Add extraInit and buildJdk args

app/src/dist/share/gradle-env.nix

@@ -21,13 +21,23 @@
 
 { stdenv, buildEnv, fetchurl, gradleGen, writeText, writeTextDir }:
 
-{ envSpec
+{
+# Path to the environment spec generated by gradle2nix (e.g. gradle-env.json).
+  envSpec
 , pname ? null
 , version ? null
 , enableParallelBuilding ? true
+# Arguments to Gradle used to build the project in buildPhase.
 , gradleFlags ? [ "build" ]
+# Gradle package to use instead of the one generated by gradle2nix.
 , gradlePackage ? null
+# Enable debugging for the Gradle build; this will cause Gradle to run a debug server
+# and wait for a JVM debugging client to attach.
 , enableDebug ? false
+# Additional code to run in the Gradle init script (init.gradle).
+, extraInit ? ""
+# Override the default JDK used to run Gradle itself.
+, buildJdk ? null
 , ... } @ args:
 
 let
@@ -243,6 +253,8 @@ let
               }
           }
         ''}
+
+        ${extraInit}
       '';
 
   mkGradle = gradleSpec:
@@ -277,6 +289,7 @@ let
       --info --full-stacktrace --warning-mode=all \
       ${optionalString enableParallelBuilding "--parallel"} \
       ${optionalString enableDebug "-Dorg.gradle.debug=true"} \
+      ${optionalString (buildJdk != null) "-Dorg.gradle.java.home=${buildJdk.home}"} \
       --init-script ${env.initScript} \
       ${optionalString (env.path != "") ''-p "${env.path}"''} \
       ${concatStringsSep " " flags}
@@ -299,7 +312,7 @@ in stdenv.mkDerivation (args // {
     runHook preBuild
 
     (
-    set -x
+    set -eux
 
     # use the init script here
     TMPHOME=$(mktemp -d)