Improve MSTest.SourceGeneration incrementality

src/Analyzers/MSTest.SourceGeneration/Helpers/EquatableArray{T}.cs

@@ -0,0 +1,190 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under dual-license. See LICENSE.PLATFORMTOOLS.txt file in the project root for full license information.
+
+using System.Collections.Immutable;
+
+namespace MSTest.SourceGeneration.Helpers;
+
+// Copy from https://github.com/Sergio0694/ComputeSharp/blob/120aff270539996ef9fc52fe46561d12da0b89d4/src/ComputeSharp.SourceGeneration/Helpers/EquatableArray%7BT%7D.cs
+
+/// <summary>
+/// Extensions for <see cref="EquatableArray{T}"/>.
+/// </summary>
+internal static class EquatableArray
+{
+    /// <summary>
+    /// Creates an <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of items in the input array.</typeparam>
+    /// <param name="array">The input <see cref="ImmutableArray{T}"/> instance.</param>
+    /// <returns>An <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.</returns>
+    public static EquatableArray<T> AsEquatableArray<T>(this ImmutableArray<T> array)
+        where T : IEquatable<T>
+        => new(array);
+}
+
+/// <summary>
+/// An imutable, equatable array. This is equivalent to <see cref="ImmutableArray{T}"/> but with value equality support.
+/// </summary>
+/// <typeparam name="T">The type of values in the array.</typeparam>
+/// <param name="array">The input <see cref="ImmutableArray{T}"/> to wrap.</param>
+internal readonly struct EquatableArray<T>(ImmutableArray<T> array) : IEquatable<EquatableArray<T>>, IEnumerable<T>
+    where T : IEquatable<T>
+{
+    /// <summary>
+    /// The underlying <typeparamref name="T"/> array.
+    /// </summary>
+    private readonly T[]? _array = Unsafe.As<ImmutableArray<T>, T[]?>(ref array);
+
+    /// <summary>
+    /// Gets a reference to an item at a specified position within the array.
+    /// </summary>
+    /// <param name="index">The index of the item to retrieve a reference to.</param>
+    /// <returns>A reference to an item at a specified position within the array.</returns>
+    public ref readonly T this[int index]
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => ref AsImmutableArray().ItemRef(index);
+    }
+
+    /// <summary>
+    /// Gets a value indicating whether the current array is empty.
+    /// </summary>
+    public bool IsEmpty
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => AsImmutableArray().IsEmpty;
+    }
+
+    /// <summary>
+    /// Gets a value indicating whether the current array is default or empty.
+    /// </summary>
+    public bool IsDefaultOrEmpty
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => AsImmutableArray().IsDefaultOrEmpty;
+    }
+
+    /// <summary>
+    /// Gets the length of the current array.
+    /// </summary>
+    public int Length
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => AsImmutableArray().Length;
+    }
+
+    /// <inheritdoc/>
+    public bool Equals(EquatableArray<T> array)
+        => AsSpan().SequenceEqual(array.AsSpan());
+
+    public override bool Equals(object? obj)
+        => obj is EquatableArray<T> array && Equals(this, array);
+
+    /// <inheritdoc/>
+    public override unsafe int GetHashCode()
+    {
+        if (_array is not T[] array)
+        {
+            return 0;
+        }
+
+        HashCode hashCode = default;
+
+        if (typeof(T) == typeof(byte))
+        {
+            ReadOnlySpan<T> span = array;
+            ref T r0 = ref MemoryMarshal.GetReference(span);
+            ref byte r1 = ref Unsafe.As<T, byte>(ref r0);
+
+            fixed (byte* p = &r1)
+            {
+                ReadOnlySpan<byte> bytes = new(p, span.Length);
+
+                hashCode.AddBytes(bytes);
+            }
+        }
+        else
+        {
+            foreach (T item in array)
+            {
+                hashCode.Add(item);
+            }
+        }
+
+        return hashCode.ToHashCode();
+    }
+
+    /// <summary>
+    /// Gets an <see cref="ImmutableArray{T}"/> instance from the current <see cref="EquatableArray{T}"/>.
+    /// </summary>
+    /// <returns>The <see cref="ImmutableArray{T}"/> from the current <see cref="EquatableArray{T}"/>.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public ImmutableArray<T> AsImmutableArray()
+        => Unsafe.As<T[]?, ImmutableArray<T>>(ref Unsafe.AsRef(in _array));
+
+    /// <summary>
+    /// Creates an <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.
+    /// </summary>
+    /// <param name="array">The input <see cref="ImmutableArray{T}"/> instance.</param>
+    /// <returns>An <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.</returns>
+    public static EquatableArray<T> FromImmutableArray(ImmutableArray<T> array)
+        => new(array);
+
+    /// <summary>
+    /// Returns a <see cref="ReadOnlySpan{T}"/> wrapping the current items.
+    /// </summary>
+    /// <returns>A <see cref="ReadOnlySpan{T}"/> wrapping the current items.</returns>
+    public ReadOnlySpan<T> AsSpan()
+        => AsImmutableArray().AsSpan();
+
+    /// <summary>
+    /// Copies the contents of this <see cref="EquatableArray{T}"/> instance. to a mutable array.
+    /// </summary>
+    /// <returns>The newly instantiated array.</returns>
+    public T[] ToArray()
+        => [.. AsImmutableArray()];
+
+    /// <summary>
+    /// Gets an <see cref="ImmutableArray{T}.Enumerator"/> value to traverse items in the current array.
+    /// </summary>
+    /// <returns>An <see cref="ImmutableArray{T}.Enumerator"/> value to traverse items in the current array.</returns>
+    public ImmutableArray<T>.Enumerator GetEnumerator()
+        => AsImmutableArray().GetEnumerator();
+
+    /// <inheritdoc/>
+    IEnumerator<T> IEnumerable<T>.GetEnumerator()
+        => ((IEnumerable<T>)AsImmutableArray()).GetEnumerator();
+
+    /// <inheritdoc/>
+    IEnumerator IEnumerable.GetEnumerator()
+        => ((IEnumerable)AsImmutableArray()).GetEnumerator();
+
+    /// <summary>
+    /// Implicitly converts an <see cref="ImmutableArray{T}"/> to <see cref="EquatableArray{T}"/>.
+    /// </summary>
+    /// <returns>An <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.</returns>
+    public static implicit operator EquatableArray<T>(ImmutableArray<T> array) => FromImmutableArray(array);
+
+    /// <summary>
+    /// Implicitly converts an <see cref="EquatableArray{T}"/> to <see cref="ImmutableArray{T}"/>.
+    /// </summary>
+    /// <returns>An <see cref="ImmutableArray{T}"/> instance from a given <see cref="EquatableArray{T}"/>.</returns>
+    public static implicit operator ImmutableArray<T>(EquatableArray<T> array) => array.AsImmutableArray();
+
+    /// <summary>
+    /// Checks whether two <see cref="EquatableArray{T}"/> values are the same.
+    /// </summary>
+    /// <param name="left">The first <see cref="EquatableArray{T}"/> value.</param>
+    /// <param name="right">The second <see cref="EquatableArray{T}"/> value.</param>
+    /// <returns>Whether <paramref name="left"/> and <paramref name="right"/> are equal.</returns>
+    public static bool operator ==(EquatableArray<T> left, EquatableArray<T> right) => left.Equals(right);
+
+    /// <summary>
+    /// Checks whether two <see cref="EquatableArray{T}"/> values are not the same.
+    /// </summary>
+    /// <param name="left">The first <see cref="EquatableArray{T}"/> value.</param>
+    /// <param name="right">The second <see cref="EquatableArray{T}"/> value.</param>
+    /// <returns>Whether <paramref name="left"/> and <paramref name="right"/> are not equal.</returns>
+    public static bool operator !=(EquatableArray<T> left, EquatableArray<T> right) => !left.Equals(right);
+}