From ee7ab5d053bb0cc5d90b460a252ad7df65fb6d14 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Tue, 7 Nov 2023 09:52:37 -0500
Subject: [PATCH] LibCore: Support wildcard-skipping characters in
 Core::DateTime::parse

For example, LibJS will need to parse date strings of the form:

    Wed Dec 31 1969 19:00:00 GMT-0500 (Eastern Standard Time)

This string contains both the time zone offset (-05:00) and a display
name for the time zone (Eastern Standard Time). Because we will already
handle time zone adjustments when we handle the offsets, we will want to
just skip the time zone name. This patch will let us use a format string
of the form "GMT%z (%+)" to do so.
---
 Tests/LibCore/TestLibCoreDateTime.cpp   | 23 +++++++++++++++++++++++
 Userland/Libraries/LibCore/DateTime.cpp | 18 ++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/Tests/LibCore/TestLibCoreDateTime.cpp b/Tests/LibCore/TestLibCoreDateTime.cpp
index 0fde0d3065..d412ce6b1d 100644
--- a/Tests/LibCore/TestLibCoreDateTime.cpp
+++ b/Tests/LibCore/TestLibCoreDateTime.cpp
@@ -83,3 +83,26 @@ TEST_CASE(parse_time_zone_name)
     test("%Y/%m/%d %R %Z"sv, "2023/01/23 10:50 Europe/Paris"sv, 2023, 01, 23, 17, 50);
     test("%Y/%m/%d %R %Z"sv, "2023/01/23 10:50 Australia/Perth"sv, 2023, 01, 23, 10, 50);
 }
+
+TEST_CASE(parse_wildcard_characters)
+{
+    EXPECT(!Core::DateTime::parse("%+"sv, ""sv).has_value());
+    EXPECT(!Core::DateTime::parse("foo%+"sv, "foo"sv).has_value());
+    EXPECT(!Core::DateTime::parse("[%*]"sv, "[foo"sv).has_value());
+    EXPECT(!Core::DateTime::parse("[%*]"sv, "foo]"sv).has_value());
+    EXPECT(!Core::DateTime::parse("%+%b"sv, "fooJan"sv).has_value());
+
+    auto test = [](auto format, auto time, u32 year, u32 month, u32 day) {
+        auto result = Core::DateTime::parse(format, time);
+        VERIFY(result.has_value());
+
+        EXPECT_EQ(year, result->year());
+        EXPECT_EQ(month, result->month());
+        EXPECT_EQ(day, result->day());
+    };
+
+    test("%Y %+ %m %d"sv, "2023 whf 01 23"sv, 2023, 01, 23);
+    test("%Y %m %d %+"sv, "2023 01 23 whf"sv, 2023, 01, 23);
+    test("%Y [%+] %m %d"sv, "2023 [well hello friends!] 01 23"sv, 2023, 01, 23);
+    test("%Y %m %d [%+]"sv, "2023 01 23 [well hello friends!]"sv, 2023, 01, 23);
+}
diff --git a/Userland/Libraries/LibCore/DateTime.cpp b/Userland/Libraries/LibCore/DateTime.cpp
index 11ecba36e2..000d684e0d 100644
--- a/Userland/Libraries/LibCore/DateTime.cpp
+++ b/Userland/Libraries/LibCore/DateTime.cpp
@@ -512,6 +512,24 @@ Optional<DateTime> DateTime::parse(StringView format, StringView string)
 
             tm_represents_utc_time = true;
             break;
+        case '+': {
+            Optional<char> next_format_character;
+
+            if (format_pos + 1 < format.length()) {
+                next_format_character = format[format_pos + 1];
+
+                // Disallow another formatter directly after %+. This is to avoid ambiguity when parsing a string like
+                // "ignoreJan" with "%+%b", as it would be non-trivial to know that where the %b field begins.
+                if (next_format_character == '%')
+                    return {};
+            }
+
+            auto discarded = string_lexer.consume_until([&](auto ch) { return ch == next_format_character; });
+            if (discarded.is_empty())
+                return {};
+
+            break;
+        }
         case '%':
             consume('%');
             break;