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Add support for ISpanFormattable in StringBuilder.Append(Object)
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@manandre
manandre committed Feb 19, 2024
1 parent 07992e2 commit 917f9e5
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Showing 2 changed files with 91 additions and 9 deletions.
22 changes: 18 additions & 4 deletions src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1052,12 +1052,19 @@ private void AppendWithExpansion(char value)
[CLSCompliant(false)]
public StringBuilder Append(ulong value) => AppendSpanFormattable(value);

private StringBuilder AppendSpanFormattable<T>(T value) where T : ISpanFormattable
private StringBuilder AppendSpanFormattable<T>(T value, bool untrusted = false) where T : ISpanFormattable
{
Debug.Assert(typeof(T).Assembly.Equals(typeof(object).Assembly), "Implementation trusts the results of TryFormat because T is expected to be something known");
Debug.Assert(untrusted || typeof(T).Assembly.Equals(typeof(object).Assembly), "Implementation trusts the results of TryFormat because T is expected to be something known");

if (value.TryFormat(RemainingCurrentChunk, out int charsWritten, format: default, provider: null))
{
if (untrusted && ((uint)charsWritten > (uint)RemainingCurrentChunkLength))
{
// Protect against faulty ISpanFormattable implementations returning invalid charsWritten values.
// Other code in _stringBuilder uses Unsafe manipulation, and we want to ensure m_ChunkLength remains safe.
ThrowHelper.ThrowFormatInvalidString();
}

m_ChunkLength += charsWritten;
return this;
}
Expand All @@ -1078,7 +1085,12 @@ internal StringBuilder AppendSpanFormattable<T>(T value, string? format, IFormat
return Append(value.ToString(format, provider));
}

public StringBuilder Append(object? value) => (value == null) ? this : Append(value.ToString());
public StringBuilder Append(object? value) => value switch
{
null => this,
ISpanFormattable sf => AppendSpanFormattable(sf, untrusted: true),
object o => Append(o.ToString())
};

public StringBuilder Append(char[]? value)
{
Expand Down Expand Up @@ -1620,7 +1632,7 @@ internal StringBuilder AppendFormatHelper(IFormatProvider? provider, string form
arg is ISpanFormattable spanFormattableArg &&
spanFormattableArg.TryFormat(RemainingCurrentChunk, out int charsWritten, itemFormatSpan, provider))
{
if ((uint)charsWritten > (uint)RemainingCurrentChunk.Length)
if ((uint)charsWritten > (uint)RemainingCurrentChunkLength)
{
// Untrusted ISpanFormattable implementations might return an erroneous charsWritten value,
// and m_ChunkLength might end up being used in Unsafe code, so fail if we get back an
Expand Down Expand Up @@ -2423,6 +2435,8 @@ private Span<char> RemainingCurrentChunk
get => new Span<char>(m_ChunkChars, m_ChunkLength, m_ChunkChars.Length - m_ChunkLength);
}

private int RemainingCurrentChunkLength => m_ChunkChars.Length - m_ChunkLength;

/// <summary>
/// Finds the chunk that logically succeeds the specified chunk.
/// </summary>
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78 changes: 73 additions & 5 deletions src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Text/StringBuilderTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -378,18 +378,86 @@ public static void Append_Long_NoSpareCapacity_ThrowsArgumentOutOfRangeException
AssertExtensions.Throws<ArgumentOutOfRangeException>(s_noCapacityParamName, () => builder.Append((long)1));
}

public static IEnumerable<object[]> Append_Object_TestData()
{
yield return new object[] { "Hello", "abc", "Helloabc" };
yield return new object[] { "", "g", "g" };
yield return new object[] { "Hello", "", "Hello" };
yield return new object[] { "Hello", null, "Hello" };
yield return new object[] { "Hello", $"abc", "Helloabc" };
// ISpanFormattable inputs: simple validation of known types that implement the interface
yield return new object[] { "", (byte)42, "42" };
yield return new object[] { "", 'A', "A" };
yield return new object[] { "", DateTime.ParseExact("2021-03-15T14:52:51.5058563Z", "o", null, DateTimeStyles.AdjustToUniversal | DateTimeStyles.AssumeUniversal), "3/15/2021 2:52:51 PM" };
yield return new object[] { "", DateTimeOffset.ParseExact("2021-03-15T14:52:51.5058563Z", "o", null, DateTimeStyles.AdjustToUniversal | DateTimeStyles.AssumeUniversal), "3/15/2021 2:52:51 PM +00:00" };
yield return new object[] { "", (decimal)42, "42" };
yield return new object[] { "", (double)42, "42" };
yield return new object[] { "", Guid.Parse("68d9cfaf-feab-4d5b-96d8-a3fd889ae89f"), "68d9cfaf-feab-4d5b-96d8-a3fd889ae89f" };
yield return new object[] { "", (Half)42, "42" };
yield return new object[] { "", (short)42, "42" };
yield return new object[] { "", (int)42, "42" };
yield return new object[] { "", (long)42, "42" };
yield return new object[] { "", (IntPtr)42, "42" };
yield return new object[] { "", new Rune('A'), "A" };
yield return new object[] { "", (sbyte)42, "42" };
yield return new object[] { "", (float)42, "42" };
yield return new object[] { "", TimeSpan.FromSeconds(42), "00:00:42" };
yield return new object[] { "", (ushort)42, "42" };
yield return new object[] { "", (uint)42, "42" };
yield return new object[] { "", (ulong)42, "42" };
yield return new object[] { "", (UIntPtr)42, "42" };
yield return new object[] { "", new Version(1, 2, 3, 4), "1.2.3.4" };
// ISpanFormattable inputs: advanced validation to ensure that ToString() is not called by default.
yield return new object[] { "Hello", new FormattableStringWithSpanOnly("abc"), "Helloabc" };
yield return new object[] { "Hello", $"{new FormattableStringWithSpanOnly("abc")}", "Helloabc" };
}

private struct FormattableStringWithSpanOnly : ISpanFormattable
{
private string _value;

public FormattableStringWithSpanOnly(string value) => _value = value;

public override readonly string ToString() => throw new NotImplementedException();
public readonly string ToString(string? format, IFormatProvider? formatProvider) => ToString();

public bool TryFormat(Span<char> destination, out int charsWritten, ReadOnlySpan<char> format, IFormatProvider? provider) =>
destination.TryWrite($"{_value}", out charsWritten);
}

[Theory]
[InlineData("Hello", "abc", "Helloabc")]
[InlineData("Hello", "def", "Hellodef")]
[InlineData("", "g", "g")]
[InlineData("Hello", "", "Hello")]
[InlineData("Hello", null, "Hello")]
[MemberData(nameof(Append_Object_TestData))]
public static void Append_Object(string original, object value, string expected)
{
var builder = new StringBuilder(original);
builder.Append(value);
Assert.Equal(expected, builder.ToString());
}

[Theory]
[InlineData(false)]
[InlineData(true)]
public void Append_Object_InvalidTryFormatCharsWritten_Throws(bool tooBig) // vs tooSmall
{
var builder = new StringBuilder();
Assert.Throws<FormatException>(() => builder.Append(new InvalidCharsWritten(tooBig)));
}

private sealed class InvalidCharsWritten : ISpanFormattable
{
private bool _tooBig;

public InvalidCharsWritten(bool tooBig) => _tooBig = tooBig;

public bool TryFormat(Span<char> destination, out int charsWritten, ReadOnlySpan<char> format, IFormatProvider provider)
{
charsWritten = _tooBig ? destination.Length + 1 : -1;
return true;
}

public string ToString(string format, IFormatProvider formatProvider) =>
throw new NotImplementedException();
}

[Fact]
public static void Append_Object_NoSpareCapacity_ThrowsArgumentOutOfRangeException()
Expand Down

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