Allow overriding dependencies in gradle.nix

gradle.nix

@@ -32,16 +32,20 @@
 , writeTextDir
 }:
 
+let defaultGradle = gradle; in
+
 {
   # Path to the lockfile generated by gradle2nix (e.g. gradle.lock).
-  lockFile
+  lockFile ? null
 , pname ? "project"
 , version ? null
 , enableParallelBuilding ? true
+# The Gradle package to use. Default is 'pkgs.gradle'.
+, gradle ? defaultGradle
 # Arguments to Gradle used to build the project in buildPhase.
 , gradleFlags ? [ "build" ]
-# Enable debugging for the Gradle build; this will cause Gradle to run a debug server
-# and wait for a JVM debugging client to attach.
+# 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 ? ""
@@ -65,52 +69,79 @@
 #     };
 #   }
 , fetchers ? { }
+# Overlays for dependencies in the offline Maven repository.
+#
+# Acceps an attrset of dependencies (usually parsed from 'lockFile'), and produces an attrset
+# containing dependencies to merge into the final set.
+#
+# The attrset is of the form:
+#
+#   {
+#      "${group}:${module}:${version}" = <derivation>;
+#      # ...
+#   }
+#
+# A dependency derivation unpacks multiple source files into a single Maven-style directory named
+# "${out}/${groupPath}/${module}/${version}/", where 'groupPath' is the dependency group ID with dot
+# characters ('.') replaced by the path separator ('/').
+#
+# Examples:
+#
+# 1. Add or replace a dependency with a single JAR file:
+#
+#    (_: {
+#      "com.squareup.okio:okio:3.9.0" = fetchurl {
+#        url = "https://repo.maven.apache.org/maven2/com/squareup/okio/okio/3.9.0/okio-3.9.0.jar";
+#        hash = "...";
+#        downloadToTemmp = true;
+#        postFetch = "install -Dt $out/com/squareup/okio/okio/3.9.0/ $downloadedFile"
+#      };
+#    })
+#
+# 2. Remove a dependency entirely:
+#
+#    # This works because the result is filtered for values that are derivations.
+#    (_: {
+#      "org.apache.log4j:core:2.23.1" = null;
+#    })
+, overlays ? []
 , ... } @ args:
 
 let
   inherit (builtins)
-    attrValues concatStringsSep elemAt filter fromJSON getAttr hasAttr head length match
-    removeAttrs replaceStrings sort;
+    attrValues concatStringsSep elemAt filter fromJSON getAttr head length mapAttrs removeAttrs
+    replaceStrings;
 
   inherit (lib)
-    assertMsg concatMapStringsSep findFirst foldl' groupBy' hasSuffix hasPrefix last mapAttrs
-    mapAttrsToList optionalAttrs optionalString readFile removeSuffix unique versionAtLeast
-    versionOlder;
+    mapAttrsToList optionalString readFile versionAtLeast versionOlder;
 
   inherit (lib.strings) sanitizeDerivationName;
 
-  lockedDeps = fromJSON (readFile lockFile);
-
   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;
-      versionParts = parseVersion version;
+      uniqueVersion = parseVersion version;
     };
 
-  parseVersion = version:
-    let
-      parts = builtins.split ":" version;
-      base = elemAt parts 0;
-    in
-      {
-        inherit base;
-        exact = base;
-      }
-      // optionalAttrs (length parts >= 2) (
-        let
-          snapshot = elemAt parts 2;
-          exact = replaceStrings [ "-SNAPSHOT" ] [ "-${snapshot}" ] base;
-          parts = builtins.split "-" timestamp;
-          timestamp = findFirst (match "[0-9]{8}\.[0-9]{6}") parts;
-          buildNumber = let lastPart = last parts; in if match "[0-9]+" lastPart then lastPart else null;
-        in
-          { inherit snapshot exact timestamp buildNumber; }
-      );
-
   fetchers' = {
     http = fetchurl;
     https = fetchurl;
@@ -133,7 +164,7 @@ let
     in
       stdenv.mkDerivation {
         pname = sanitizeDerivationName "${coords.group}-${coords.module}";
-        version = coords.versionParts.exact;
+        version = coords.uniqueVersion;
 
         srcs = mapAttrsToList fetch artifacts;
 
@@ -157,9 +188,30 @@ let
         allowSubstitutes = false;
       };
 
+  # Intermediate dependency spec.
+  #
+  # We want to allow overriding dependencies via the 'dependencies' function,
+  # so we pass an intermediate set that maps each Maven coordinate to the
+  # derivation created with 'mkModule'. This allows users extra flexibility
+  # to do things like patching native libraries with patchelf or replacing
+  # artifacts entirely.
+  lockedDependencies = final: if lockFile == null then {} else
+    let
+      lockedDependencySpecs = fromJSON (readFile lockFile);
+    in mapAttrs mkModule lockedDependencySpecs;
+
+
+  finalDependencies =
+    let
+      composedExtension = lib.composeManyExtensions overlays;
+      extended = lib.extends composedExtension lockedDependencies;
+      fixed = lib.fix extended;
+    in
+      filter lib.isDerivation (attrValues fixed);
+
   offlineRepo = symlinkJoin {
     name = if version != null then "${pname}-${version}-gradle-repo" else "${pname}-gradle-repo";
-    paths = mapAttrsToList mkModule lockedDeps;
+    paths = finalDependencies;
   };
 
   initScript =
@@ -227,64 +279,53 @@ let
         ${extraInit}
       '';
 
-  buildProject = flags: ''
-    gradle --offline --no-daemon --no-build-cache \
-      --info --full-stacktrace --warning-mode=all \
-      --no-configuration-cache \
-      -Dmaven.repo.local=${offlineRepo} \
-      ${optionalString enableParallelBuilding "--parallel"} \
-      ${optionalString enableDebug "-Dorg.gradle.debug=true"} \
-      ${optionalString (buildJdk != null) "-Dorg.gradle.java.home=${buildJdk.home}"} \
-      --init-script ${initScript} \
-      ${concatStringsSep " " flags}
-  '';
 
-in stdenv.mkDerivation ({
+  buildGradle = stdenv.mkDerivation (finalAttrs: {
 
-  dontStrip = true;
+    inherit buildJdk enableParallelBuilding enableDebug gradle gradleFlags pname version;
 
-  nativeBuildInputs = (args.nativeBuildInputs or []) ++ [ gradle ];
+    dontStrip = true;
 
-  buildPhase = args.buildPhase or ''
-    runHook preBuild
+    nativeBuildInputs = [ finalAttrs.gradle ]
+                        ++ lib.optional (finalAttrs.buildJdk != null) finalAttrs.buildJdk;
 
-    (
-    set -eux
+    buildPhase = ''
+      runHook preBuild
 
-    ${optionalString (versionOlder gradle.version "8.0") ''
-      # Work around https://github.com/gradle/gradle/issues/1055
-      TMPHOME="$(mktemp -d)"
-      mkdir -p "$TMPHOME/init.d"
-      export GRADLE_USER_HOME="$TMPHOME"
-      cp ${initScript} $TMPHOME/
-    ''}
+      (
+      set -eux
 
-    gradle --offline --no-daemon --no-build-cache \
-      --info --full-stacktrace --warning-mode=all \
-      --no-configuration-cache --console=plain \
-      -Dmaven.repo.local=${offlineRepo} \
-      ${optionalString enableParallelBuilding "--parallel"} \
-      ${optionalString enableDebug "-Dorg.gradle.debug=true"} \
-      ${optionalString (buildJdk != null) "-Dorg.gradle.java.home=${buildJdk.home}"} \
-      --init-script ${initScript} \
-      ${concatStringsSep " " gradleFlags}
-    )
+      ${optionalString (versionOlder finalAttrs.gradle.version "8.0") ''
+        # Work around https://github.com/gradle/gradle/issues/1055
+        TMPHOME="$(mktemp -d)"
+        mkdir -p "$TMPHOME/init.d"
+        export GRADLE_USER_HOME="$TMPHOME"
+        cp ${initScript} $TMPHOME/
+      ''}
 
-    runHook postBuild
-  '';
+      gradle --offline --no-daemon --no-build-cache \
+        --info --full-stacktrace --warning-mode=all \
+        --no-configuration-cache --console=plain \
+        -Dmaven.repo.local=${offlineRepo} \
+        ${optionalString finalAttrs.enableParallelBuilding "--parallel"} \
+        ${optionalString finalAttrs.enableDebug "-Dorg.gradle.debug=true"} \
+        ${optionalString (finalAttrs.buildJdk != null) "-Dorg.gradle.java.home=${finalAttrs.buildJdk.home}"} \
+        --init-script ${initScript} \
+        ${concatStringsSep " " finalAttrs.gradleFlags}
+      )
 
-  passthru = (args.passthru or {}) // {
-    inherit offlineRepo;
-  };
+      runHook postBuild
+    '';
 
-} // (removeAttrs args [
-  "nativeBuildInputs"
-  "passthru"
-  "lockFile"
-  "gradleFlags"
-  "gradle"
-  "enableDebug"
-  "extraInit"
-  "buildJdk"
-  "fetchers"
-]))
+    passthru = {
+      inherit offlineRepo;
+    };
+  } // removeAttrs args [
+    "lockFile"
+    "extraInit"
+    "fetchers"
+    "overlays"
+  ]);
+
+in
+buildGradle