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Lambda expression explicit return type: binding #54075

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Jun 21, 2021
Merged

Lambda expression explicit return type: binding #54075

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Lambda expression explicit return type: binding
cston Jun 8, 2021
9b2d9ed
Update NullableWalker
cston Jun 14, 2021
f8f6c7a
Fix warning
cston Jun 15, 2021
08d21a9
PR feedback
cston Jun 15, 2021
a752010
Add tests
cston Jun 15, 2021
6c05d62
Fix tests
cston Jun 19, 2021
ed9af13
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cston Jun 19, 2021
20a262b
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cston Jun 16, 2021
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8 changes: 8 additions & 0 deletions src/Compilers/CSharp/Portable/Binder/Binder.QueryUnboundLambdaState.cs
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Expand Up @@ -35,6 +35,14 @@ public QueryUnboundLambdaState(Binder binder, RangeVariableMap rangeVariableMap,
public override SyntaxList<AttributeListSyntax> ParameterAttributes(int index) => default;
public override bool HasNames { get { return true; } }
public override bool HasSignature { get { return true; } }

public override bool HasExplicitReturnType(out RefKind refKind, out TypeWithAnnotations returnType)
{
refKind = default;
returnType = default;
return false;
}

public override bool HasExplicitlyTypedParameterList { get { return false; } }
public override int ParameterCount { get { return _parameters.Length; } }
public override bool IsAsync { get { return false; } }
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38 changes: 32 additions & 6 deletions src/Compilers/CSharp/Portable/Binder/Binder_Lambda.cs
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Expand Up @@ -38,10 +38,12 @@ private UnboundLambda AnalyzeAnonymousFunction(
Debug.Assert(syntax != null);
Debug.Assert(syntax.IsAnonymousFunction());

var names = default(ImmutableArray<string>);
var refKinds = default(ImmutableArray<RefKind>);
var types = default(ImmutableArray<TypeWithAnnotations>);
var attributes = default(ImmutableArray<SyntaxList<AttributeListSyntax>>);
ImmutableArray<string> names = default;
ImmutableArray<RefKind> refKinds = default;
ImmutableArray<TypeWithAnnotations> types = default;
RefKind returnRefKind = RefKind.None;
TypeWithAnnotations returnType = default;
ImmutableArray<SyntaxList<AttributeListSyntax>> parameterAttributes = default;

var namesBuilder = ArrayBuilder<string>.GetInstance();
ImmutableArray<bool> discardsOpt = default;
Expand All @@ -67,6 +69,10 @@ private UnboundLambda AnalyzeAnonymousFunction(
// (x, y) => ...
hasSignature = true;
var paren = (ParenthesizedLambdaExpressionSyntax)syntax;
if (paren.ReturnType is { } returnTypeSyntax)
{
(returnRefKind, returnType) = BindExplicitLambdaReturnType(returnTypeSyntax, diagnostics);
}
parameterSyntaxList = paren.ParameterList.Parameters;
CheckParenthesizedLambdaParameters(parameterSyntaxList.Value, diagnostics);
break;
Expand Down Expand Up @@ -187,7 +193,7 @@ private UnboundLambda AnalyzeAnonymousFunction(

if (attributesBuilder.Any(a => a.Count > 0))
{
attributes = attributesBuilder.ToImmutable();
parameterAttributes = attributesBuilder.ToImmutable();
}

typesBuilder.Free();
Expand All @@ -202,7 +208,7 @@ private UnboundLambda AnalyzeAnonymousFunction(

namesBuilder.Free();

return new UnboundLambda(syntax, this, diagnostics.AccumulatesDependencies, attributes, refKinds, types, names, discardsOpt, isAsync, isStatic);
return new UnboundLambda(syntax, this, diagnostics.AccumulatesDependencies, returnRefKind, returnType, parameterAttributes, refKinds, types, names, discardsOpt, isAsync, isStatic);

static ImmutableArray<bool> computeDiscards(SeparatedSyntaxList<ParameterSyntax> parameters, int underscoresCount)
{
Expand Down Expand Up @@ -237,6 +243,26 @@ static void checkAttributes(AnonymousFunctionExpressionSyntax syntax, SyntaxList
}
}

private (RefKind, TypeWithAnnotations) BindExplicitLambdaReturnType(TypeSyntax syntax, BindingDiagnosticBag diagnostics)
{
MessageID.IDS_FeatureLambdaReturnType.CheckFeatureAvailability(diagnostics, syntax);

syntax = syntax.SkipRef(out RefKind refKind);
var returnType = BindType(syntax, diagnostics);
var type = returnType.Type;

if (returnType.IsStatic)
{
diagnostics.Add(ErrorFacts.GetStaticClassReturnCode(useWarning: false), syntax.Location, type);
}
else if (returnType.IsRestrictedType(ignoreSpanLikeTypes: true))
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@333fred 333fred Jun 17, 2021 •
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Theoretically, when we start inferring delegate types, we could encounter an async function with an __arglist parameter. Do we need to check that here? Or perhaps assert that we'll never encounter such a scenario? SourceOrdinaryMethodSymbolBase checks this case in its equivalent method, so I think we should do something about it, even if it's just to assert we'll never hit it. #Closed

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Is this an issue introduced by explicit return types or an existing issue with lambda parameters?

It looks like the parser rejects __arglist in IsPossibleLambdaParameter(). I've added some parsing tests.

{
diagnostics.Add(ErrorCode.ERR_MethodReturnCantBeRefAny, syntax.Location, type);
}

return (refKind, returnType);
}

private static void CheckParenthesizedLambdaParameters(
SeparatedSyntaxList<ParameterSyntax> parameterSyntaxList, BindingDiagnosticBag diagnostics)
{
Expand Down
13 changes: 11 additions & 2 deletions src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs
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Expand Up @@ -1809,6 +1809,7 @@ internal BoundExpression GenerateConversionForAssignment(TypeSymbol targetType,
return CreateConversion(expression.Syntax, expression, conversion, isCast: false, conversionGroupOpt: null, targetType, diagnostics);
}

#nullable enable
internal void GenerateAnonymousFunctionConversionError(BindingDiagnosticBag diagnostics, SyntaxNode syntax,
UnboundLambda anonymousFunction, TypeSymbol targetType)
{
Expand Down Expand Up @@ -1868,9 +1869,13 @@ internal void GenerateAnonymousFunctionConversionError(BindingDiagnosticBag diag
return;
}

// At this point we know that we have either a delegate type or an expression type for the target.
if (reason == LambdaConversionResult.MismatchedReturnType)
{
Error(diagnostics, ErrorCode.ERR_CantConvAnonMethReturnType, syntax, id, targetType);
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@jcouv jcouv Jun 15, 2021 •
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nit: The name of the error code suggests that conversions have something to do, but the logic and message are that the types have to match. Consider renaming the error code and diagnostic. #Closed

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Never mind. I see that we're using same naming convention for parameter types (ERR_CantConvAnonMethParams). Fine as-is then

return;
}

var delegateType = targetType.GetDelegateType();
// At this point we know that we have either a delegate type or an expression type for the target.

// The target type is a valid delegate or expression tree type. Is there something wrong with the
// parameter list?
Expand All @@ -1896,6 +1901,9 @@ internal void GenerateAnonymousFunctionConversionError(BindingDiagnosticBag diag
return;
}

var delegateType = targetType.GetDelegateType();
Debug.Assert(delegateType is not null);

// There is a parameter list. Does it have the right number of elements?

if (reason == LambdaConversionResult.BadParameterCount)
Expand Down Expand Up @@ -2013,6 +2021,7 @@ internal void GenerateAnonymousFunctionConversionError(BindingDiagnosticBag diag
Debug.Assert(false, "Missing case in lambda conversion error reporting");
diagnostics.Add(ErrorCode.ERR_InternalError, syntax.Location);
}
#nullable disable

protected static void GenerateImplicitConversionError(BindingDiagnosticBag diagnostics, CSharpCompilation compilation, SyntaxNode syntax,
Conversion conversion, TypeSymbol sourceType, TypeSymbol targetType, ConstantValue sourceConstantValueOpt = null)
Expand Down
11 changes: 10 additions & 1 deletion src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/ConversionsBase.cs
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Expand Up @@ -1246,7 +1246,6 @@ source.Type is object &&
IsNumericType(source.Type) &&
IsConstantNumericZero(sourceConstantValue);
}
#nullable disable

private static LambdaConversionResult IsAnonymousFunctionCompatibleWithDelegate(UnboundLambda anonymousFunction, TypeSymbol type)
{
Expand All @@ -1266,6 +1265,15 @@ private static LambdaConversionResult IsAnonymousFunctionCompatibleWithDelegate(
return LambdaConversionResult.BadTargetType;
}

if (anonymousFunction.HasExplicitReturnType(out var refKind, out var returnType))
{
if (invokeMethod.RefKind != refKind ||
!invokeMethod.ReturnType.Equals(returnType.Type, TypeCompareKind.AllIgnoreOptions))
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@jcouv jcouv Jun 15, 2021 •
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Are we sure this is the rule we want? Does this fall out of existing spec rules, or needs to be spec'ed?

On one hand, Func<int> f = localFunctionReturningShort; an error (with short localFunctionReturningShort()). So Func<int> f = short () => 1; makes sense to error as well.
On the other hand, I think Func<object, int> f = (o) => 1; involves a conversion from expression which gives o its object type, so why wouldn't that conversion also handle Func<object, int> f = short (o) => 1? #Closed

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@jcouv jcouv Jun 15, 2021 •
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Also, is AllIgnoreOptions the right option? Can we include tests for types differing by small differences (object vs. dynamic, nullability, custom modifiers)?

Update: I see LambdaReturnType_04 covers most of those. Is there a way to get into a situation with a custom modifiers difference as well?

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@cston cston Jun 15, 2021 •
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Are we sure this is the rule we want? Does this fall out of existing spec rules, or needs to be spec'ed?

This should be confirmed with LDM, but I believe it corresponds to the behavior for parameters. For instance, Action<string> a = (object o) => { }; results in a conversion error (see sharplab.io).

Can we include tests for types differing by small differences (object vs. dynamic, nullability, custom modifiers)?

There are tests for object and dynamic, tuple element names, nint and IntPtr, and nullable differences.

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You're correct, this is the behavior for parameters: https://github.com/dotnet/csharplang/blob/main/spec/conversions.md#anonymous-function-conversions
"If F has an explicitly typed parameter list, each parameter in D has the same type and modifiers as the corresponding parameter in F."

We probably need to add a similar rule to the spec for the return type.

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These things should just fall out. Variance only allows for implicit reference conversions, nothing else, because they need to be representation-preserving.

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Is there a way to get into a situation with a custom modifiers difference as well?

Added tests for custom modifiers.

{
return LambdaConversionResult.MismatchedReturnType;
}
}

var delegateParameters = invokeMethod.Parameters;

// SPEC: If F contains an anonymous-function-signature, then D and F have the same number of parameters.
Expand Down Expand Up @@ -1426,6 +1434,7 @@ private static bool HasAnonymousFunctionConversion(BoundExpression source, TypeS

return IsAnonymousFunctionCompatibleWithType((UnboundLambda)source, destination) == LambdaConversionResult.Success;
}
#nullable disable

internal Conversion ClassifyImplicitUserDefinedConversionForV6SwitchGoverningType(TypeSymbol sourceType, out TypeSymbol switchGoverningType, ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
{
Expand Down
7 changes: 1 addition & 6 deletions src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/LambdaConversionResult.cs
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Expand Up @@ -2,12 +2,6 @@
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#nullable disable

using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp
{
internal enum LambdaConversionResult
Expand All @@ -16,6 +10,7 @@ internal enum LambdaConversionResult
BadTargetType,
BadParameterCount,
MissingSignatureWithOutParameter,
MismatchedReturnType,
MismatchedParameterType,
RefInImplicitlyTypedLambda,
StaticTypeInImplicitlyTypedLambda,
Expand Down
26 changes: 9 additions & 17 deletions src/Compilers/CSharp/Portable/Binder/WithLambdaParametersBinder.cs
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Expand Up @@ -5,7 +5,6 @@
#nullable disable

using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Diagnostics;
using Microsoft.CodeAnalysis.CSharp.Symbols;
Expand All @@ -18,7 +17,7 @@ internal class WithLambdaParametersBinder : LocalScopeBinder
{
protected readonly LambdaSymbol lambdaSymbol;
protected readonly MultiDictionary<string, ParameterSymbol> parameterMap;
private SmallDictionary<string, ParameterSymbol> _definitionMap;
private readonly SmallDictionary<string, ParameterSymbol> _definitionMap;

public WithLambdaParametersBinder(LambdaSymbol lambdaSymbol, Binder enclosing)
: base(enclosing)
Expand All @@ -29,24 +28,17 @@ public WithLambdaParametersBinder(LambdaSymbol lambdaSymbol, Binder enclosing)
var parameters = lambdaSymbol.Parameters;
if (!parameters.IsDefaultOrEmpty)
{
recordDefinitions(parameters);
foreach (var parameter in lambdaSymbol.Parameters)
_definitionMap = new SmallDictionary<string, ParameterSymbol>();
foreach (var parameter in parameters)
{
if (!parameter.IsDiscard)
{
this.parameterMap.Add(parameter.Name, parameter);
}
}
}

void recordDefinitions(ImmutableArray<ParameterSymbol> definitions)
{
var declarationMap = _definitionMap ??= new SmallDictionary<string, ParameterSymbol>();
foreach (var s in definitions)
{
if (!s.IsDiscard && !declarationMap.ContainsKey(s.Name))
{
declarationMap.Add(s.Name, s);
var name = parameter.Name;
this.parameterMap.Add(name, parameter);
if (!_definitionMap.ContainsKey(name))
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@jcouv jcouv Jun 15, 2021 •
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We don't need the IsDiscard check after all (either on parameterMap or on _definitionMap)? #Closed

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Oops, missed it above ;-)

{
_definitionMap.Add(name, parameter);
}
}
}
}
Expand Down
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