Interaction of setenv and cmd interpolation

[Keno]

I think interpolating a cmd that had its env set should either raise an error or propagate the environment. Current behavior:

julia> c = setenv(`x`, "A"=>true)
setenv(`x`,String["A=true"])

julia> `$c`
`x`

[Keno]

Just ran into this again. We missed 1.0 of course, but marking for triage on what to do here.

[Keno]

Quick discussion with @JeffBezanson, one possible solution may be to allow interpolation in first position, but make it an error everywhere else.

[vtjnash]

Also, by setenv, I assume we mean, "all keyword args to the Cmd constructor (ignorestatus, env, dir, detach, windows_verbatim, windows_hide, flags)"

[StefanKarpinski]

Triage decision:

• if a command with environment is spliced into the first position in another command, then we should propagate the environment
• if a command with environment is spliced into another command anywhere else, then it should be an error since we can't know what was intended