From 03ee759b02f6995e135e120fabec41e9ee870be0 Mon Sep 17 00:00:00 2001
From: novenary <novenary@kwak.zip>
Date: Sun, 9 Feb 2025 17:45:16 +0200
Subject: [PATCH] Build custom JRE package

The default minimal JRE in nixpkgs:
- doesn't work, because it doesn't include enough modules
- is based on the full JDK rather than headless, bringing in unnecessary
  dependencies

Build our own to remedy this.
---
 jre.nix      | 34 ++++++++++++++++++++++++++++++++++
 packages.nix | 10 ++++++----
 2 files changed, 40 insertions(+), 4 deletions(-)
 create mode 100644 jre.nix

diff --git a/jre.nix b/jre.nix
new file mode 100644
index 0000000..1f8caba
--- /dev/null
+++ b/jre.nix
@@ -0,0 +1,34 @@
+{
+  stdenv,
+  jdk17_headless,
+  lib,
+  callPackage,
+}: let
+  jdk = jdk17_headless;
+in
+  stdenv.mkDerivation {
+    pname = "${jdk.pname}-minimal-jre";
+    version = jdk.version;
+
+    buildInputs = [jdk];
+
+    dontUnpack = true;
+
+    # Strip more heavily than the default '-S', since if you're
+    # using this derivation you probably care about this.
+    stripDebugFlags = ["--strip-unneeded"];
+
+    buildPhase = ''
+      runHook preBuild
+
+      mkdir modpath
+      ln -s ${jdk}/lib/openjdk/jmods/* modpath
+      # jpackage includes path references to the base JDK in some native binaries
+      rm modpath/jdk.jpackage.jmod
+      jlink --module-path modpath --add-modules ALL-MODULE-PATH --compress=2 --output $out
+
+      runHook postBuild
+    '';
+
+    dontInstall = true;
+  }
diff --git a/packages.nix b/packages.nix
index bd4b1c1..2bb1673 100644
--- a/packages.nix
+++ b/packages.nix
@@ -129,10 +129,12 @@ lib.makeScope newScope (
     pack-hardmode = self.pack.override {difficulty = "hardmode";};
     pack-expert = self.pack.override {difficulty = "expert";};
 
+    jre = callPackage ./jre.nix {};
+
     forgeServer = callPackage ({
       stdenvNoCC,
       fetchurl,
-      jre17_minimal,
+      jre,
     }:
       stdenvNoCC.mkDerivation (finalAttrs: {
         pname = "forge-server";
@@ -141,7 +143,7 @@ lib.makeScope newScope (
         outputHashMode = "recursive";
         outputHash = "sha256-kZlxL54b/PZGdrxnN3U4NrgixRKN1eqwZ4TeRKvSpYw=";
 
-        nativeBuildInputs = [jre17_minimal];
+        nativeBuildInputs = [jre];
 
         src = fetchurl {
           url = "https://maven.minecraftforge.net/net/minecraftforge/forge/${finalAttrs.version}/forge-${finalAttrs.version}-installer.jar";
@@ -171,7 +173,7 @@ lib.makeScope newScope (
 
     runServer = callPackage ({
       writeShellApplication,
-      jre17_minimal,
+      jre,
       unsup,
     }:
       writeShellApplication {
@@ -191,7 +193,7 @@ lib.makeScope newScope (
           echo 'eula=true' > eula.txt
           ./forge-server/run.sh --nogui "$@"
         '';
-        runtimeInputs = [jre17_minimal];
+        runtimeInputs = [jre];
       }) {};
   }
 )