why3-ide 1.2.0

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 why3-ide.1.2.0 why3.1.2.0 ocamlfind.1.9.6 ocamlbuild.0.15.0 num.1.5-1 menhir.20190924 lablgtk.2.18.13 dune.3.16.0 conf-pkg-config.3 conf-gtksourceview.2 conf-gtk2.1 camlp-streams.5.0.1" 

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 why3-ide.1.2.0 & why3.1.2.0 & ocamlfind.1.9.6 & ocamlbuild.0.15.0 & num.1.5-1 & menhir.20190924 & lablgtk.2.18.13 & dune.3.16.0 & conf-pkg-config.3 & conf-gtksourceview.2 & conf-gtk2.1 & camlp-streams.5.0.1:   * 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-ide.1.2.0,why3.1.2.0,ocamlfind.1.9.6,ocamlbuild.0.15.0,num.1.5-1,menhir.20190924,lablgtk.2.18.13,dune.3.16.0,conf-pkg-config.3,conf-gtksourceview.2,conf-gtk2.1,camlp-streams.5.0.1' --color=never returned 20