Dune: Change in `dune exec` incantation

[bobbypriambodo]

Hi, I'm currently updating my Dune introduction article with Dune v1.0.1 from Jbuilder 1.0+beta19. I noticed there is a different behavior in dune exec command.

The simplest example would be the hello world example from the docs. Previously with jbuilder, the following works:

$ jbuilder build hello_world.exe
$ jbuilder exec hello_world.exe
Hello, world!

However, with Dune:

$ dune build hello_world.exe
$ dune exec hello_world.exe
Error: Program "hello_world.exe" not found!

As noted in the docs, it works if we use dune exec ./hello_world.exe.

However, if we move the dune and hello_world.ml files to a directory, say bin, the following works:

$ mkdir bin
$ mv dune hello_world.ml bin/
$ dune clean
$ dune exec bin/hello_world.exe
Hello, world!

I thought it should also be dune exec ./bin/hello_world.exe (although this works too). I was wondering if this distinction is intentional.

[jeremiedimino]

The criterion is the same as in a shell:

• a command name without / is searched in the path
• a command name with at least one / is considered as a filename relative to the current directory

The old behavior wasn't intentional. That said, maybe we could always add the current directory to the search path.

[bobbypriambodo]

I see, so the current behavior is the desired one? An issue that I think may happen is that things will break if people depend on the previous behavior in their build scripts (and not using the alias, e.g. @install).

[jeremiedimino]

Yes. However, AFAIR we never discussed the possibility of allowing dune exec hello.exe. Allowing it seems fine to me.

[rgrinberg]

To be honest, I'd rather us error in this case and give the user a useful suggestion. Keeping the semantics clear seems much more important to me.

[voodoos]

I discussed with @emillon and if everyone agrees with that solution I am going to work on adding some useful hints for the misled users.