confusing dependency error message (what is the meaning of '→'?)

[sanette]

Hi

trying to install (for instance) tsdl.0.9.8 on ocaml 5.2:

$ opam install tsdl.0.9.8
[ERROR] Package conflict!
  * No agreement on the version of ocaml:
    - (invariant) → ocaml-base-compiler = 5.2.0 → ocaml = 5.2.0
    - tsdl = 0.9.8 → ctypes < 0.21.0 → ocaml < 4.03.0

Looking up ctypes.0.20.1 I see

depends      "ocaml" {>= "4.03.0" & < "5.2"}

which explains why it won't install on ocaml 5.2. But what is the meaning of the message
- tsdl = 0.9.8 → ctypes < 0.21.0 → ocaml < 4.03.0 ? Requiring ocaml < 4.03 is absurd, since it will work fine with (for instance) ocaml 5.0.
I find this quite confusing

<include here the output of `opam config report`, if applicable>
# opam config report
# opam-version         2.2.1
# self-upgrade         no
# system               arch=x86_64 os=linux os-distribution=neon os-version=22.04
# solver               builtin-mccs+glpk
# install-criteria     -removed,-count[avoid-version,changed],-count[version-lag,request],-count[version-lag,changed],-count[missing-depexts,changed],-changed
# upgrade-criteria     -removed,-count[avoid-version,changed],-count[version-lag,solution],-count[missing-depexts,changed],-new
# jobs                 3
# repositories         1 (http), 1 (local), 2 (version-controlled) (default repo at 0496562931aba14e8095ac8eaf3bf067c2ed18a6)
# pinned               0
# current-switch       5.2.0
# invariant            ocaml-base-compiler = 5.2.0 | ocaml-system = 5.2.0
# compiler-packages    ocaml-base-compiler.5.2.0, ocaml-options-vanilla.1
# ocaml:native         true
# ocaml:native-tools   true
# ocaml:native-dynlink true
# ocaml:stubsdir       /home/san/.opam/5.2.0/lib/ocaml/stublibs:/home/san/.opam/5.2.0/lib/ocaml
# ocaml:preinstalled   false
# ocaml:compiler       5.2.0

[kit-ty-kate]

The meaning of the arrow is "depends on", however this is indeed a bug to the way this is displayed, but it has been fixed in #6106 and is available in opam 2.3.0~alpha1.

If you want to test the alpha you can do so using:

bash -c "sh <(curl -fsSL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh) --version 2.3.0~alpha1"

Since this is already fixed, i'll close this as a duplicate of #4373. Thanks for the report

[sanette]

thanks! I'm sorry I didn't see this was a duplicate

Indeed the new opam 2.3.0~alpha1 has a good error message:

 $ opam install tsdl.0.9.8
[ERROR] Package conflict!
  * No agreement on the version of ocaml:
    - (invariant) → ocaml-base-compiler = 5.2.0 → ocaml = 5.2.0
    - tsdl = 0.9.8 → ctypes < 0.21.0 → ocaml < 5.2