lib: add fetchFrom9Front

pkgs/build-support/fetch9front/default.nix

···
+{ fetchgit, fetchzip, lib }:
+
+lib.makeOverridable (
+  { owner
+  , repo
+  , rev
+  , domain ? "git.9front.org"
+  , name ? "source"
+  , leaveDotGit ? false
+  , deepClone ? false
+  , ... # For hash agility
+  } @ args:
+
+  let
+    passthruAttrs = removeAttrs args [ "domain" "owner" "repo" "rev" "leaveDotGit" "deepClone" ];
+
+    useFetchGit = leaveDotGit || deepClone;
+    fetcher = if useFetchGit then fetchgit else fetchzip;
+
+    gitRepoUrl = "git://${domain}/${owner}/${repo}";
+
+    fetcherArgs = (if useFetchGit then {
+      # git9 does not support shallow fetches
+      inherit rev leaveDotGit;
+      url = gitRepoUrl;
+    } else {
+      url = "https://${domain}/${owner}/${repo}/${rev}/snap.tar.gz";
+
+      passthru = {
+        inherit gitRepoUrl;
+      };
+    }) // passthruAttrs // { inherit name; };
+  in
+
+  fetcher fetcherArgs // { inherit rev; }
+)

pkgs/top-level/all-packages.nix

···
 
   fetchFromGitiles = callPackage ../build-support/fetchgitiles { };
 
+  fetchFrom9Front = callPackage ../build-support/fetch9front { };
+
   fetchFromRepoOrCz = callPackage ../build-support/fetchrepoorcz { };
 
   fetchgx = callPackage ../build-support/fetchgx { };