why3 1.2.1

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 frama-c.20.0 zarith.1.14 yojson.2.2.2 why3.1.2.1 seq.base psmt2-frontend.0.1 ocplib-simplex.0.4.1 ocamlgraph.1.8.8 ocamlfind.1.9.6 ocamlbuild.0.15.0 num.1.5-1 menhir.20190924 lablgtk.2.18.13 host-arch-x86_64.1 dune.3.16.0 conf-zlib.1 conf-pkg-config.3 conf-gtksourceview.2 conf-gtk2.1 conf-gnomecanvas.2 conf-gmp.4 conf-autoconf.0.2 camlzip.1.12 camlp-streams.5.0.1 alt-ergo-free.2.2.0" 

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 frama-c.20.0 & zarith.1.14 & yojson.2.2.2 & why3.1.2.1 & seq.base & psmt2-frontend.0.1 & ocplib-simplex.0.4.1 & ocamlgraph.1.8.8 & ocamlfind.1.9.6 & ocamlbuild.0.15.0 & num.1.5-1 & menhir.20190924 & lablgtk.2.18.13 & host-arch-x86_64.1 & dune.3.16.0 & conf-zlib.1 & conf-pkg-config.3 & conf-gtksourceview.2 & conf-gtk2.1 & conf-gnomecanvas.2 & conf-gmp.4 & conf-autoconf.0.2 & camlzip.1.12 & camlp-streams.5.0.1 & alt-ergo-free.2.2.0:   * 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=frama-c.20.0,zarith.1.14,yojson.2.2.2,why3.1.2.1,seq.base,psmt2-frontend.0.1,ocplib-simplex.0.4.1,ocamlgraph.1.8.8,ocamlfind.1.9.6,ocamlbuild.0.15.0,num.1.5-1,menhir.20190924,lablgtk.2.18.13,host-arch-x86_64.1,dune.3.16.0,conf-zlib.1,conf-pkg-config.3,conf-gtksourceview.2,conf-gtk2.1,conf-gnomecanvas.2,conf-gmp.4,conf-autoconf.0.2,camlzip.1.12,camlp-streams.5.0.1,alt-ergo-free.2.2.0' --color=never returned 20