ci: migrate to 'exec' runner

Now that I have written a script to do the Matrix notification, I can do
that.

.drone.yml

@@ -1,24 +1,27 @@
+---
 kind: pipeline
-name: check config
+type: exec
+name: NixOS config check
 
 steps:
-  - name: format check
-    image: nixos/nix
-    commands:
-      - nix-shell -p nixpkgs-fmt --run 'nixpkgs-fmt . --check'
+- name: format check
+  commands:
+  - nix develop -c nixpkgs-fmt .
 
-  - name: notify
-    image: plugins/matrix
-    settings:
-      homeserver:
-        from_secret: matrix_homeserver
-      roomid:
-        from_secret: matrix_roomid
-      username:
-        from_secret: matrix_username
-      password:
-        from_secret: matrix_password
-      trigger:
-        status:
-          - failure
-          - success
+- name: notifiy
+  commands:
+  - nix run .#matrix-notifier
+  environment:
+    ADDRESS:
+      from_secret: matrix_homeserver
+    ROOM:
+      from_secret: matrix_roomid
+    USER:
+      from_secret: matrix_username
+    PASS:
+      from_secret: matrix_password
+  when:
+    status:
+      - failure
+      - success
+...

pkgs/default.nix

@@ -14,6 +14,8 @@ rec {
 
   lohr = pkgs.callPackage ./lohr { };
 
+  matrix-notifier = pkgs.callPackage ./matrix-notifier { };
+
   nolimips = pkgs.callPackage ./nolimips { };
 
   vimix-cursors = pkgs.callPackage ./vimix-cursors { };

pkgs/matrix-notifier/default.nix

@@ -0,0 +1,45 @@
+{ curl, jq, fetchFromGitHub, lib, makeWrapper, stdenvNoCC }:
+stdenvNoCC.mkDerivation rec {
+  pname = "matrix-notifier";
+  version = "0.1.0";
+
+  src = fetchFromGitHub {
+    owner = "ambroisie";
+    repo = "matrix-notifier";
+    rev = "v${version}";
+    sha256 = "sha256-MbtxLUVL4bBS66TJTXky/0blR9lFKzLkRccck7Um2Co=";
+  };
+
+  phases = [ "installPhase" "fixupPhase" ];
+
+  nativeBuildInputs = [
+    makeWrapper
+  ];
+
+  installPhase = ''
+    mkdir -p $out/bin
+    cp $src/${pname} $out/bin/${pname}
+    chmod a+x $out/bin/${pname}
+  '';
+
+  wrapperPath = lib.makeBinPath [
+    curl
+    jq
+  ];
+
+  fixupPhase = ''
+    patchShebangs $out/bin/${pname}
+    wrapProgram $out/bin/${pname} --prefix PATH : "${wrapperPath}"
+  '';
+
+  meta = with lib; {
+    description = ''
+      A very simple bash script that can be used to send a message to
+      a Matrix room
+    '';
+    homepage = "https://gitea.belanyi.fr/ambroisie/${pname}";
+    license = licenses.mit;
+    platforms = platforms.unix;
+    maintainers = with maintainers; [ ambroisie ];
+  };
+}