perf: replace array and where clause with ValueStringBuilder

TUnit.Core/Helpers/ValueStringBuilder.cs

@@ -0,0 +1,301 @@
+using System.Buffers;
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace TUnit.Core.Helpers;
+
+// From https://raw.githubusercontent.com/dotnet/runtime/refs/heads/main/src/libraries/Common/src/System/Text/ValueStringBuilder.cs
+internal ref struct ValueStringBuilder
+{
+    private char[]? _arrayToReturnToPool;
+    private Span<char> _chars;
+    private int _pos;
+
+    public ValueStringBuilder(Span<char> initialBuffer)
+    {
+        _arrayToReturnToPool = null;
+        _chars = initialBuffer;
+        _pos = 0;
+    }
+
+    public ValueStringBuilder(int initialCapacity)
+    {
+        _arrayToReturnToPool = ArrayPool<char>.Shared.Rent(initialCapacity);
+        _chars = _arrayToReturnToPool;
+        _pos = 0;
+    }
+
+    public int Length
+    {
+        get => _pos;
+        set
+        {
+            Debug.Assert(value >= 0);
+            Debug.Assert(value <= _chars.Length);
+            _pos = value;
+        }
+    }
+
+    public int Capacity => _chars.Length;
+
+    public void EnsureCapacity(int capacity)
+    {
+        // This is not expected to be called this with negative capacity
+        Debug.Assert(capacity >= 0);
+
+        // If the caller has a bug and calls this with negative capacity, make sure to call Grow to throw an exception.
+        if ((uint)capacity > (uint)_chars.Length)
+            Grow(capacity - _pos);
+    }
+
+    /// <summary>
+    /// Ensures that the builder is terminated with a NUL character.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void NullTerminate()
+    {
+        EnsureCapacity(_pos + 1);
+        _chars[_pos] = '\0';
+    }
+
+    /// <summary>
+    /// Get a pinnable reference to the builder.
+    /// Does not ensure there is a null char after <see cref="Length"/>
+    /// This overload is pattern matched in the C# 7.3+ compiler so you can omit
+    /// the explicit method call, and write eg "fixed (char* c = builder)"
+    /// </summary>
+    public ref char GetPinnableReference()
+    {
+        return ref MemoryMarshal.GetReference(_chars);
+    }
+
+    public ref char this[int index]
+    {
+        get
+        {
+            Debug.Assert(index < _pos);
+            return ref _chars[index];
+        }
+    }
+
+    public override string ToString()
+    {
+        string s = _chars.Slice(0, _pos).ToString();
+        Dispose();
+        return s;
+    }
+
+    /// <summary>Returns the underlying storage of the builder.</summary>
+    public Span<char> RawChars => _chars;
+
+    public ReadOnlySpan<char> AsSpan() => _chars.Slice(0, _pos);
+    public ReadOnlySpan<char> AsSpan(int start) => _chars.Slice(start, _pos - start);
+    public ReadOnlySpan<char> AsSpan(int start, int length) => _chars.Slice(start, length);
+
+    public void Insert(int index, char value, int count)
+    {
+        if (_pos > _chars.Length - count)
+        {
+            Grow(count);
+        }
+
+        int remaining = _pos - index;
+        _chars.Slice(index, remaining).CopyTo(_chars.Slice(index + count));
+        _chars.Slice(index, count).Fill(value);
+        _pos += count;
+    }
+
+    public void Insert(int index, string? s)
+    {
+        if (s == null)
+        {
+            return;
+        }
+
+        int count = s.Length;
+
+        if (_pos > (_chars.Length - count))
+        {
+            Grow(count);
+        }
+
+        int remaining = _pos - index;
+        _chars.Slice(index, remaining).CopyTo(_chars.Slice(index + count));
+        s
+#if !NET
+            .AsSpan()
+#endif
+            .CopyTo(_chars.Slice(index));
+        _pos += count;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void Append(char c)
+    {
+        int pos = _pos;
+        Span<char> chars = _chars;
+        if ((uint)pos < (uint)chars.Length)
+        {
+            chars[pos] = c;
+            _pos = pos + 1;
+        }
+        else
+        {
+            GrowAndAppend(c);
+        }
+    }
+
+    public void Append(int value) => AppendSpanFormattable(value);
+
+    #if NET8_0_OR_GREATER
+    private void AppendSpanFormattable<T>(T value) 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");
+
+        if (value.TryFormat(_chars, out int charsWritten, format: default, provider: null))
+        {
+            _pos += charsWritten;
+            return;
+        }
+
+        Append(value.ToString());
+    }
+#else
+    private void AppendSpanFormattable<T>(T value)
+    {
+        Append(value!.ToString());
+    }
+#endif
+
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void Append(string? s)
+    {
+        if (s == null)
+        {
+            return;
+        }
+
+        int pos = _pos;
+        if (s.Length == 1 && (uint)pos < (uint)_chars.Length) // very common case, e.g. appending strings from NumberFormatInfo like separators, percent symbols, etc.
+        {
+            _chars[pos] = s[0];
+            _pos = pos + 1;
+        }
+        else
+        {
+            AppendSlow(s);
+        }
+    }
+
+    private void AppendSlow(string s)
+    {
+        int pos = _pos;
+        if (pos > _chars.Length - s.Length)
+        {
+            Grow(s.Length);
+        }
+
+        s
+#if !NET
+            .AsSpan()
+#endif
+            .CopyTo(_chars.Slice(pos));
+        _pos += s.Length;
+    }
+
+    public void Append(char c, int count)
+    {
+        if (_pos > _chars.Length - count)
+        {
+            Grow(count);
+        }
+
+        Span<char> dst = _chars.Slice(_pos, count);
+        for (int i = 0; i < dst.Length; i++)
+        {
+            dst[i] = c;
+        }
+        _pos += count;
+    }
+
+    public void Append(scoped ReadOnlySpan<char> value)
+    {
+        int pos = _pos;
+        if (pos > _chars.Length - value.Length)
+        {
+            Grow(value.Length);
+        }
+
+        value.CopyTo(_chars.Slice(_pos));
+        _pos += value.Length;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public Span<char> AppendSpan(int length)
+    {
+        int origPos = _pos;
+        if (origPos > _chars.Length - length)
+        {
+            Grow(length);
+        }
+
+        _pos = origPos + length;
+        return _chars.Slice(origPos, length);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private void GrowAndAppend(char c)
+    {
+        Grow(1);
+        Append(c);
+    }
+
+    /// <summary>
+    /// Resize the internal buffer either by doubling current buffer size or
+    /// by adding <paramref name="additionalCapacityBeyondPos"/> to
+    /// <see cref="_pos"/> whichever is greater.
+    /// </summary>
+    /// <param name="additionalCapacityBeyondPos">
+    /// Number of chars requested beyond current position.
+    /// </param>
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private void Grow(int additionalCapacityBeyondPos)
+    {
+        Debug.Assert(additionalCapacityBeyondPos > 0);
+        Debug.Assert(_pos > _chars.Length - additionalCapacityBeyondPos, "Grow called incorrectly, no resize is needed.");
+
+        const uint ArrayMaxLength = 0x7FFFFFC7; // same as Array.MaxLength
+
+        // Increase to at least the required size (_pos + additionalCapacityBeyondPos), but try
+        // to double the size if possible, bounding the doubling to not go beyond the max array length.
+        int newCapacity = (int)Math.Max(
+            (uint)(_pos + additionalCapacityBeyondPos),
+            Math.Min((uint)_chars.Length * 2, ArrayMaxLength));
+
+        // Make sure to let Rent throw an exception if the caller has a bug and the desired capacity is negative.
+        // This could also go negative if the actual required length wraps around.
+        char[] poolArray = ArrayPool<char>.Shared.Rent(newCapacity);
+
+        _chars.Slice(0, _pos).CopyTo(poolArray);
+
+        char[]? toReturn = _arrayToReturnToPool;
+        _chars = _arrayToReturnToPool = poolArray;
+        if (toReturn != null)
+        {
+            ArrayPool<char>.Shared.Return(toReturn);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void Dispose()
+    {
+        char[]? toReturn = _arrayToReturnToPool;
+        this = default; // for safety, to avoid using pooled array if this instance is erroneously appended to again
+        if (toReturn != null)
+        {
+            ArrayPool<char>.Shared.Return(toReturn);
+        }
+    }
+}

TUnit.Core/TestContext.Output.cs

@@ -1,4 +1,5 @@
 using System.Collections.Concurrent;
+using TUnit.Core.Helpers;
 using TUnit.Core.Interfaces;
 
 namespace TUnit.Core;
@@ -75,29 +76,45 @@ public override string GetErrorOutput()
 
     internal string GetOutput()
     {
+        var vsb = new ValueStringBuilder(stackalloc char[256]);
+
         var buildOutput = _buildTimeOutput ?? string.Empty;
         var baseOutput = base.GetStandardOutput();  // Get output from base class (Context)
         var writerOutput = _outputWriter?.ToString() ?? string.Empty;
 
-        // Combine all three sources: build-time, base class output, and writer output
-        var parts = new[] { buildOutput, baseOutput, writerOutput }
-            .Where(s => !string.IsNullOrEmpty(s))
-            .ToArray();
+        AppendIfNotNullOrEmpty(ref vsb, buildOutput);
+        AppendIfNotNullOrEmpty(ref vsb, baseOutput);
+        AppendIfNotNullOrEmpty(ref vsb, writerOutput);
 
-        return parts.Length == 0 ? string.Empty : string.Join(Environment.NewLine, parts);
+        return vsb.ToString();
     }
 
     internal string GetOutputError()
     {
+        var vsb = new ValueStringBuilder(stackalloc char[256]);
+
         var buildErrorOutput = _buildTimeErrorOutput ?? string.Empty;
         var baseErrorOutput = base.GetErrorOutput();  // Get error output from base class (Context)
         var writerErrorOutput = _errorWriter?.ToString() ?? string.Empty;
 
-        // Combine all three sources: build-time error, base class error output, and writer error output
-        var parts = new[] { buildErrorOutput, baseErrorOutput, writerErrorOutput }
-            .Where(s => !string.IsNullOrEmpty(s))
-            .ToArray();
+        AppendIfNotNullOrEmpty(ref vsb, buildErrorOutput);
+        AppendIfNotNullOrEmpty(ref vsb, baseErrorOutput);
+        AppendIfNotNullOrEmpty(ref vsb, writerErrorOutput);
+
+        return vsb.ToString();
+    }
+
+    private static void AppendIfNotNullOrEmpty(ref ValueStringBuilder builder, string? value)
+    {
+        if (string.IsNullOrEmpty(value))
+        {
+            return;
+        }
 
-        return parts.Length == 0 ? string.Empty : string.Join(Environment.NewLine, parts);
+        if (builder.Length > 0)
+        {
+            builder.Append(Environment.NewLine);
+        }
+        builder.Append(value);
     }
 }