First commit to discuss the idea

Author: blacelle

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

@@ -0,0 +1,24 @@
+package com.diffplug.spotless.maven;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class ImpactedFilesTracker {
+	protected final AtomicInteger nbChecked = new AtomicInteger();
+	protected final AtomicInteger nbCleaned = new AtomicInteger();
+
+	public void checked() {
+		nbChecked.incrementAndGet();
+	}
+
+	public int getChecked() {
+		return nbChecked.get();
+	}
+
+	public void cleaned() {
+		nbCleaned.incrementAndGet();
+	}
+
+	public int getCleaned() {
+		return nbCleaned.get();
+	}
+}

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

@@ -33,6 +33,8 @@ public class SpotlessApplyMojo extends AbstractSpotlessMojo {
 
 	@Override
 	protected void process(Iterable<File> files, Formatter formatter, UpToDateChecker upToDateChecker) throws MojoExecutionException {
+		ImpactedFilesTracker impactedFilesTracker = new ImpactedFilesTracker();
+
 		for (File file : files) {
 			if (upToDateChecker.isUpToDate(file.toPath())) {
 				if (getLog().isDebugEnabled()) {
@@ -42,16 +44,22 @@ protected void process(Iterable<File> files, Formatter formatter, UpToDateChecke
 			}
 
 			try {
+				impactedFilesTracker.checked();
 				PaddedCell.DirtyState dirtyState = PaddedCell.calculateDirtyState(formatter, file);
 				if (!dirtyState.isClean() && !dirtyState.didNotConverge()) {
+					getLog().info(String.format("Writing clean file: %s", file));
 					dirtyState.writeCanonicalTo(file);
 					buildContext.refresh(file);
+					impactedFilesTracker.cleaned();
 				}
 			} catch (IOException e) {
 				throw new MojoExecutionException("Unable to format file " + file, e);
 			}
 
 			upToDateChecker.setUpToDate(file.toPath());
 		}
+
+		// We print the number of considered files which is useful when ratchetFrom is setup
+		getLog().info(String.format("A formatter with %s steps cleaned: %s files (for %s considered)", formatter.getSteps().size(), impactedFilesTracker.getCleaned(), impactedFilesTracker.getChecked()));
 	}
 }