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Do not throw when detecting bug Corefx29898 #2123

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Merged
slozier merged 1 commit into from
Oct 29, 2026
Merged

Do not throw when detecting bug Corefx29898 #2123

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37 changes: 30 additions & 7 deletions src/core/IronPython/Runtime/PythonEncoding.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -201,22 +201,45 @@ public override Decoder GetDecoder()
public override byte[] GetPreamble() => Pass1Encoding.GetPreamble();
public override bool IsAlwaysNormalized(NormalizationForm form) => false;

#region BugCorefx29898

public static bool HasBugCorefx29898 {
get {
if (_hasBugCorefx29898 == null) {
try {
var codec = (Encoding)new UTF8Encoding(false, throwOnInvalidBytes: true);
codec.GetCharCount(new byte[] { 255 });
_hasBugCorefx29898 = false;
} catch (DecoderFallbackException ex) {
_hasBugCorefx29898 = (ex.Index < 0);
}
var codec = (Encoding)UTF8.Clone();
codec.DecoderFallback = new TestUtf8DecoderFallback();
var decoder = codec.GetDecoder();
decoder.GetCharCount([255], 0, 1);
_hasBugCorefx29898 = ((TestUtf8DecoderFallbackBuffer)decoder.FallbackBuffer).BugDetected;
}
return (bool)_hasBugCorefx29898;
}
}
private static bool? _hasBugCorefx29898;

private class TestUtf8DecoderFallback : DecoderFallback {
public override int MaxCharCount => 0;

public override DecoderFallbackBuffer CreateFallbackBuffer() => new TestUtf8DecoderFallbackBuffer();
}

private class TestUtf8DecoderFallbackBuffer : DecoderFallbackBuffer {
public bool BugDetected { get; private set; }

public override int Remaining => 0;

public override bool Fallback(byte[] bytesUnknown, int index) {
BugDetected |= (index < 0);
return false;
}

public override char GetNextChar() => '\0';

public override bool MovePrevious() => false;
}

#endregion

internal static int GetUtf16SequenceLength(int rune) => rune > char.MaxValue ? 2 : 1;

private readonly struct MemInt {
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