Add m2e support

This closes #1413

Author: kwin

plugin-maven/build.gradle

@@ -76,6 +76,7 @@ dependencies {
 	implementation "com.diffplug.durian:durian-collect:${VER_DURIAN}"
 	implementation("org.codehaus.plexus:plexus-resources:${VER_PLEXUS_RESOURCES}")
 	implementation "org.eclipse.jgit:org.eclipse.jgit:${VER_JGIT}"
+	implementation 'org.sonatype.plexus:plexus-build-api:0.0.7'
 
 	testImplementation project(":testlib")
 	testImplementation "org.junit.jupiter:junit-jupiter:${VER_JUNIT}"

plugin-maven/src/main/java/com/diffplug/spotless/maven/AbstractSpotlessMojo.java

@@ -88,6 +88,9 @@ public abstract class AbstractSpotlessMojo extends AbstractMojo {
 	@Component
 	private ResourceManager resourceManager;
 
+	@Component
+	protected BuildContext buildContext;
+
 	@Parameter(defaultValue = "${mojoExecution.goal}", required = true, readonly = true)
 	private String goal;
 
@@ -344,10 +347,13 @@ private UpToDateChecker createUpToDateChecker(Iterable<Formatter> formatters) {
 			Path targetDir = project.getBasedir().toPath().resolve(project.getBuild().getDirectory());
 			indexFile = targetDir.resolve(DEFAULT_INDEX_FILE_NAME);
 		}
+		final UpToDateChecker checker;
 		if (upToDateChecking != null && upToDateChecking.isEnabled()) {
 			getLog().info("Up-to-date checking enabled");
-			return UpToDateChecker.forProject(project, indexFile, formatters, getLog());
+			checker = UpToDateChecker.forProject(project, indexFile, formatters, getLog());
+		} else {
+			checker = UpToDateChecker.noop(project, indexFile, getLog());
 		}
-		return UpToDateChecker.noop(project, indexFile, getLog());
+		return UpToDateChecker.wrapWithBuildContext(checker, buildContext);
 	}
 }

plugin-maven/src/main/java/com/diffplug/spotless/maven/SpotlessApplyMojo.java

@@ -45,6 +45,7 @@ protected void process(Iterable<File> files, Formatter formatter, UpToDateChecke
 				PaddedCell.DirtyState dirtyState = PaddedCell.calculateDirtyState(formatter, file);
 				if (!dirtyState.isClean() && !dirtyState.didNotConverge()) {
 					dirtyState.writeCanonicalTo(file);
+					buildContext.refresh(file);
 				}
 			} catch (IOException e) {
 				throw new MojoExecutionException("Unable to format file " + file, e);

plugin-maven/src/main/java/com/diffplug/spotless/maven/incremental/UpToDateChecker.java

@@ -19,6 +19,7 @@
 
 import org.apache.maven.plugin.logging.Log;
 import org.apache.maven.project.MavenProject;
+import org.sonatype.plexus.build.incremental.BuildContext;
 
 import com.diffplug.spotless.Formatter;
 
@@ -37,4 +38,25 @@ static UpToDateChecker noop(MavenProject project, Path indexFile, Log log) {
 	static UpToDateChecker forProject(MavenProject project, Path indexFile, Iterable<Formatter> formatters, Log log) {
 		return IndexBasedChecker.create(project, indexFile, formatters, log);
 	}
+	
+	static UpToDateChecker wrapWithBuildContext(UpToDateChecker delegate, BuildContext buildContext) {
+		return new UpToDateChecker() {
+		
+			@Override
+			public void setUpToDate(Path file) {
+				delegate.setUpToDate(file);
+			}
+
+			@Override
+			public boolean isUpToDate(Path file) {
+				return !buildContext.hasDelta(file.toFile()) || delegate.isUpToDate(file);
+			}
+
+			@Override
+			public void close() {
+				delegate.close();
+			}
+		};
+	}
+	
 }

plugin-maven/src/main/resources/META-INF/m2e/lifecycle-mapping-metadata.xml

@@ -0,0 +1,32 @@
+<!--
+  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.
+  -->
+<!-- metadata for m2e: https://www.eclipse.org/m2e/documentation/m2e-making-maven-plugins-compat.html -->
+<lifecycleMappingMetadata>
+    <pluginExecutions>
+        <pluginExecution>
+            <pluginExecutionFilter>
+                <goals>
+                    <goal>apply</goal>
+                    <goal>check</goal>
+                </goals>
+            </pluginExecutionFilter>
+            <action>
+                <execute>
+                    <runOnIncremental>true</runOnIncremental>
+                    <runOnConfiguration>false</runOnConfiguration>
+                </execute>
+            </action>
+        </pluginExecution>
+    </pluginExecutions>
+</lifecycleMappingMetadata>