dotnet/roslyn

Semantic model: Should GetSymbolInfo on `var _` return an IDiscardSymbol?

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#16,316 opened on Jan 7, 2017

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Area-CompilersFeature - TuplesFeature Requesthelp wanted

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Description

Currently, GetSymbolInfo will return null in this case. The only scenario where a discard symbol is returned is with the _ identifier/expression.

   [Fact]
        public void VariousDiscardsInForeach()
        {
            var source =
@"
class C
{
    static void Main()
    {
        foreach ((var _, int _, _, var (_, _), int x) in new[] { (1L, 2, 3, (""hello"", 5), 6) })
        {
            System.Console.Write(x);
        }
    }
}
";
            var comp = CreateCompilationWithMscorlib(source, options: TestOptions.DebugExe, references: s_valueTupleRefs);
            var tree = comp.SyntaxTrees.First();
            var model = comp.GetSemanticModel(tree);

            var discard1 = GetDiscardDesignations(tree).First();
            Assert.Null(model.GetSymbolInfo(declaration1).Symbol); // should return a discard symbol instead?
        }

FYI @AlekseyTs @gafter Related to https://github.com/dotnet/roslyn/pull/16153

Contributor guide

Research direction
Investigate the GetSymbolInfo method in the semantic model to determine if it should return an IDiscardSymbol for var in tuple deconstruction. Check related PR #16153 and the implementation of GetSymbolInfo for discard patterns.
Tech stack
csharp
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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Active
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Clear
Prerequisites
C#Roslyn API
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50