Disallow 'var' as an explicit lambda expression return type #56911
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AlekseyTs
reviewed
Oct 1, 2021
| var resetPoint = this.GetResetPoint(); | ||
| try | ||
| { | ||
| returnType = ParseReturnType(); | ||
| if (CurrentToken.Kind != SyntaxKind.OpenParenToken) | ||
| if (!IsVarType()) |
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Done with review pass (commit 2) |
AlekseyTs
reviewed
Oct 1, 2021
| @@ -12787,6 +12787,12 @@ LambdaExpressionSyntax parseLambdaExpressionWorker() | |||
| arrow = CheckFeatureAvailability(arrow, MessageID.IDS_FeatureLambda); | |||
| var (block, expression) = ParseLambdaBody(); | |||
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| // Disallow 'var' as explicit return type. | |||
| if ((returnType as IdentifierNameSyntax)?.Identifier.ContextualKind == SyntaxKind.VarKeyword) | |||
AlekseyTs
reviewed
Oct 1, 2021
| void verify(string source, ParseOptions? parseOptions = null) | ||
| { | ||
| UsingDeclaration(source, parseOptions, | ||
| // (1,9): error CS1031: Type expected |
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Perhaps error CS0825: The contextual keyword 'var' may only appear within a local variable declaration or in script code is suitable. SharpLab
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Moved PR to target |
AlekseyTs
reviewed
Oct 1, 2021
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| // Breaking change from C#9 which binds calls to F(Func<Func<object>>, int). | ||
| // | ||
| // The calls such as F(() => () => 1, 2) should be considered ambiguous in C#9 as per the C# spec. |
jcouv
reviewed
Oct 1, 2021
| @@ -248,6 +248,11 @@ static void checkAttributes(AnonymousFunctionExpressionSyntax syntax, SyntaxList | |||
| MessageID.IDS_FeatureLambdaReturnType.CheckFeatureAvailability(diagnostics, syntax); | |||
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| syntax = syntax.SkipRef(out RefKind refKind); | |||
| if ((syntax as IdentifierNameSyntax)?.Identifier.ContextualKind() == SyntaxKind.VarKeyword) | |||
| { | |||
| diagnostics.Add(ErrorCode.ERR_LambdaExplicitReturnTypeVar, syntax.Location); | |||
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Probably should document as breaking change in 17.1 #Pending
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Does the spec capture that design decision?
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I've added an item to the breaking changes document. I'll update the spec in a subsequent PR.
jcouv
approved these changes
Oct 1, 2021
AlekseyTs
reviewed
Oct 1, 2021
| { | ||
| static void Main() | ||
| { | ||
| F(var (var v) => v); |
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Perhaps there is a mismatch in source for VerifyDiagnostics below.
ghost
modified the milestones:
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See LDM-2021-06-02 notes.
Relates to #52192