syntax: "..." expression outside call

[damiendr]

Splatting a tuple inside of a tuple literal, and then destructuring the result confuses the parser:

julia> idx = (1,)
(1,)

julia> u = (idx...,)
(1,)

julia> (v,) = (idx...,)
ERROR: syntax: "..." expression outside call

julia> (v,) = tuple(idx...,)
(1,)

julia> (v,) = [idx...,]
1-element Array{Int64,1}:
 1

This trips up @fastmath in the following example:

julia> a = zeros(1); b = zeros(1);

julia> a[idx...] += b[idx...]
0.0

julia> @fastmath a[idx...] += b[idx...]
ERROR: syntax: "..." expression outside call

julia> macroexpand(:(@fastmath a[idx...] += b[idx...]))
quote  # fastmath.jl, line 109:
    ##685 = a # fastmath.jl, line 110:
    (##686,) = (idx...,) # fastmath.jl, line 111:
    ##685[##686] = Base.FastMath.add_fast(##685[##686], b[idx...])
end