why3-base 0.85

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 1.2.1-1

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
-> retrieved opam-depext.1.2.1-1  (cached)
-> removed   opam-depext.1.2.1-1
-> installed opam-depext.1.2.1-1
Done.

<><> opam-depext.1.2.1-1 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 why3.0.85 zarith.1.13 why3-base.0.85 stdlib-shims.0.3.0 ocamlgraph.2.0.0 ocamlfind.1.9.6 num.0 lablgtk.2.18.11 dune.3.13.0 conf-zlib.1 conf-pkg-config.3 conf-gtksourceview.2 conf-gtk2.1 conf-gmp.4 camlzip.1.10 base-num.base" 

You are using opam 2.1+, where external dependency handling has been integrated: consider calling opam directly, the 'depext' plugin interface is provided for backwards compatibility only
# Detecting depexts using vars: arch=x86_64, os=linux, os-distribution=debian, os-family=debian
[ERROR] No solution for why3.0.85 & zarith.1.13 & why3-base.0.85 & stdlib-shims.0.3.0 & ocamlgraph.2.0.0 & ocamlfind.1.9.6 & num.0 & lablgtk.2.18.11 & dune.3.13.0 & conf-zlib.1 & conf-pkg-config.3 & conf-gtksourceview.2 & conf-gtk2.1 & conf-gmp.4 & camlzip.1.10 & base-num.base:   * Missing dependency:
            - conf-gtksourceview
            depends on the unavailable system package 'libgtksourceview2.0-dev'. Use `--no-depexts' to attempt installation anyway, or it is possible that a depext package name in the opam file is incorrect.


Command failed: opam --cli=2.1 list --readonly --external '--resolve=why3.0.85,zarith.1.13,why3-base.0.85,stdlib-shims.0.3.0,ocamlgraph.2.0.0,ocamlfind.1.9.6,num.0,lablgtk.2.18.11,dune.3.13.0,conf-zlib.1,conf-pkg-config.3,conf-gtksourceview.2,conf-gtk2.1,conf-gmp.4,camlzip.1.10,base-num.base' returned 20