Add conf-allegro5 package

packages/allegro5/allegro5.0.1/opam

@@ -10,6 +10,7 @@ depends: [
   "ocaml"
   "dune" {>= "3.11"}
   "odoc" {with-doc}
+  "conf-allegro5"
 ]
 build: [
   ["dune" "subst"] {dev}
@@ -28,6 +29,12 @@ build: [
   ["dune" "install" "-p" name "--create-install-files" name]
 ]
 dev-repo: "git+https://github.com/Frigory33/ocaml-allegro-5.git"
+post-messages: [
+  """\
+We're sorry that your install failed. Please check in the README.md file
+what minimal version of Allegro this package requires."""
+    {failure}
+]
 url {
   src:
     "https://github.com/Frigory33/ocaml-allegro-5/releases/download/0.1/allegro5-0.1.tbz"

packages/conf-allegro5/conf-allegro5.1/opam

@@ -0,0 +1,40 @@
+opam-version: "2.0"
+maintainer: "allegro-developers@lists.liballeg.org"
+homepage: "https://liballeg.org"
+authors: "The Allegro authors"
+bug-reports: "https://github.com/ocaml/opam-repository/issues"
+license: "Giftware"
+build: ["pkg-config" "allegro-5"]
+depexts: [
+  [
+    "allegro5"
+    "allegro5-addon-image"
+    "allegro5-addon-primitives"
+    "allegro5-addon-ttf"
+  ] {os-distribution = "centos" | os-distribution = "fedora"}
+  [
+    "liballegro-devel"
+    "liballegro_image-devel"
+    "liballegro_primitives-devel"
+    "liballegro_ttf-devel"
+  ] {os-family = "suse" | os-family = "opensuse"}
+  [
+    "liballegro5-dev"
+    "liballegro-image5-dev"
+    "liballegro-primitives5-dev"
+    "liballegro-ttf5-dev"
+  ] {os-family = "debian" | os-family = "ubuntu"}
+  ["allegro5"] {os-distribution = "nixos"}
+  ["allegro"] {os-family = "arch"}
+  ["allegro-dev"] {os-family = "alpine"}
+  ["allegro"] {os-distribution = "homebrew"}
+  ["allegro5"] {os = "freebsd"}
+  ["allegro5"] {os = "netbsd"}
+]
+synopsis: "Virtual package relying on Allegro 5 development libraries"
+description:
+  "This package can only install if Allegro 5 development libraries are accessible through pkg-config."
+depends: [
+  "conf-pkg-config" {build}
+]
+flags: conf