@kwdef doesn't allow @atomic fields with default values

[JamesWrigley]

MWE:

julia> @kwdef mutable struct Foo
           @atomic x::Int
       end
Foo

julia> @kwdef mutable struct Bar
           @atomic x::Int = 1
       end
ERROR: LoadError: @atomic modify expression missing field access
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] make_atomic(order::Any, a1::Any, op::Any, a2::Any)
   @ Base ./expr.jl:1240
 [3] make_atomic(order::Any, ex::Any)
   @ Base ./expr.jl:1232
 [4] var"@atomic"(__source__::LineNumberNode, __module__::Module, ex::Any)
   @ Base ./expr.jl:1190
 [5] #macroexpand#74
   @ ./expr.jl:125 [inlined]
 [6] macroexpand(m::Module, x::Any)
   @ Base ./expr.jl:123
 [7] var"@kwdef"(__source__::LineNumberNode, __module__::Module, expr::Any)
   @ Base ./util.jl:564
in expression starting at REPL[3]:1

The exception is coming from here where the struct expression is expanded:

julia/base/util.jl

Line 582 in 8e9c59f

expr = macroexpand(__module__, expr) # to expand @static

To fix this I think the code would need to go through the expr before the macroexpand to remove and record field atomicity, and then insert @atomic for those fields in the generated constructor. Related issue: #45020