@atomic setfield! parsing

[MilesCranmer]

I think it would be nice if

@atomic setfield!(var, field, val)
@atomic setproperty!(var, field, val)

expanded correctly or gave a more descriptive error message. I have a custom setproperties! where I wanted to use :atomic on special handling of the setfield! operation and get confused about this because the error shows:

julia> mutable struct A
           @atomic a::Int
       end

julia> a = A(1)
A(1)

julia> @atomic setfield!(a, :a, 2)
ERROR: LoadError: could not parse @atomic expression setfield!(a, :a, 2)

I figured it out after reading https://gist.github.com/vtjnash/11b0031f2e2a66c9c24d33e810b34ec0 that I can provide :sequentially_consistent manually.

[vtjnash]

I don't know how you could, since that call syntax is already defined to mean an atomic update of the first argument expression (e.g. of a). Either as a field update (currently implemented now):

julia> @macroexpand @atomic +(x.x, 1)
:(Base.modifyproperty!(x, :x, +, 1, :sequentially_consistent))

Or a variable update (not yet implemented):

julia> @macroexpand @atomic +(a, 1)
:(Base.modifyglobal!(Main, :a, +, 1, :sequentially_consistent))

# other equivalent expressions would include:
julia> @macroexpand @atomic a + 1
julia> @macroexpand @atomic a += 1