Add dependencies for gradle plugin (for custom rules)

Following the feature request https://github.com/arturbosch/detekt/issues/795,
this commit implements a way to configure Detekt plugins using Gradle plugin.

README.md

@@ -37,6 +37,7 @@ It operates on the abstract syntax tree provided by the Kotlin compiler.
     3. [in android projects](#gradleandroid)
     4. [plugin tasks](#tasks)
     5. [detekt-closure](#closure)
+    6. [custom rules](#gradleCustomRules)
 3. [Standalone gradle task](#gradle)
 4. [Standalone maven task](#maventask)
 5. [Rule sets](#rulesets)
@@ -298,6 +299,26 @@ detekt {
 
 For more information on using idea as a headless formatting/inspection tool see [here](https://www.jetbrains.com/help/idea/working-with-intellij-idea-features-from-command-line.html).
 
+##### <a name="gradleCustomRules">Using custom rules with Gradle plugin</a>
+
+When your _detekt_ custom rules are located in a module of your Gradle project (e.g. `:detekt-extensions`), you can
+enable them with the following syntax:
+
+```groovy
+dependencies {
+    detekt project(':detekt-extensions')
+}
+
+detekt {
+    profile("main") {
+        input = "$projectDir/src/main/kotlin"
+    }
+}
+```
+
+More generally, you can use dependencies on `detekt` configuration; these dependencies will be resolved, built if
+needed, and added to _detekt_ classpath.
+
 #### <a name="gradle">Using _detekt_ in custom gradle projects</a>
 
 1. Add following lines to your build.gradle file.
@@ -597,7 +618,7 @@ If you contributed to detekt but your name is not in the list, please feel free
 - [Svyatoslav Chatchenko](https://github.com/MyDogTom) - Active on Issues, NamingConventions and UnusedImport fixes
 - [Sean Flanigan](https://github.com/seanf) - Config from classpath resource
 - [Sebastian Schuberth](https://github.com/sschuberth) - Active on Issues, Windows support
-- [Olivier Lemasle](https://github.com/olivierlemasle) - NP-Bugfix
+- [Olivier Lemasle](https://github.com/olivierlemasle) - NP-Bugfix, fix TooGenericExceptionCaught, Gradle plugin improvement
 - [Marc Prengemann](https://github.com/winterDroid) - Support for custom output formats, prototyped Rule-Context-Issue separation
 - [Sebastiano Poggi](https://github.com/rock3r) - Enhanced milestone report script, Magic number fixes
 - [Ilya Tretyakov](https://github.com/jvilya) - Sonar runs should not auto correct formatting.

detekt-gradle-plugin/src/main/kotlin/io/gitlab/arturbosch/detekt/DetektCheckTask.kt

@@ -4,7 +4,7 @@ import io.gitlab.arturbosch.detekt.extensions.DetektExtension
 import io.gitlab.arturbosch.detekt.extensions.INPUT_PARAMETER
 import io.gitlab.arturbosch.detekt.extensions.OUTPUT_PARAMETER
 import org.gradle.api.DefaultTask
-import org.gradle.api.internal.artifacts.dependencies.DefaultExternalModuleDependency
+import org.gradle.api.file.FileCollection
 import org.gradle.api.tasks.InputDirectory
 import org.gradle.api.tasks.OutputDirectory
 import org.gradle.api.tasks.TaskAction
@@ -13,6 +13,7 @@ import java.io.File
 /**
  * @author Artur Bosch
  * @author Marvin Ramin
+ * @author Olivier Lemasle
  */
 open class DetektCheckTask : DefaultTask() {
 
@@ -22,6 +23,8 @@ open class DetektCheckTask : DefaultTask() {
 	@OutputDirectory
 	val output: File?
 
+	private val classpath: FileCollection
+
 	init {
 		description = "Analyze your kotlin code with detekt."
 		group = "verification"
@@ -33,19 +36,18 @@ open class DetektCheckTask : DefaultTask() {
 
 		val outputIndex = arguments.indexOf(OUTPUT_PARAMETER)
 		output = File(arguments[outputIndex + 1])
+
+		classpath = detektExtension.resolveClasspath(project)
+		dependsOn(classpath)
 	}
 
 	@TaskAction
 	fun check() {
 		val detektExtension = project.extensions.getByName("detekt") as DetektExtension
 
-		val configuration = project.buildscript.configurations.maybeCreate("detektCheck")
-		project.buildscript.dependencies.add(configuration.name, DefaultExternalModuleDependency(
-				"io.gitlab.arturbosch.detekt", "detekt-cli", detektExtension.version))
-
 		project.javaexec {
 			it.main = "io.gitlab.arturbosch.detekt.cli.Main"
-			it.classpath = configuration
+			it.classpath = classpath
 			it.args(detektExtension.resolveArguments(project))
 		}
 	}

detekt-gradle-plugin/src/main/kotlin/io/gitlab/arturbosch/detekt/DetektCreateBaselineTask.kt

@@ -2,17 +2,24 @@ package io.gitlab.arturbosch.detekt
 
 import io.gitlab.arturbosch.detekt.extensions.DetektExtension
 import org.gradle.api.DefaultTask
-import org.gradle.api.internal.artifacts.dependencies.DefaultExternalModuleDependency
+import org.gradle.api.file.FileCollection
 import org.gradle.api.tasks.TaskAction
 
 /**
  * @author Artur Bosch
+ * @author Olivier Lemasle
  */
 open class DetektCreateBaselineTask : DefaultTask() {
 
+	private val classpath: FileCollection
+
 	init {
 		description = "Creates a detekt baseline on the given --baseline path."
 		group = "verification"
+
+		val detektExtension = project.extensions.getByName("detekt") as DetektExtension
+		classpath = detektExtension.resolveClasspath(project)
+		dependsOn(classpath)
 	}
 
 	private val createBaseline = "--create-baseline"
@@ -21,13 +28,9 @@ open class DetektCreateBaselineTask : DefaultTask() {
 	fun baseline() {
 		val detektExtension = project.extensions.getByName("detekt") as DetektExtension
 
-		val configuration = project.buildscript.configurations.maybeCreate("detektBaseline")
-		project.buildscript.dependencies.add(configuration.name, DefaultExternalModuleDependency(
-				"io.gitlab.arturbosch.detekt", "detekt-cli", detektExtension.version))
-
 		project.javaexec {
 			it.main = "io.gitlab.arturbosch.detekt.cli.Main"
-			it.classpath = configuration
+			it.classpath = classpath
 			it.args(detektExtension.resolveArguments(project).plus(createBaseline))
 		}
 	}

detekt-gradle-plugin/src/main/kotlin/io/gitlab/arturbosch/detekt/DetektGenerateConfigTask.kt

@@ -2,30 +2,31 @@ package io.gitlab.arturbosch.detekt
 
 import io.gitlab.arturbosch.detekt.extensions.DetektExtension
 import org.gradle.api.DefaultTask
-import org.gradle.api.internal.artifacts.dependencies.DefaultExternalModuleDependency
+import org.gradle.api.file.FileCollection
 import org.gradle.api.tasks.TaskAction
 
 /**
  * @author Artur Bosch
+ * @author Olivier Lemasle
  */
 open class DetektGenerateConfigTask : DefaultTask() {
 
+	private val classpath: FileCollection
+
 	init {
 		description = "Generate a detekt configuration file inside your project."
 		group = "verification"
+
+		val detektExtension = project.extensions.getByName("detekt") as DetektExtension
+		classpath = detektExtension.resolveClasspath(project)
+		dependsOn(classpath)
 	}
 
 	@TaskAction
 	fun generateConfig() {
-		val detektExtension = project.extensions.getByName("detekt") as DetektExtension
-
-		val configuration = project.buildscript.configurations.maybeCreate("detektConfig")
-		project.buildscript.dependencies.add(configuration.name, DefaultExternalModuleDependency(
-				"io.gitlab.arturbosch.detekt", "detekt-cli", detektExtension.version))
-
 		project.javaexec {
 			it.main = "io.gitlab.arturbosch.detekt.cli.Main"
-			it.classpath = configuration
+			it.classpath = classpath
 			it.args("--input", project.projectDir.absolutePath, "--generate-config")
 		}
 	}

detekt-gradle-plugin/src/main/kotlin/io/gitlab/arturbosch/detekt/DetektPlugin.kt

@@ -9,6 +9,8 @@ import org.gradle.api.Project
 class DetektPlugin : Plugin<Project> {
 
 	override fun apply(project: Project) {
+		project.configurations.create("detekt")
+
 		val profilesContainer = project.container(ProfileExtension::class.java)
 		project.extensions.add(PROFILES_EXTENSION_NAME, profilesContainer)
 		profilesContainer.all { ProfileStorage.add(it) }

detekt-gradle-plugin/src/main/kotlin/io/gitlab/arturbosch/detekt/extensions/DetektExtension.kt

@@ -2,10 +2,13 @@ package io.gitlab.arturbosch.detekt.extensions
 
 import org.gradle.api.Action
 import org.gradle.api.Project
+import org.gradle.api.file.FileCollection
+import org.gradle.api.internal.artifacts.dependencies.DefaultExternalModuleDependency
 
 /**
  * @author Artur Bosch
  * @author Said Tahsin Dane
+ * @author Olivier Lemasle
  */
 open class DetektExtension(open var version: String = SUPPORTED_DETEKT_VERSION,
 						   open var debug: Boolean = DEFAULT_DEBUG_VALUE,
@@ -34,6 +37,17 @@ open class DetektExtension(open var version: String = SUPPORTED_DETEKT_VERSION,
 		}
 	}
 
+	fun resolveClasspath(project: Project): FileCollection = project
+		.configurations
+		.getByName("detekt")
+		.withDependencies {
+			it.add(
+				DefaultExternalModuleDependency(
+					"io.gitlab.arturbosch.detekt", "detekt-cli", version
+				)
+			)
+		}
+
 	fun resolveArguments(project: Project): List<String> {
 		return with(extractArguments()) {
 			if (!contains(INPUT_PARAMETER)) {

detekt-gradle-plugin/src/test/kotlin/io/gitlab/arturbosch/detekt/FunctionalTest.kt

@@ -0,0 +1,133 @@
+package io.gitlab.arturbosch.detekt
+
+import org.assertj.core.api.Assertions.assertThat
+import org.jetbrains.spek.api.Spek
+import org.jetbrains.spek.api.dsl.describe
+import org.jetbrains.spek.api.dsl.it
+import org.gradle.testkit.runner.GradleRunner
+import org.gradle.testkit.runner.TaskOutcome
+import java.io.File
+
+/**
+ * @author Olivier Lemasle
+ */
+internal class FunctionalTest : Spek({
+
+	describe("The Detekt Gradle plugin") {
+
+		it("uses built-in rules") {
+			val rootDir = createTempDir(prefix = "withoutCustomRules")
+			writeFiles(rootDir)
+
+			// Using a custom "project-cache-dir" to avoid a Gradle error on Windows
+			val result = GradleRunner.create()
+				.withProjectDir(rootDir)
+				.withArguments("--project-cache-dir", createTempDir(prefix = "cache").absolutePath, "detektCheck")
+				.withPluginClasspath()
+				.build()
+
+			assertThat(result.output).contains("number of classes: 1")
+			assertThat(result.output).contains("Ruleset: comments")
+			assertThat(result.task(":detektCheck")?.outcome).isEqualTo(TaskOutcome.SUCCESS)
+
+			// Asserts that the "custom" module is not built, and that custom ruleset is not enabled
+			assertThat(result.output).doesNotContain("Ruleset: test-custom")
+			assertThat(File(rootDir, "custom/build")).doesNotExist()
+		}
+
+		it("can use custom rules from a project's module") {
+			val rootDir = createTempDir(prefix = "withCustomRules")
+			writeFiles(rootDir)
+
+			File(rootDir, "build.gradle").appendText(
+				"""
+				|dependencies {
+				|   detekt project(':custom')
+				|}
+				""".trimMargin()
+			)
+
+			val result = GradleRunner.create()
+				.withProjectDir(rootDir)
+				.withArguments("--project-cache-dir", createTempDir(prefix = "cache").absolutePath, "detektCheck")
+				.withPluginClasspath()
+				.build()
+
+			assertThat(result.output).contains("number of classes: 1")
+			assertThat(result.output).contains("Ruleset: comments")
+			assertThat(result.task(":detektCheck")?.outcome).isEqualTo(TaskOutcome.SUCCESS)
+
+			// Asserts that the "custom" module is built, and that custom ruleset is enabled
+			assertThat(result.output).contains("Ruleset: test-custom")
+			assertThat(File(rootDir, "custom/build")).exists()
+		}
+	}
+})
+
+// build.gradle
+private val buildFileContent = """
+	|plugins {
+	|   id 'io.gitlab.arturbosch.detekt'
+	|}
+	|repositories {
+	|   jcenter()
+	|}
+	|detekt {
+	|   profile('main') {
+	|      input = "${"$"}projectDir/src/main/kotlin"
+	|   }
+	|}
+	|
+	""".trimMargin()
+
+// settings.gradle
+private const val settingsFileContent = """include ":custom""""
+
+// src/main/kotlin/MyClass.kt
+private val ktFileContent = """
+	|class MyClass
+	|
+	""".trimMargin()
+
+// custom/build.gradle
+private val customBuildFileContent = """
+	|plugins {
+	|   id "org.jetbrains.kotlin.jvm" version "1.2.31"
+	|}
+	|repositories {
+	|   jcenter()
+	|}
+	|dependencies {
+	|   implementation "io.gitlab.arturbosch.detekt:detekt-api:1.0.0.RC6-4"
+	|}
+	""".trimMargin()
+
+// custom/src/main/kotlin/RulesProvider.kt
+private val customRulesProviderContent = """
+	|import io.gitlab.arturbosch.detekt.api.Config
+	|import io.gitlab.arturbosch.detekt.api.RuleSet
+	|import io.gitlab.arturbosch.detekt.api.RuleSetProvider
+	|
+	|class RulesProvider : RuleSetProvider {
+	|   override val ruleSetId: String = "test-custom"
+	|   override fun instance(config: Config) = RuleSet(ruleSetId, listOf())
+	|}
+	|
+	""".trimMargin()
+
+// custom/src/main/resources/META-INF/services/io.gitlab.arturbosch.detekt.api.RuleSetProvider
+private const val ruleSetProviderSpiContent = "RulesProvider"
+
+private fun writeFiles(root: File) {
+	File(root, "build.gradle").writeText(buildFileContent)
+	File(root, "settings.gradle").writeText(settingsFileContent)
+	File(root, "src/main/kotlin").mkdirs()
+	File(root, "src/main/kotlin/MyClass.kt").writeText(ktFileContent)
+	File(root, "custom").mkdirs()
+	File(root, "custom/build.gradle").writeText(customBuildFileContent)
+	File(root, "custom/src/main/kotlin").mkdirs()
+	File(root, "custom/src/main/kotlin/RulesProvider.kt").writeText(customRulesProviderContent)
+	File(root, "custom/src/main/resources/META-INF/services").mkdirs()
+	File(root, "custom/src/main/resources/META-INF/services/io.gitlab.arturbosch.detekt.api.RuleSetProvider")
+		.writeText(ruleSetProviderSpiContent)
+}