inconsistencies with assignments in argument lists

[mortenpi]

Assignment in tuples and arrays

julia> x=65; [x,x|=0x20]
2-element Vector{Int64}:
 97
 97

julia> x=65; (x,x|=0x20)
(97, 97)

was made a syntax error at one point (in 0.3; see #4982, #4990 and closing commits), but it's allowed again (not sure if intentionally or not). But it leads to some fun inconsistencies:

julia> value = 1; (value, value + 1, value += 1, value += 1)
(3, 2, 2, 3)

julia> let value = 1; (value, value + 1, value += 1, value += 1); end
(1, 2, 2, 3)

[simeonschaub]

Note that this isn't specific to tuples or arrays, but is the case for any kind of argument list:

julia> x=1; println(x, x+=1)
22

The underlying issue here seems to be that lowering often treats symbols just like SSA-values and doesn't take into account that evaluating other arguments before that symbol could change its value. Here's another fun inconsistency which evaluates differently to the example above:

julia> x=1; println(begin x end, x+=1)
12

@JeffBezanson would you agree with the assessment that this is a lowering bug?

[JeffBezanson]

That's bad, and there is a regression in here somewhere since in 1.0 I get

julia> function f(); global value; value = 1; (value, value + 1, value += 1, value += 1); end

julia> f()
(1, 2, 2, 3)

but (3, 2, 2, 3) in more recent versions.

[gbaraldi]

It seems to have broken in 1.1 already

[mortenpi]

I guess it's perhaps not surprising, but I noticed that this also affects string interpolation:

julia> value = 1; "$(value), $(value + 1), $(value += 1), $(value += 1)"
"3, 2, 2, 3"

julia> let value = 1; "$(value), $(value + 1), $(value += 1), $(value += 1)"; end
"1, 2, 2, 3"

[mgkuhn]

Does Julia make any promises about the order in which function arguments in a function-call expression (or tuple arguments) are evaluated?

C does not.

[JeffBezanson]

Yes, we should evaluate them left to right.