeUTCOffset[~Z][opt] TimeZoneAnnotation[opt] Annotations[opt]
         //     Time DateTimeUTCOffset[~Z][opt] TimeZoneAnnotation[opt] Annotations[opt]
-        auto has_time_designator = parse_time_designator();
-
-        if (!has_time_designator) {
-            StateTransaction transaction { *this };
-
-            // It is a Syntax Error if ParseText(Time DateTimeUTCOffset[~Z], DateSpecMonthDay) is a Parse Node.
-            // It is a Syntax Error if ParseText(Time DateTimeUTCOffset[~Z], DateSpecYearMonth) is a Parse Node.
-            if (parse_date_spec_month_day() || parse_date_spec_year_month())
-                return false;
-        }
+        (void)parse_time_designator();
 
         if (!parse_time())
             return false;
@@ -1303,6 +1303,7 @@ private:
 };
 
 #define JS_ENUMERATE_ISO8601_PRODUCTION_PARSERS                                        \
+    __JS_ENUMERATE(AmbiguousTemporalTimeString, parse_ambiguous_temporal_time_string)  \
     __JS_ENUMERATE(AnnotationValue, parse_annotation_value)                            \
     __JS_ENUMERATE(DateMonth, parse_date_month)                                        \
     __JS_ENUMERATE(TemporalDateTimeString, parse_temporal_date_time_string)            \
diff --git a/Libraries/LibJS/Runtime/Temporal/ISO8601.h b/Libraries/LibJS/Runtime/Temporal/ISO8601.h
index 298732868e9..6e350e91433 100644
--- a/Libraries/LibJS/Runtime/Temporal/ISO8601.h
+++ b/Libraries/LibJS/Runtime/Temporal/ISO8601.h
@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2021-2022, Linus Groh <linusg@serenityos.org>
- * Copyright (c) 2024, Tim Flynn <trflynn89@ladybird.org>
+ * Copyright (c) 2024-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -60,6 +60,7 @@ struct ParseResult {
 };
 
 enum class Production {
+    AmbiguousTemporalTimeString,
     AnnotationValue,
     DateMonth,
     TemporalDateTimeString,
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainTime.cpp b/Libraries/LibJS/Runtime/Temporal/PlainTime.cpp
index ea6c35e3ab9..1430c15de65 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainTime.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainTime.cpp
@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
  * Copyright (c) 2021-2023, Linus Groh <linusg@serenityos.org>
- * Copyright (c) 2024, Tim Flynn <trflynn89@ladybird.org>
+ * Copyright (c) 2024-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -169,15 +169,16 @@ ThrowCompletionOr<GC::Ref<PlainTime>> to_temporal_time(VM& vm, Value item, Value
         // b. Let parseResult be ? ParseISODateTime(item, « TemporalTimeString »).
         auto parse_result = TRY(parse_iso_date_time(vm, item.as_string().utf8_string_view(), { { Production::TemporalTimeString } }));
 
-        // c. Assert: parseResult.[[Time]] is not START-OF-DAY.
+        // c. If ParseText(StringToCodePoints(item), AmbiguousTemporalTimeString) is a Parse Node, throw a RangeError exception.
+        if (parse_iso8601(Production::AmbiguousTemporalTimeString, item.as_string().utf8_string_view()).has_value())
+            return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidPlainTime);
+
+        // d. Assert: parseResult.[[Time]] is not START-OF-DAY.
         VERIFY(!parse_result.time.has<ParsedISODateTime::StartOfDay>());
 
-        // d. Set result to parseResult.[[Time]].
+        // e. Set result to parseResult.[[Time]].
         time = parse_result.time.get<Time>();
 
-        // e. NOTE: A successful parse using TemporalTimeString guarantees absence of ambiguity with respect to any
-        //    ISO 8601 date-only, year-month, or month-day representation.
-
         // f. Let resolvedOptions be ? GetOptionsObject(options).
         auto resolved_options = TRY(get_options_object(vm, options));
 
diff --git a/Libraries/LibJS/Tests/builtins/Temporal/PlainTime/PlainTime.from.js b/Libraries/LibJS/Tests/builtins/Temporal/PlainTime/PlainTime.from.js
index 1c2b5b97a80..40ccd5f2296 100644
--- a/Libraries/LibJS/Tests/builtins/Temporal/PlainTime/PlainTime.from.js
+++ b/Libraries/LibJS/Tests/builtins/Temporal/PlainTime/PlainTime.from.js
@@ -68,7 +68,7 @@ describe("errors", () => {
         for (const value of values) {
             expect(() => {
                 Temporal.PlainTime.from(value);
-            }).toThrowWithMessage(RangeError, "Invalid ISO date time");
+            }).toThrowWithMessage(RangeError, "Invalid plain time");
 
             expect(() => {
                 Temporal.PlainTime.from(`T${value}`);