Move Gradle build logic to a setup hook

nix/build-maven-repo.nix

@@ -0,0 +1,189 @@
+{
+  lib,
+  stdenv,
+  fetchurl,
+  substitute,
+  symlinkJoin,
+}:
+
+{
+  # Path to the lockfile generated by gradle2nix (e.g. gradle.lock).
+  lockFile,
+  # Override functions which fetch dependency artifacts.
+  # Names in this set are URL schemes such as "https" or "s3".
+  # Values are functions which take a dependency in the form
+  # `{ urls, hash }` and fetch into the Nix store. For example:
+  #
+  #   {
+  #     s3 = { name, urls, hash }: fetchs3 {
+  #       s3url = builtins.head urls;
+  #       # TODO This doesn't work without patching fetchs3 to accept SRI hashes
+  #       inherit name hash;
+  #       region = "us-west-2";
+  #       credentials = {
+  #         access_key_id = "foo";
+  #         secret_access_key = "bar";
+  #       };
+  #     };
+  #   }
+  fetchers ? { },
+  # Override artifacts in the offline Maven repository.
+  #
+  # This is an attrset is of the form:
+  #
+  #   {
+  #     "${group}:${module}:${version}" = {
+  #       "${filename}" = <override function>;
+  #     }
+  #   }
+  #
+  # The override function takes the original derivation from 'fetchers' (e.g. the result of
+  # 'fetchurl') and produces a new derivation to replace it.
+  #
+  # Examples:
+  #
+  # 1. Replace a dependency's JAR artifact:
+  #
+  #    {
+  #      "com.squareup.okio:okio:3.9.0"."okio-3.9.0.jar" = _: fetchurl {
+  #        url = "https://repo.maven.apache.org/maven2/com/squareup/okio/okio/3.9.0/okio-3.9.0.jar";
+  #        hash = "...";
+  #        downloadToTemp = true;
+  #        postFetch = "install -Dt $out/com/squareup/okio/okio/3.9.0/ $downloadedFile"
+  #      };
+  #    }
+  #
+  # 2. Patch a JAR containing native binaries:
+  #
+  #    {
+  #      "com.android.tools.build:aapt2:8.5.0-rc02-11315950" = {
+  #        "aapt2-8.5.0-rc02-11315950-linux.jar" = src: runCommandCC src.name {
+  #          nativeBuildInputs = [ jdk autoPatchelfHook ];
+  #          dontAutoPatchelf = true;
+  #        } ''
+  #          cp ${src} aapt2.jar
+  #          jar xf aapt2.jar aapt2
+  #          chmod +x aapt2
+  #          autoPatchelf aapt2
+  #          jar uf aapt2.jar aapt2
+  #          cp aapt2.jar $out
+  #        '';
+  #      }
+  #    }
+  overrides ? { },
+}:
+
+let
+
+  inherit (builtins)
+    attrValues
+    elemAt
+    filter
+    fromJSON
+    getAttr
+    head
+    length
+    mapAttrs
+    replaceStrings
+    ;
+
+  inherit (lib) mapAttrsToList readFile;
+
+  inherit (lib.strings) sanitizeDerivationName;
+
+  toCoordinates =
+    id:
+    let
+      coords = builtins.split ":" id;
+
+      parseVersion =
+        version:
+        let
+          parts = builtins.split ":" version;
+          base = elemAt parts 0;
+        in
+        if length parts >= 2 then
+          let
+            snapshot = elemAt parts 2;
+          in
+          replaceStrings [ "-SNAPSHOT" ] [ "-${snapshot}" ] base
+        else
+          base;
+    in
+    rec {
+      group = elemAt coords 0;
+      module = elemAt coords 2;
+      version = elemAt coords 4;
+      uniqueVersion = parseVersion version;
+    };
+
+  fetchers' = {
+    http = fetchurl;
+    https = fetchurl;
+  } // fetchers;
+
+  fetch =
+    coords: overrides: name:
+    { url, hash }:
+    let
+      scheme = head (builtins.match "([a-z0-9+.-]+)://.*" url);
+      fetch' = getAttr scheme fetchers';
+      artifact = fetch' { inherit url hash; };
+      override = overrides.name or lib.id;
+    in
+    override artifact;
+
+  mkModule =
+    id: artifacts:
+    let
+      coords = toCoordinates id;
+      modulePath = "${replaceStrings [ "." ] [ "/" ] coords.group}/${coords.module}/${coords.version}";
+      moduleOverrides = overrides.${id} or { };
+    in
+    stdenv.mkDerivation {
+      pname = sanitizeDerivationName "${coords.group}-${coords.module}";
+      version = coords.uniqueVersion;
+
+      srcs = mapAttrsToList (fetch coords moduleOverrides) artifacts;
+
+      dontPatch = true;
+      dontConfigure = true;
+      dontBuild = true;
+      dontFixup = true;
+      dontInstall = true;
+
+      preUnpack = ''
+        mkdir -p "$out/${modulePath}"
+      '';
+
+      unpackCmd = ''
+        cp "$curSrc" "$out/${modulePath}/$(stripHash "$curSrc")"
+      '';
+
+      sourceRoot = ".";
+
+      preferLocalBuild = true;
+      allowSubstitutes = false;
+    };
+
+  modulePaths =
+    let
+      dependencies = fromJSON (readFile lockFile);
+      modules = mapAttrs mkModule dependencies;
+    in
+    filter lib.isDerivation (attrValues modules);
+
+  mavenRepo = symlinkJoin {
+    name = "gradle-maven-repo";
+    paths = modulePaths;
+    passthru.gradleInitScript = substitute {
+      src = ./init.gradle;
+      substitutions = [
+        "--replace"
+        "@mavenRepo@"
+        "${mavenRepo}"
+      ];
+    };
+  };
+in
+mavenRepo