Allow overriding the Gradle installation

README.org

@@ -95,14 +95,21 @@ nix run github:tadfisher/gradle2nix -- --help
 #+begin_example
 Usage: gradle2nix [<options>] [<args>]...
 
+Gradle installation:
+
+  Where to find Gradle. By default, use the project's wrapper.
+
+  --gradle-dist=<uri>       Gradle distribution URI
+  --gradle-home=<dir>       Gradle home path (e.g. `nix eval nixpkgs#gradle.outPath`/lib/gradle)
+  --gradle-wrapper=<value>  Gradle wrapper version
+
 Options:
-  -t, --tasks=<tasks>             Gradle tasks to run
-  -p, --project=<project-dir>     Path to the project root (default: Current directory)
+  -t, --task=<task>              Gradle tasks to run
+  -p, --project=<path>           Path to the project root (default: Current directory)
   -o, --out-dir=<dir>            Path to write generated files (default: <project>)
   -l, --lock-file=<filename>     Name of the generated lock file (default: gradle.lock)
   -n, --nix-file=<filename>      Name of the generated Nix file (default: gradle.nix)
-  -g, --gradle-version=<version>  Use a specific Gradle version
-  -j, --gradle-jdk=<dir>          JDK home directory to use for launching Gradle (default: JAVA_HOME)
+  -j, --gradle-jdk=<dir>         JDK home to use for launching Gradle (e.g. nix eval nixpkgs#openjdk.home)
   --log=(debug|info|warn|error)  Print messages with this priority or higher (default: error)
   --dump-events                  Dump Gradle event logs to the output directory
   --stacktrace                   Print a stack trace on error
@@ -137,16 +144,21 @@ gradle2nix -t :app:installDist
 /Note:/ This may be *required* if the build resolves configurations
 at execution time.
 
-*** Specifying the Gradle version
+*** Specifying the Gradle installation
 
-By default, if the project has configured the Gradle wrapper, that
-version will be detected and pinned; otherwise, the version of Gradle
-installed on your system will be pinned. You can override this with
-the =--gradle-version= argument, which also avoids the need to have
-Gradle installed.
+By default, if the project has configured the Gradle wrapper, it will
+be used; otherwise, the version of Gradle used to build gradle2nix
+will be used. You can override this to use any of the following:
 
 #+begin_example
-gradle2nix -g 6.1
+# Gradle distribution URL:
+gradle2nix --gradle-dist='https://services.gradle.org/distributions/gradle-8.7-bin.zip'
+
+# Path to a local Gradle installation:
+gradle2nix --gradle-home=`nix eval nixpkgs#gradle.outPath`/lib/gradle
+
+# A specific wrapper version:
+gradle2nix --gradle-wrapper=8.7
 #+end_example
 
 ** Contributing

app/src/main/kotlin/org/nixos/gradle2nix/GradleRunner.kt

@@ -16,8 +16,11 @@ import org.nixos.gradle2nix.model.RESOLVE_ALL_TASK
 fun connect(config: Config, projectDir: File = config.projectDir): ProjectConnection =
     GradleConnector.newConnector()
         .apply {
-            if (config.gradleVersion != null) {
-                useGradleVersion(config.gradleVersion)
+            when (val source = config.gradleSource) {
+                is GradleSource.Distribution -> useDistribution(source.uri)
+                is GradleSource.Path -> useInstallation(source.path)
+                GradleSource.Project -> useBuildDistribution()
+                is GradleSource.Wrapper -> useGradleVersion(source.version)
             }
         }
         .forProjectDirectory(projectDir)

app/src/main/kotlin/org/nixos/gradle2nix/Main.kt

@@ -5,26 +5,33 @@ import com.github.ajalt.clikt.core.context
 import com.github.ajalt.clikt.output.MordantHelpFormatter
 import com.github.ajalt.clikt.parameters.arguments.argument
 import com.github.ajalt.clikt.parameters.arguments.multiple
+import com.github.ajalt.clikt.parameters.groups.default
+import com.github.ajalt.clikt.parameters.groups.mutuallyExclusiveOptions
+import com.github.ajalt.clikt.parameters.groups.single
+import com.github.ajalt.clikt.parameters.options.convert
 import com.github.ajalt.clikt.parameters.options.default
 import com.github.ajalt.clikt.parameters.options.defaultLazy
 import com.github.ajalt.clikt.parameters.options.flag
 import com.github.ajalt.clikt.parameters.options.multiple
 import com.github.ajalt.clikt.parameters.options.option
+import com.github.ajalt.clikt.parameters.options.optionalValue
 import com.github.ajalt.clikt.parameters.options.validate
 import com.github.ajalt.clikt.parameters.types.enum
 import com.github.ajalt.clikt.parameters.types.file
 import java.io.File
+import java.net.URI
 import kotlinx.coroutines.runBlocking
 import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.encodeToStream
+import org.gradle.internal.service.scopes.Scopes.Gradle
 import org.gradle.tooling.model.gradle.GradleBuild
 import org.nixos.gradle2nix.model.DependencySet
 
 data class Config(
     val appHome: File,
     val gradleHome: File,
-    val gradleVersion: String?,
+    val gradleSource: GradleSource,
     val gradleJdk: File?,
     val gradleArgs: List<String>,
     val outDir: File,
@@ -41,6 +48,13 @@ val JsonFormat = Json {
     prettyPrintIndent = "  "
 }
 
+sealed interface GradleSource {
+    data class Distribution(val uri: URI) : GradleSource
+    data class Path(val path: File) : GradleSource
+    data object Project : GradleSource
+    data class Wrapper(val version: String) : GradleSource
+}
+
 enum class LogLevel {
     debug,
     info,
@@ -49,7 +63,7 @@ enum class LogLevel {
 }
 
 class Gradle2Nix : CliktCommand(
-    name = "gradle2nix"
+    name = "gradle2nix",
 ) {
     private val tasks: List<String> by option(
         "--task", "-t",
@@ -88,16 +102,29 @@ class Gradle2Nix : CliktCommand(
         help = "Name of the generated Nix file"
     ).default("gradle.nix")
 
-    private val gradleVersion: String? by option(
-        "--gradle-version", "-g",
-        metavar = "VERSION",
-        help = "Use a specific Gradle version"
-    )
+    private val gradleSource: GradleSource by mutuallyExclusiveOptions(
+        option(
+            "--gradle-dist",
+            metavar = "URI",
+            help = "Gradle distribution URI"
+        ).convert { GradleSource.Distribution(URI(it)) },
+        option(
+            "--gradle-home",
+            metavar = "DIR",
+            help = "Gradle home path (e.g. \\`nix eval nixpkgs#gradle.outPath\\`/lib/gradle)"
+        ).file(mustExist = true, canBeFile = false).convert { GradleSource.Path(it) },
+        option(
+            "--gradle-wrapper",
+            help = "Gradle wrapper version"
+        ).convert { GradleSource.Wrapper(it) },
+        name = "Gradle installation",
+        help = "Where to find Gradle. By default, use the project's wrapper."
+    ).single().default(GradleSource.Project)
 
     private val gradleJdk: File? by option(
         "--gradle-jdk", "-j",
         metavar = "DIR",
-        help = "JDK home directory to use for launching Gradle (default: ${System.getProperty("java.home")})"
+        help = "JDK home to use for launching Gradle (e.g. `nix eval nixpkgs#openjdk.home`)",
     ).file(canBeFile = false, canBeDir = true)
 
     private val logLevel: LogLevel by option(
@@ -138,7 +165,7 @@ class Gradle2Nix : CliktCommand(
         val config = Config(
             appHome,
             gradleHome,
-            gradleVersion,
+            gradleSource,
             gradleJdk,
             gradleArgs,
             outDir ?: projectDir,