dotnet/roslyn

Spurious use of unassigned variable error with unimplemented partial

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#45,875 opened on Jul 10, 2020

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Area-CompilersBugConcept-Diagnostic Clarityhelp wanted

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Description

public partial class C {
    public partial string M1(string dummyParam, out bool i); // error CS8795: Partial method 'C.M1(string, out bool)' must have an implementation part because it has accessibility modifiers.
    
    public void M2(C c)
    {
        c.M1(null, out bool i);
        _ = i.ToString(); // error CS0165: Use of unassigned local variable 'i'
    }
}

Since this partial method must have an implementation (and we already error on it), we could suppress the error on the use of the unassigned variable.

Contributor guide

Research direction
Find the code in the Roslyn compiler that emits error CS0165 (use of unassigned variable) and add a condition to suppress it when the variable is assigned via an out parameter from a partial method call that lacks an implementation part (which already triggers error CS8795).
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.
Half day
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#compiler internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40