dotnet/roslyn

Unclear error message for pointer types in pattern matching

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#43,339 opened on Apr 14, 2020

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Area-CompilersConcept-Diagnostic ClarityFeature - Pattern Matchinghelp wanted

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Description

unsafe class C
{
    static void Main()
    {
        int* ptr = null;
        _ = ptr is var (x); // error CS8521: Pattern-matching is not permitted for pointer types.
        _ = ptr is var y; // valid code
    }
}

The error message shown above doesn't mention anything about parenthesized patterns, despite the fact that that's the only difference between those two lines. We can make this clearer.

Contributor guide

Research direction
Locate the error message CS8521 in the compiler source and modify it to explicitly mention parenthesized 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.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
85