Compiled & source-generated Regex throw IndexOutOfRangeException on a nested optional containing a lazy capturing loop

[janipulkkinen]

Description

A pattern combining an outer optional group wrapping an inner optional capturing group followed by a lazily-quantified capturing loop and a trailing literal throws System.IndexOutOfRangeException during matching under both RegexOptions.Compiled and the [GeneratedRegex] source generator. The interpreter matches the same input correctly (empty successful match).

Note: similar to #126556, but a different defect — it still reproduces on 11.0.0-preview.5.26302.115, which already contains the #126556 fix (PR #126561).

Reproduction Steps

using System.Text.RegularExpressions;

partial class Program
{
    private const string Pattern = @"((a+(:c*)?@)?([0-9]|A){1,4}?:)?";

    [GeneratedRegex(Pattern)]
    private static partial Regex Generated();

    static void Main()
    {
        const string input = "1234";
        Console.WriteLine(new Regex(Pattern).Match(input).Success); // OK: empty match
        new Regex(Pattern, RegexOptions.Compiled).Match(input);            // throws IndexOutOfRangeException
        Generated().Match(input);                                          // throws IndexOutOfRangeException
    }
}

Expected behavior

All three engines should agree (interpreter returns a successful empty match). Instead Compiled and [GeneratedRegex] throw IndexOutOfRangeException in TryMatchAtCurrentPosition.

Actual behavior

Compiled and [GeneratedRegex] throw IndexOutOfRangeException in TryMatchAtCurrentPosition.

Regression?

No response

Known Workarounds

No response

Configuration

.NET 8.0.26 / 9.0.15 / 10.0.7 / 11.0.0-preview.5.26302.115
Windows 11 x64

Other information

No response

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