[API proposal]: GetDeclaredSymbol for lambdas

[Youssef1313]

Background and Motivation

The node kinds SyntaxKind.AnonymousMethodExpression, SyntaxKind.ParenthesizedLambdaExpression, and SyntaxKind.SimpleLambdaExpression declares lambda symbols, but not supported by GetDeclaredSymbol

Proposed API

namespace Microsoft.CodeAnalysis.CSharp
{
     internal class CSharpSemanticModel
     {
+        public abstract ISymbol GetDeclaredSymbol(AnonymousFunctionExpressionSyntax anonymousFunctionSyntax, CancellationToken cancellationToken = default(CancellationToken));
     }

namespace Microsoft.CodeAnalysis
{
     public static class CSharpExtensions
     {
+        public static ISymbol? GetDeclaredSymbol(this SemanticModel? semanticModel, AnonymousFunctionExpressionSyntax anonymousFunctionSyntax, CancellationToken cancellationToken = default(CancellationToken))
     }
}

There will be parallel changes to VB.

Usage Examples

Alternative Designs

Risks

[CyrusNajmabadi]

I would support this. But it's worht a discussion. These guys are very funky in that they really can declare entirely fresh symbols (Esp. now with the work for lambda defaults and whatnot), but you have to do GetSymbolInfo on them. The latter does makes sense as these are also expressions though.

Generally speaking though, this divergence has always been odd on the IDE side. We generally have had to constantly special case these guys, rather than uniformly going through GetDeclaredSymbol. It has felt weird that virtually all other type/member symbols that come from something in source use a one mechanism, but these use another.

I'm curious what compiler thinks though. That said, i'm guessing IDE is more the primary consumer of these APIs, so maybe we defer more to that need?

[333fred]

API Review

• Should we just have GetSymbolInfo be the API you use here?
• We need to investigate the behavior of GetSymbolInfo/GetDeclaredSymbol for:
  • Local functions
  • Anonymous types
  • Tuples
  • Other GetDeclaredSymbol examples that are not suffixed with "DeclarationSyntax"
• Do any of them return info from both of these APIs?