C# out param is not reported as an error in visual studio if a local function is called.

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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[severity:It's more difficult to complete my work]
I have attached a minimum reproducible project.
Notice the out method called 'bug' can compile even though the out parameter is not set.

The whole function:

    /// <summary>this compiles and it should not.</summary>
    static void bug(out int a)
    {
        bool hasLevel() => true;
        hasLevel();
    }

OutBug.zip

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Original Comments

Feedback Bot on 8/20/2023, 06:54 PM:

(private comment, text removed)

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Original Solutions

(no solutions)

[jcouv]

This issue was also reported in #70391 (comment) and @SirCxyrtyx offered some details on investigation there.

[SirCxyrtyx]

Bug appears to have been introduced in 0ffa3fa.

That same commit also introduced the PrimaryConstructors_15 flow analysis test, which seems to be quite flawed?

roslyn/src/Compilers/CSharp/Test/Emit2/FlowAnalysis/RegionAnalysisTests.cs

Line 10780 in fe6cc3e

public void PrimaryConstructors_15()

For this code:

class B(out int x)
{
    int X() => x = 1;
}

It asserts that x is definitely assigned on entry to X(), (which it isn't). I'm not sure why data flow analysis of this situation is being tested at all tbh, since a primary constructor out param cannot be accessed from a method.

[jcouv]

Assigned to @AlekseyTs as it looks like this changed due to primary constructor work