Basic Turkish dotted "I" tests with ignore case fail in Turkish culture

[NightOwl888]

Steps to Reproduce

Run the following NUnit tests on Xamarin.Android using Visual Studio 2019 on Windows with the Android emulator.

Note the tests are in a .NET Standard 2.0 library that is referenced by a Xamarin.Android project. I tried a couple of different emulator configurations x86 and x86_64 with similar results. All other tests are running, most passing.

        [Test]
        public void Test_Compare_Turkish_DottedI_IgnoreCase()
        {
            var input = "iiiiiiiiiiiıIiii";
            var test = "İII"; // Turkish capital dotted I test.

            var origCulture = CultureInfo.CurrentCulture;
            try
            {
                CultureInfo.CurrentCulture = new CultureInfo("tr");
                Assert.AreEqual(expected: 0, actual: string.Compare(input, 10, test, 0, 3, StringComparison.CurrentCultureIgnoreCase));
            }
            finally
            {
                CultureInfo.CurrentCulture = origCulture;
            }
        }

        [Test]
        public void Test_Equals_Turkish_DottedI_IgnoreCase()
        {
            var input = "iiiiiiiiiiiıIiii";
            var test = "İII"; // Turkish capital dotted I test.

            var origCulture = CultureInfo.CurrentCulture;
            try
            {
                CultureInfo.CurrentCulture = new CultureInfo("tr");
                Assert.IsTrue(input.Substring(10, 3).Equals(test, StringComparison.CurrentCultureIgnoreCase));
            }
            finally
            {
                CultureInfo.CurrentCulture = origCulture;
            }
        }

Expected Behavior

Case-neutral comparison in Turkish (tr) culture should equate lowercase dotted "I" (ı) with uppercase dotted "I" (İ). These tests pass on .NET Framework 4.8, .NET Core 3.1, and .NET 5.0.

• Comparison for Compare(string, int, string, int, int, StringComparison) should return 0.
• Comparison for string.Equals(string, StringComparison) should return true.

Actual Behavior

• Comparison for Compare(string, int, string, int, int, StringComparison) returns -1.
• Comparison for string.Equals(string, StringComparison) returns false.

Version Information

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Microsoft Visual Studio Community 2019
Version 16.8.2
VisualStudio.16.Release/16.8.2+30717.126
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Version 4.8.04084

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Log File

Log not relevant in this case.

Repro on Azure DevOps

• https://dev.azure.com/NightOwl888/J2N/_build/results?buildId=249&view=ms.vss-test-web.build-test-results-tab&runId=18330&resultId=134521&paneView=debug

See the https://github.com/NightOwl888/J2N repository for configuration details.

[jpobst]

@grendello Are you familiar with which part of the stack handles this? Is it a Mono thing or do we defer to Android for culture information?

[grendello]

@jpobst "traditional" Mono has its own culture tables generated from ICU and it appears to use them on Android as well. I don't know how it works in "dotnet Mono".

[grendello]

@steveisok if you're not the right person to assign this issue too, please reassign :)

[jpobst]

With support for Classic Xamarin.Android ended May 1st, 2024, this issue is likely no longer relevant.

If this still persists in .NET 8+, please open a new issue with updated information based on net8.0-android or greater. Please include a link to this issue for context.