Julia: Check isdir(dest) and copy into that directory in cp and friends?

[fredrikekre]

Should we check if "dest" is a directory, and if so, copy "src" to that directory?

julia> mkdir("dest"); touch("src"); cp("src", "dest")
ERROR: ArgumentError: 'dest' exists. `force=true` is required to remove 'dest' before copying.
Stacktrace:
 [1] #checkfor_mv_cp_cptree#10(::Bool, ::Function, ::String, ::String, ::String) at ./file.jl:191
 [2] #checkfor_mv_cp_cptree at ./<missing>:0 [inlined]
 [3] #cp#12(::Bool, ::Bool, ::Nothing, ::Function, ::String, ::String) at ./file.jl:241
 [4] cp(::String, ::String) at ./file.jl:236
 [5] top-level scope

Compare e.g. with

fredrik@fredrik-laptop:~$ mkdir dest && touch src && cp src dest && ls dest
src

[KristofferC]

Adding triage since this changes behavior and probably needs to be decided before 1.0.

[nalimilan]

What do other languages do? I would think it's reasonable to be stricter in a programming language than in the shell, which allows catching potential mistakes.

[fredrikekre]

Just noting also that the current behaviour is not very useful; it is unlikely that you want to replace a folder with a file (which is the result of setting force = true in the call above), and that, what you currently have to do

cp("src", joinpath(dir, "src"))

is not very nice.

[mbauman]

Python has both copyfile (with our current semantics) and copy (which supports directory targets). Ruby is similar with copy_file and cp.

[martinholters]

Would cp(src, into=dir) be a good API here?

[JeffBezanson]

I think changing this would be worse in terms of orthogonality --- if you actually want the logic "if this is a directory then copy into it", then you should write that. Conditional behavior should not be built into the library function itself.

[stevengj]

cp(src, into=dir) doesn't seem that much better than cp(src, joinpath(dir, src)). (If somebody needs this function a lot they could always define a cpinto(src, dir) = cp(src, joinpath(dir, src)) function.)

This use-case would have to come up a lot to put this specific functionality in to Base. Grepping Julia packages for uses of cp with joinpath, I see a handful of code that could be marginally shortened with an into= keyword, but it doesn't seem like enough to be worthwhile.