depext installation failure results in error code 0 #6488
Description
When the command to install only depexts fails, the shell command produces an error code 0, not classifying it as an error. For example, on ocaml-cohttp, this is what happens:
$ opam install ./ --depext-only --with-test --with-doc
[NOTE] Package cohttp-lwt-unix is already installed (current version is 6.1.0).
[NOTE] Package cohttp-lwt is already installed (current version is 6.1.0).
[NOTE] Package cohttp is already installed (current version is 6.1.0).
[NOTE] Package http is already installed (current version is 6.1.0).
[ERROR] Package conflict!
* No agreement on the version of ocaml-base-compiler:
- (invariant) -> ocaml-base-compiler >= 5.3.0
- cohttp-async -> ocaml < 5.3.0 -> ocaml-base-compiler < 5.2.2~
You can temporarily relax the switch invariant with `--update-invariant'
* Incompatible packages:
- (invariant) -> ocaml-base-compiler >= 5.3.0
- cohttp-async -> ocaml < 5.3.0 -> dkml-base-compiler
* Incompatible packages:
- (invariant) -> ocaml-base-compiler >= 5.3.0
- cohttp-async -> ocaml < 5.3.0 -> ocaml-system >= 3.09.1
* Incompatible packages:
- (invariant) -> ocaml-base-compiler >= 5.3.0
- cohttp-async -> ocaml < 5.3.0 -> ocaml-variants
* Missing dependency:
- cohttp-async -> ocaml < 5.3.0 -> ocaml-variants -> xenbigarray
unknown package
* Missing dependency:
- cohttp-async -> ocaml < 5.3.0 -> ocaml-variants -> ocaml-beta
unmet availability conditions: 'enable-ocaml-beta-repository'
* Missing dependency:
- cohttp-async -> ocaml < 5.3.0 -> ocaml-variants -> system-msvc
unmet availability conditions: 'os = "win32"'
And looking at the error code:
$ echo $?
0
It would be useful if opam could classify this as an error and assign an error code.