Added an API to allow creating independent tasks in the gradle plugin.

CONTRIBUTING.md

@@ -115,6 +115,57 @@ The gist of it is that you will have to:
 
 If you get something running, we'd love to host your plugin within this repo as a peer to `plugin-gradle` and `plugin-maven`.
 
+## Integration testing
+
+### Locally
+
+First, run `./gradlew publishToMavenLocal` in your local checkout of Spotless.  Now, in any other project on your machine, you can use the following snippet in your `settings.gradle` (for Gradle 6.0+).
+
+```
+pluginManagement {
+  repositories {
+    mavenLocal {
+      content {
+        includeGroup 'com.diffplug.spotless'
+      }
+    }
+    gradlePluginPortal()
+  }
+  resolutionStrategy {
+    eachPlugin {
+      if (requested.id.id == 'com.diffplug.gradle.spotless') {
+        useModule('com.diffplug.spotless:spotless-plugin-gradle:{latest-SNAPSHOT}')
+      }
+    }
+  }
+}
+```
+
+### Any commit in a public GitHub repo (this one, or any fork)
+
+In Gradle 6.0+, you can use the following snippet in your `settings.gradle`.  TODO: broken until [jitpack/jitpack.io#4112](https://github.com/jitpack/jitpack.io/issues/4112) is resolved.
+
+```gradle
+pluginManagement {
+  repositories {
+    maven {
+      url 'https://jitpack.io'
+      content {
+        includeGroup 'com.github.{{user-or-org}}.spotless'
+      }
+    }
+    gradlePluginPortal()
+  }
+  resolutionStrategy {
+    eachPlugin {
+      if (requested.id.id == 'com.diffplug.gradle.spotless') {
+        useModule('com.github.{{user-or-org}}.spotless:spotless-plugin-gradle:SHA_OF_COMMIT_YOU_WANT')
+      }
+    }
+  }
+}
+```
+
 ## License
 
 By contributing your code, you agree to license your contribution under the terms of the APLv2: https://github.com/diffplug/spotless/blob/master/LICENSE.txt

lib/src/main/java/com/diffplug/spotless/markdown/LibMarkdownPreconditions.java

@@ -25,8 +25,9 @@ private LibMarkdownPreconditions() {}
 	static <K, V> Map<K, V> requireKeysAndValuesNonNull(Map<K, V> map) {
 		Objects.requireNonNull(map);
 		map.forEach((key, value) -> {
-			Objects.requireNonNull(key);
-			Objects.requireNonNull(value);
+			String errorMessage = key + "=" + value;
+			Objects.requireNonNull(key, errorMessage);
+			Objects.requireNonNull(value, errorMessage);
 		});
 		return map;
 	}

plugin-gradle/CHANGES.md

@@ -2,6 +2,8 @@
 
 ### Version 3.27.0-SNAPSHOT - TBD ([javadoc](https://diffplug.github.io/spotless/javadoc/snapshot/), [snapshot](https://oss.sonatype.org/content/repositories/snapshots/com/diffplug/spotless/spotless-plugin-gradle/))
 
+* Added method `FormatExtension.createIndependentTask(String taskName)` which allows creating a Spotless task outside of the `check`/`apply` lifecycle.  See [javadoc](https://github.com/diffplug/spotless/blob/91ed7203994e52058ea6c2e0f88d023ed290e433/plugin-gradle/src/main/java/com/diffplug/gradle/spotless/FormatExtension.java#L613-L639) for details.
+
 ### Version 3.26.1 - November 27th 2019 ([javadoc](https://diffplug.github.io/spotless/javadoc/spotless-plugin-gradle/3.26.1/), [jcenter](https://bintray.com/diffplug/opensource/spotless-plugin-gradle/3.26.1))
 
 * Revert the change in console display of errors from 3.26.0 ([#485](https://github.com/diffplug/spotless/pull/485)) because [of these problems](https://github.com/diffplug/spotless/pull/485#issuecomment-552925932).

plugin-gradle/README.md

@@ -611,6 +611,8 @@ If you use `custom` or `customLazy`, you might want to take a look at [this java
 
 See [`JavaExtension.java`](src/main/java/com/diffplug/gradle/spotless/JavaExtension.java) if you'd like to see how a language-specific set of custom rules is implemented.  We'd love PR's which add support for other languages.
 
+If you'd like to create a one-off Spotless task outside of the `check`/`apply` framework, see [`FormatExtension.createIndependentTask`](https://github.com/diffplug/spotless/blob/91ed7203994e52058ea6c2e0f88d023ed290e433/plugin-gradle/src/main/java/com/diffplug/gradle/spotless/FormatExtension.java#L613-L639).
+
 <a name="invisible"></a>
 
 ## Line endings and encodings (invisible stuff)

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/FormatExtension.java

@@ -27,7 +27,9 @@
 
 import org.gradle.api.GradleException;
 import org.gradle.api.Project;
+import org.gradle.api.Task;
 import org.gradle.api.file.FileCollection;
+import org.gradle.api.plugins.BasePlugin;
 import org.gradle.api.tasks.util.PatternFilterable;
 
 import com.diffplug.spotless.FormatExceptionPolicyStrict;
@@ -607,4 +609,32 @@ protected void setupTask(SpotlessTask task) {
 	protected Project getProject() {
 		return root.project;
 	}
+
+	/**
+	 * Creates an independent {@link SpotlessTask} for (very) unusual circumstances.
+	 *
+	 * Most users will not want this method.  In the rare case that you want to create
+	 * a SpotlessTask which is independent of the normal Spotless machinery, this will
+	 * let you do that.
+	 *
+	 * The returned task will have no dependencies on any other task.
+	 * You need to call {@link SpotlessTask#setApply()} and/or {@link SpotlessTask#setCheck()}
+	 * on the return value, otherwise you will get a runtime error when the task tries to run.
+	 *
+	 * NOTE: does not respect the rarely-used [`spotlessFiles` property](https://github.com/diffplug/spotless/blob/b7f8c551a97dcb92cc4b0ee665448da5013b30a3/plugin-gradle/README.md#can-i-apply-spotless-to-specific-files).
+	 */
+	public SpotlessTask createIndependentTask(String taskName) {
+		// create and setup the task
+		SpotlessTask spotlessTask = root.project.getTasks().create(taskName, SpotlessTask.class);
+		setupTask(spotlessTask);
+
+		// enforce the clean ordering
+		Task clean = root.project.getTasks().getByName(BasePlugin.CLEAN_TASK_NAME);
+		spotlessTask.mustRunAfter(clean);
+
+		// ignore the filePatterns
+		spotlessTask.setFilePatterns("");
+
+		return spotlessTask;
+	}
 }

plugin-gradle/src/test/java/com/diffplug/gradle/spotless/IndependentTaskTest.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2016 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.gradle.spotless;
+
+import java.io.IOException;
+
+import org.junit.Test;
+
+public class IndependentTaskTest extends GradleIntegrationTest {
+	@Test
+	public void independent() throws IOException {
+		setFile("build.gradle").toLines(
+				"buildscript { repositories { mavenCentral() } }",
+				"plugins {",
+				"    id 'com.diffplug.gradle.spotless'",
+				"}",
+				"",
+				"import com.diffplug.gradle.spotless.JavaExtension",
+				"",
+				"def underTest = new JavaExtension(spotless)",
+				"underTest.target file('test.java')",
+				"underTest.googleJavaFormat('1.2')",
+				"",
+				"def independent = underTest.createIndependentTask('independent')",
+				"independent.setApply()");
+		setFile("test.java").toResource("java/googlejavaformat/JavaCodeUnformatted.test");
+		gradleRunner().withArguments("independent").build();
+		assertFile("test.java").sameAsResource("java/googlejavaformat/JavaCodeFormatted.test");
+	}
+}