Include doctest and cabal-doctest in the nix develop shell

Author: neilmayhew

flake.nix

@@ -138,7 +138,19 @@
                 (python3.withPackages (ps: with ps; [sphinx sphinx_rtd_theme recommonmark sphinx-markdown-tables sphinxemoji]))
                 haskellPackages.implicit-hie
                 shellcheck
-              ];
+              ] ++
+              (let
+                doctest = haskell-nix.hackage-package {
+                  name = "doctest";
+                  version = "0.24.0";
+                  configureArgs = "-f cabal-doctest";
+                  inherit (config) compiler-nix-name;
+                };
+              in
+                [
+                  (doctest.getComponent "exe:cabal-doctest")
+                  (doctest.getComponent "exe:doctest")
+                ]);
             # disable Hoogle until someone request it
             withHoogle = false;
             # Skip cross compilers for the shell