emacs.pkgs.ghostel: ease overrideAttrs of local bumps

To make overrideAttrs pleasant, we should merge the elisp derivation
and the zig module derivation into one derivation.  One way is to make
zig build hooks composable via #514028.

This patch tries to make overrideAttrs less painful based on the
current situation.  With this patch, overrideAttrs can be done like
this:

emacs.pkgs.ghostel.overrideAttrs (old: {
  version = "0.41.0";
  src = old.src.override {
    hash = "sha256-07Ml/eRIHyptI6MNlHhDNsfIiXOAUVKaEalDVJ101WM=";
  };
  zigDeps = old.zigDeps.overrideAttrs {
    outputHash = "sha256-lFU0ywNyP1q2NL9MkIfWciH03VAA/Act5dGYAV4V7EY=";
  };
})

pkgs/applications/editors/emacs/elisp-packages/manual-packages/ghostel/package.nix

@@ -12,6 +12,46 @@
 let
   zig = zig_0_15;
 
+  mkModule =
+    {
+      pname,
+      version,
+      src,
+      zigDeps,
+    }:
+    stdenv.mkDerivation (finalAttrs: {
+      inherit
+        pname
+        version
+        src
+        zigDeps
+        ;
+
+      nativeBuildInputs = [ zig ] ++ lib.optionals stdenv.hostPlatform.isDarwin [ xcbuild ];
+
+      env.EMACS_INCLUDE_DIR = "${emacs}/include";
+
+      dontSetZigDefaultFlags = true;
+
+      doCheck = true;
+
+      zigCheckFlags = [
+        "-Dcpu=baseline"
+        # See https://github.com/ghostty-org/ghostty/blob/main/PACKAGING.md#build-options
+        "-Doptimize=ReleaseFast"
+      ];
+
+      zigBuildFlags = finalAttrs.zigCheckFlags;
+
+      postConfigure = ''
+        cp -rLT ${finalAttrs.zigDeps} "$ZIG_GLOBAL_CACHE_DIR/p"
+        chmod -R u+w "$ZIG_GLOBAL_CACHE_DIR/p"
+      '';
+    });
+
+  libExt = stdenv.hostPlatform.extensions.sharedLibrary;
+in
+melpaBuild (finalAttrs: {
   pname = "ghostel";
 
   version = "0.44.0";
@@ -19,60 +59,37 @@ let
   src = fetchFromGitHub {
     owner = "dakra";
     repo = "ghostel";
-    tag = "v${version}";
+    tag = "v${finalAttrs.version}";
     hash = "sha256-vRGZoQtjsL42ga07fOfEjccKRidAhqgwHBoKs++62Ls=";
   };
 
-  module = stdenv.mkDerivation (finalAttrs: {
-    inherit pname version src;
-
-    zigDeps = zig.fetchDeps {
-      inherit (finalAttrs) src pname version;
-      fetchAll = true;
-      hash = "sha256-yrVgiofdmVjTGJ+PGPGRCc8gb/JcEca1uAzIoPgHHqU=";
-    };
-
-    nativeBuildInputs = [ zig ] ++ lib.optionals stdenv.hostPlatform.isDarwin [ xcbuild ];
-
-    env.EMACS_INCLUDE_DIR = "${emacs}/include";
-
-    dontSetZigDefaultFlags = true;
-
-    doCheck = true;
-
-    zigCheckFlags = [
-      "-Dcpu=baseline"
-      # See https://github.com/ghostty-org/ghostty/blob/main/PACKAGING.md#build-options
-      "-Doptimize=ReleaseFast"
-    ];
-
-    zigBuildFlags = finalAttrs.zigCheckFlags;
-
-    postConfigure = ''
-      cp -rLT ${finalAttrs.zigDeps} "$ZIG_GLOBAL_CACHE_DIR/p"
-      chmod -R u+w "$ZIG_GLOBAL_CACHE_DIR/p"
-    '';
-  });
-
-  libExt = stdenv.hostPlatform.extensions.sharedLibrary;
-in
-melpaBuild {
-  inherit pname version src;
+  # this can be put into mkModule, but we put it here to ease user overrideAttrs
+  zigDeps = zig.fetchDeps {
+    inherit (finalAttrs) src pname version;
+    fetchAll = true;
+    hash = "sha256-yrVgiofdmVjTGJ+PGPGRCc8gb/JcEca1uAzIoPgHHqU=";
+  };
 
   files = ''
     (:defaults "etc" "ghostel-module${libExt}" "ghostel-module.version")
   '';
 
   preBuild = ''
-    install ${module}/ghostel-module${libExt} ghostel-module${libExt}
-    install --mode=444 ${module}/ghostel-module.version ghostel-module.version
+    install ${finalAttrs.finalPackage.module}/ghostel-module${libExt} ghostel-module${libExt}
+    install --mode=444 ${finalAttrs.finalPackage.module}/ghostel-module.version ghostel-module.version
   '';
 
   passthru = {
     updateScript = nix-update-script { };
 
-    inherit module;
-    inherit (module) zigDeps;
+    module = mkModule {
+      pname = "${finalAttrs.pname}-module";
+      inherit (finalAttrs)
+        version
+        src
+        zigDeps
+        ;
+    };
   };
 
   meta = {
@@ -84,4 +101,4 @@ melpaBuild {
     ];
     license = lib.licenses.gpl3Plus;
   };
-}
+})