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Do not call IsBetterCollectionExpressionConversion for identical collection types. #72706

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merged 1 commit into from
Mar 25, 2024
Merged

Do not call IsBetterCollectionExpressionConversion for identical collection types. #72706

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16 changes: 10 additions & 6 deletions src/Compilers/CSharp/Portable/Binder/Semantics/OverloadResolution/OverloadResolution.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2332,13 +2332,16 @@ private BetterResult BetterFunctionMember<TMember>(
TypeSymbol t1 = m1LeastOverriddenParameters[^1].Type;
TypeSymbol t2 = m2LeastOverriddenParameters[^1].Type;

if (IsBetterParamsCollectionType(t1, t2, ref useSiteInfo))
if (!Conversions.HasIdentityConversion(t1, t2))
{
return BetterResult.Left;
}
if (IsBetterParamsCollectionType(t2, t1, ref useSiteInfo))
{
return BetterResult.Right;
if (IsBetterParamsCollectionType(t1, t2, ref useSiteInfo))
{
return BetterResult.Left;
}
if (IsBetterParamsCollectionType(t2, t1, ref useSiteInfo))
{
return BetterResult.Right;
}
}
}
}
Expand Down Expand Up @@ -2778,6 +2781,7 @@ private bool IsBetterCollectionExpressionConversion(
TypeSymbol t2, CollectionExpressionTypeKind kind2, TypeSymbol elementType2,
ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
Debug.Assert(!Conversions.HasIdentityConversion(t1, t2));

// - T1 is System.ReadOnlySpan<E1>, and T2 is System.Span<E2>, and an implicit conversion exists from E1 to E2
if (kind1 is CollectionExpressionTypeKind.ReadOnlySpan &&
Expand Down
46 changes: 46 additions & 0 deletions src/Compilers/CSharp/Test/Emit2/Semantics/ParamsCollectionTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5723,6 +5723,52 @@ static void Test(int y, params long[] x)
);
}

[Fact]
[WorkItem("https://github.com/dotnet/roslyn/issues/72696")]
public void BetterOverload_04_Ambiguity()
{
var src = """
using System.Collections;
using System.Collections.Generic;

class MyCollection<T> : IEnumerable<T>
{
IEnumerator<T> IEnumerable<T>.GetEnumerator() => throw null;
IEnumerator IEnumerable.GetEnumerator() => throw null;
}

static class ExtensionsA
{
public static void Add<T>(this MyCollection<T> collection, params string[] args) { }
}

static class ExtensionsB
{
public static void Add<T>(this MyCollection<T> collection, params string[] args) { }
}

class Program
{
static void Main()
{
var x = new MyCollection<object>();
x.Add("");

var y = new MyCollection<object> { "" };
}
}
""";
var comp = CreateCompilation(src, targetFramework: TargetFramework.Net80, options: TestOptions.ReleaseExe);
comp.VerifyDiagnostics(
// (25,11): error CS0121: The call is ambiguous between the following methods or properties: 'ExtensionsA.Add<T>(MyCollection<T>, params string[])' and 'ExtensionsB.Add<T>(MyCollection<T>, params string[])'
// x.Add("");
Diagnostic(ErrorCode.ERR_AmbigCall, "Add").WithArguments("ExtensionsA.Add<T>(MyCollection<T>, params string[])", "ExtensionsB.Add<T>(MyCollection<T>, params string[])").WithLocation(25, 11),
// (27,44): error CS0121: The call is ambiguous between the following methods or properties: 'ExtensionsA.Add<T>(MyCollection<T>, params string[])' and 'ExtensionsB.Add<T>(MyCollection<T>, params string[])'
// var y = new MyCollection<object> { "" };
Diagnostic(ErrorCode.ERR_AmbigCall, @"""""").WithArguments("ExtensionsA.Add<T>(MyCollection<T>, params string[])", "ExtensionsB.Add<T>(MyCollection<T>, params string[])").WithLocation(27, 44)
);
}

[Fact]
public void GenericInference()
{
Expand Down
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