Expected Behavior

I would expect dune exec ./main.exe to be equivalent to dune build ./main.exe && _build/default/main.exe (assuming main.ml is at the root).

(dune exec --help says that it should actually be equivalent to dune install; COMMAND, which is close enough.)

Actual Behavior

• Filename.get_temp_file_name returns something like /tmp/build_596b2c_dune instead of /tmp.
• Moreover, this temporary directory seems to be deleted after the process exits. This is a breaking change for the --keep-temp flag of Tezt.
• Sys.argv.(0) is an absolute path (it used to typically be relative, starting with _build). This broke Tezt's cram tests in a way that is hard to fix for both Dune 3.19.0 and Dune 3.18.2.
• Some other environment variables are modified (but this was already the case before 3.19.0 so this is out of scope for this issue — in case you're curious, this breaks this script in some cases).

I would suggest to at least document those changes in the changelog. The absolute path is probably not worth a fix, but the behavior of the temporary directory is puzzling.

Maybe 2603202 fixes some of the issues, but I failed to compile Dune (I tried something like ./configure && make bootstrap && make install, the latter step failed because of a lack of .install; and make release failed with an uncaught Not_found).

Reproduction

main.ml:

let () =
  Printf.printf "argv0 = %S\n%!" Sys.argv.(0);
  let tmp = Filename.get_temp_dir_name () in
  Printf.printf "tmp = %S\n%!" tmp;
  let ch = open_out (Filename.concat tmp "dune-test") in
  close_out ch

dune:

(executable (name main))

dune-project:

(lang dune 3.19)

Then run:

dune exec ./main.exe
ls /tmp/build*dune

For instance, I got:

cd /tmp/abc/ && dune exec ./main.exe && ls /tmp/build*dune
argv0 = "/tmp/abc/_build/default/main.exe"
tmp = "/tmp/build_596b2c_dune"
zsh:1: no matches found: /tmp/build*dune

Specifications

• Version of dune (output of dune --version): 3.19.0
• Version of ocaml (output of ocamlc --version): 5.2.1
• Operating system (distribution and version): Debian testing

Additional information

• Link to gist with verbose output (run dune with the --verbose flag): (none)