Incorrect diagnostic that Deconstruct method is unused.

[gafter]

Roslyn reports that Deconstruct is unused in the C# code below. But it is used. You would get an error if you remove the method.

class C
{
    void M(
        ref object o,
        ref object p)
    {
        (o, p) = this;
    }
    
    void Deconstruct(
        out object? o,
        out object? p)
    {
        o = null;
        p = null;
    }
}

[CyrusNajmabadi]

@gafter are you getting a compiler warning, or an analyzer warning? If so, can you include the diagnostic id?

[gafter]

I don't know. See https://sharplab.io/#v2:CYLg1APgAgTABAYQLACgDeq5blALHAWQApNsyAnAUwDM4B7AIwCtKBjAF3oBpSysrajFhzgAHAJS84GFH2xE6XMeLgBeOOwAWASwDOAbikBfKVLxwAImzoA7Xe3IBXDiVlz6jzkLbsA/NykyOk96Zh9/CSkZd3o1OBtHABtEwzc5UTiE5NSyExQ8oA==

I think it's a compiler informational message.

[jcouv]

I see that diagnostic too (IDE0051)

[CyrusNajmabadi]

@jcouv I can't figure out how to determine that the .Deconstruct method is used here. How is this exposed in teh semantic model? Also checking with @333fred . I do see a IDeconstructAssignmentOperation, but it seems to be missing the target method, unless i'm missing something. Could you guys advise? How do you encode this into the tree?

[jcouv]

There's an issue tracking adding this information to IDeconstructAssignmentOperation: #74757
Otherwise, GetDeconstructionInfo and GetDeconstructionInfo on semantic model currently should have the information.