ocaml-src 4.13.1

Error log

The package failed to build. The error log from opam follows.

Opam plugin "depext" may require upgrading/reinstalling. Reinstall the plugin on the current switch? [Y/n] y
The following actions will be performed:
  - recompile opam-depext 1.2.3

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
-> retrieved opam-depext.1.2.3  (cached)
-> removed   opam-depext.1.2.3
-> installed opam-depext.1.2.3
Done.

<><> opam-depext.1.2.3 installed successfully <><><><><><><><><><><><><><><><><>
=> opam-depext is unnecessary when used with opam >= 2.1. Please use opam install directly instead
# Run eval $(opam env) to update the current shell environment

<><> Carrying on to "opam depext -viy ocaml-src.4.13.1" <><><><><><><><><><><><>

Since version 2.1, opam now handles external dependencies alongside OCaml ones, and the `depext` plugin interface is provided for backwards compatibility only. Consider using your usual `opam install` command to install both OCaml and system dependencies, or `opam install <pkg> --depext-only` if you want to only install external dependencies.
# Detecting depexts using vars: arch=x86_64, os=linux, os-distribution=debian, os-family=debian
[ERROR] No solution for ocaml-src.4.13.1:   * No agreement on the version of ocaml:
            - (invariant) -> ocaml-base-compiler = 5.1.1 -> ocaml = 5.1.1
            - ocaml-src = 4.13.1 -> ocaml = 4.13.1
            You can temporarily relax the switch invariant with `--update-invariant'


Command failed: opam --cli=2.1 list --readonly --external '--resolve=ocaml-src.4.13.1' --color=never returned 20