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Merged
AlekseyTs merged 1 commit into from
Feb 13, 2026
Merged

Unions: Address/remove some PROTOTYPE comments #82381

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3 changes: 0 additions & 3 deletions src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/ConversionsBase.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -471,8 +471,6 @@ private Conversion ClassifyConversionFromTypeForCast(TypeSymbol source, TypeSymb
//
// fail.

// PROTOTYPE: Note, an explicit user-defined conversion may come before a union conversion in this case.
// Confirm that this is acceptable.
var conversion = GetExplicitUserDefinedConversion(source, destination, isChecked: isChecked, ref useSiteInfo);
if (conversion.Exists)
{
Expand Down Expand Up @@ -791,7 +789,6 @@ private Conversion GetImplicitUserDefinedOrUnionConversion(BoundExpression sourc
return result;
}

// PROTOTYPE: Confirm that union conversions are considered after user-defined conversions.
Conversion unionConversion = AnalyzeImplicitUnionConversions(sourceExpression, source, destination, ref useSiteInfo);

if (unionConversion.Exists)
Expand Down
2 changes: 0 additions & 2 deletions src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/UserDefinedImplicitConversions.cs
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Expand Up @@ -991,8 +991,6 @@ private Conversion AnalyzeImplicitUnionConversions(
Debug.Assert(sourceExpression != null || (object)source != null);
Debug.Assert((object)target != null);

// PROTOTYPE: It might make sense to block conversions from a base class or any interface. See comments in tests.

if (target.StrippedType() is not NamedTypeSymbol namedTarget || !namedTarget.IsUnionTypeWithUseSiteDiagnostics(ref useSiteInfo))
{
return Conversion.NoConversion;
Expand Down
8 changes: 5 additions & 3 deletions src/Compilers/CSharp/Portable/Binder/SwitchBinder.cs
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Expand Up @@ -268,10 +268,12 @@ protected BoundExpression ConvertCaseExpression(CSharpSyntaxNode node, BoundExpr
hasErrors = true;
}

caseExpression = CreateConversion(caseExpression, conversion, SwitchGoverningType, diagnostics);
if (!conversion.IsUnion)
{
caseExpression = CreateConversion(caseExpression, conversion, SwitchGoverningType, diagnostics);
}
}

// PROTOTYPE: Test that consumer actually does the right thing when a union matching is involved. Cover error scenarios as well.
var inputType = SwitchGoverningType;
NamedTypeSymbol unionType = PrepareForUnionMatchingIfAppropriateAndReturnUnionType(node, ref inputType, diagnostics);
return ConvertPatternExpression(unionType, inputType, node, caseExpression, out constantValueOpt, hasErrors, diagnostics, out _);
Expand Down Expand Up @@ -433,7 +435,7 @@ private BoundExpression BindSwitchGoverningExpression(BindingDiagnosticBag diagn
if (conversion.IsValid)
{
// Condition (2) satisfied
Debug.Assert(conversion.Kind == ConversionKind.ImplicitUserDefined); // PROTOTYPE: Follow up
Debug.Assert(conversion.Kind == ConversionKind.ImplicitUserDefined);
Debug.Assert(conversion.Method.IsUserDefinedConversion());
Debug.Assert(conversion.UserDefinedToConversion.IsIdentity);
Debug.Assert(resultantGoverningType.IsValidV6SwitchGoverningType(isTargetTypeOfUserDefinedOp: true));
Expand Down
2 changes: 0 additions & 2 deletions src/Compilers/CSharp/Portable/Symbols/NamedTypeSymbol.cs
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Expand Up @@ -1843,8 +1843,6 @@ internal ImmutableArray<TypeSymbol> UnionCaseTypes
internal static bool IsSuitableUnionConstructor(MethodSymbol ctor)
{
Debug.Assert(ctor.MethodKind is MethodKind.Constructor);
// PROTOTYPE: Confirm RefKind restriction. Conversion operators allow only RefKind.None or RefKind.In.
// It feels like it makes sense to use the same restriction here.
return ctor is { DeclaredAccessibility: Accessibility.Public, ParameterCount: 1, Parameters: [{ RefKind: RefKind.In or RefKind.None }] };
}

Expand Down
178 changes: 156 additions & 22 deletions src/Compilers/CSharp/Test/CSharp15/UnionsTests.cs
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Expand Up @@ -2360,6 +2360,160 @@ .maxstack 2
");
}

[Fact]
public void UnionMatching_36_SwitchStatement()
{
var src = @"
struct S1 : System.Runtime.CompilerServices.IUnion
{
private readonly object _value;
public S1(int x) { _value = x; }
public S1(string x) { _value = x; }
object System.Runtime.CompilerServices.IUnion.Value => _value;
}

class Program
{
static void Main()
{
System.Console.Write(Test1(new S1(10)));
System.Console.Write(Test1(new S1(""10"")));
System.Console.Write(Test1(default));
System.Console.Write(Test1(new S1(11)));
System.Console.Write(Test1(new S1(""11"")));
System.Console.Write(Test1(new S1(0)));
}

static int Test1(S1 u)
{
switch (u)
{
case 10: return 1;
case ""11"": return 2;
}

return -1;
}
}
";
var comp = CreateCompilation([src, IUnionSource], options: TestOptions.ReleaseExe);
CompileAndVerify(comp, expectedOutput: "1-1-1-12-1").VerifyDiagnostics();
}

[Fact]
public void UnionMatching_37_SwitchStatement()
{
var src = @"
struct S1 : System.Runtime.CompilerServices.IUnion
{
private readonly object _value;
public S1(int x) { _value = x; }
public S1(string x) { _value = x; }
object System.Runtime.CompilerServices.IUnion.Value => _value;
}

class Program
{
static void Main()
{
System.Console.Write(Test1(new S1(10)));
System.Console.Write(Test1(new S1(""10"")));
System.Console.Write(Test1(default));
System.Console.Write(Test1(new S1(11)));
System.Console.Write(Test1(new S1(""11"")));
System.Console.Write(Test1(new S1(0)));
}

static int Test1(S1 u)
{
switch (u)
{
case 10: goto case 44;
case ""11"": goto case ""55"";
case 44: return 44;
case ""55"": return 55;
}

return -1;
}
}
";
var comp = CreateCompilation([src, IUnionSource], options: TestOptions.ReleaseExe);
CompileAndVerify(comp, expectedOutput: "44-1-1-155-1").VerifyDiagnostics();
}

[Fact]
public void UnionMatching_38_SwitchStatement()
{
var src = @"
struct S1 : System.Runtime.CompilerServices.IUnion
{
private readonly object _value;
public S1(int x) { _value = x; }
public S1(string x) { _value = x; }
object System.Runtime.CompilerServices.IUnion.Value => _value;
}

class Program
{
static int Test1(S1 u)
{
switch (u)
{
case 10: return 1;
case ""11"": return 2;
case true: return 3;
}

return -1;
}
}
";
var comp = CreateCompilation([src, IUnionSource]);
comp.VerifyDiagnostics(
// (18,18): error CS8121: An expression of type 'S1' cannot be handled by a pattern of type 'bool'.
// case true: return 3;
Diagnostic(ErrorCode.ERR_PatternWrongType, "true").WithArguments("S1", "bool").WithLocation(18, 18)
);
}

[Fact]
public void UnionMatching_39_SwitchStatement()
{
var src = @"
struct S1 : System.Runtime.CompilerServices.IUnion
{
private readonly object _value;
public S1(int x) { _value = x; }
public S1(string x) { _value = x; }
object System.Runtime.CompilerServices.IUnion.Value => _value;
}

class Program
{
static int Test1(S1 u)
{
switch (u)
{
case 10: goto case true;
case ""11"": return 2;
}

return -1;
}
}
";
var comp = CreateCompilation([src, IUnionSource]);
comp.VerifyDiagnostics(
// (16,13): error CS0163: Control cannot fall through from one case label ('case 10:') to another
// case 10: goto case true;
Diagnostic(ErrorCode.ERR_SwitchFallThrough, "case 10:").WithArguments("case 10:").WithLocation(16, 13),
// (16,22): error CS0029: Cannot implicitly convert type 'bool' to 'S1'
// case 10: goto case true;
Diagnostic(ErrorCode.ERR_NoImplicitConv, "goto case true;").WithArguments("bool", "S1").WithLocation(16, 22)
);
}

[Fact]
public void PatternWrongType_TypePattern_01_BindConstantPatternWithFallbackToTypePattern_UnionType_Out_UnionType_In()
{
Expand Down Expand Up @@ -3148,7 +3302,8 @@ static void Test1(S1 u)
// case 1:
Diagnostic(ErrorCode.ERR_SwitchFallOut, "case 1:").WithArguments("case 1:").WithLocation(102, 13),

// PROTOTYPE: This doesn't look like a union matching error. Something is likely missing in implementation.
// The following error is expected per language specification (https://github.com/dotnet/csharpstandard/blob/draft-v8/standard/statements.md#13104-the-goto-statement):
// "if the constant_expression is not implicitly convertible (§10.2) to the governing type of the nearest enclosing switch statement, a compile-time error occurs."

// (103,17): error CS0029: Cannot implicitly convert type 'string' to 'S1'
// goto case empty;
Expand Down Expand Up @@ -5222,8 +5377,6 @@ static S1 Test1(int? x)
";
var comp = CreateCompilation([src, IUnionSource]);

// PROTOTYPE: Confirm that there are no lifted forms.

comp.VerifyDiagnostics(
// (20,16): error CS0029: Cannot implicitly convert type 'int?' to 'S1'
// return x;
Expand Down Expand Up @@ -5781,11 +5934,6 @@ static S1 Test2(System.ValueType x)
var comp = CreateCompilation([src, IUnionSource], options: TestOptions.ReleaseExe);
var verifier = CompileAndVerify(comp, expectedOutput: "System.ValueType S1").VerifyDiagnostics();

// PROTOTYPE: Confirm that we are fine with this conversion behavior. See previous test as well.
// Cast performs unboxing conversion, but implicit conversion performs union conversion.
// Might be too confusing.
// Note, language disallows user-defined conversions like that, see errors below.

verifier.VerifyIL("Program.Test2", @"
{
// Code size 7 (0x7)
Expand Down Expand Up @@ -5889,11 +6037,6 @@ static S1 Test2(I1 x)
var comp = CreateCompilation([src, IUnionSource], options: TestOptions.ReleaseExe);
var verifier = CompileAndVerify(comp, expectedOutput: "I1 S1").VerifyDiagnostics();

// PROTOTYPE: Confirm that we are fine with this conversion behavior. See previous test as well.
// Cast performs unboxing conversion, but implicit conversion performs union conversion.
// Might be too confusing.
// Note, language disallows user-defined conversions like that, see errors below.

verifier.VerifyIL("Program.Test2", @"
{
// Code size 7 (0x7)
Expand Down Expand Up @@ -5968,10 +6111,6 @@ static S1 Test2(I1 x)
var comp = CreateCompilation([src, IUnionSource], options: TestOptions.ReleaseExe);
var verifier = CompileAndVerify(comp, expectedOutput: "I1 S1 I1 S1").VerifyDiagnostics();

// PROTOTYPE: Confirm that we are fine with this conversion behavior.
// Might be too confusing.
// Note, language disallows user-defined conversions like that, see errors below.

verifier.VerifyIL("Program.Test1", @"
{
// Code size 7 (0x7)
Expand Down Expand Up @@ -6054,11 +6193,6 @@ static S1 Test2(I1 x)
var comp = CreateCompilation([src, IUnionSource], options: TestOptions.ReleaseExe);
var verifier = CompileAndVerify(comp, expectedOutput: "I1 S1").VerifyDiagnostics();

// PROTOTYPE: Confirm that we are fine with this conversion behavior.
// Cast performs castclass conversion, but implicit conversion performs union conversion.
// Might be too confusing.
// Note, language disallows user-defined conversions like that, see errors below.

verifier.VerifyIL("Program.Test1", @"
{
// Code size 7 (0x7)
Expand Down
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