Deprecate calling thunks like functions

[oschulz]

Always use unthunk instead.

Closes #374 .

[mzgubic]

Thanks for the PR! Have you checked if there are any references to calling thunks in the docs?

Let me know once you are happy so I can merge

[mzgubic]

Could we just replace both of these with

function (x::AbstractThunk)()
    Base.depwarn("`(x::AbstractThunk)()`` is deprecated, use `unthunk(x)`", :call_AbstractThunk)
    return unthunk(x)
end

?

Also, BlueStyle.jl uses explicit return

[oschulz]

You mean, use AbstractThunk in the depwarn message for both of them?

[mzgubic]

Good point, should have been something like

function (x::T)() where T <: AbstractThunk
    Base.depwarn("`(x::T)()`` is deprecated, use `unthunk(x)`", :call_AbstractThunk)
    return unthunk(x)
end

[oschulz]

I don't think we can do that - ChainRulesCore is backward compatible with Julia v1.0, and (x::AbstractThunk)() = ... would require >= v1.3, right? And (x::T)() where T <: AbstractThunk = ... even v1.6 won't allow.

[mzgubic]

Thanks for checking 1.0. With the risk of belabouring the idea:

for T in (:Thunk, :InplaceableThunk)
    @eval function (x::$T)()
        Base.depwarn("`(x::" * string($T) * ")()` is deprecated, use `unthunk(x)`", Symbol(:call_, $(T))) 
        return unthunk(x)
    end    
end

should work. Feel free to ignore if you think that the current way is better (but please do add return)

[oschulz]

Sure - just updated the PR, using this variant.

[mzgubic]

Should we also test InplaceableThunk?

[oschulz]

Should we also test InplaceableThunk?

Well, we didn't before, but I can add it.

[oschulz]

Have you checked if there are any references to calling thunks in the docs?

I hope I found and changed all of them ...