Display the command formatting all the files when the validation fails

core/src/main/java/com/cosium/code/format/ValidateCodeFormat.java

@@ -1,27 +1,49 @@
 package com.cosium.code.format;
 
 import com.cosium.code.format.formatter.CodeFormatters;
+import com.cosium.code.format.maven.MavenDocumentation;
 import com.cosium.code.format_spi.CodeFormatter;
 import com.cosium.code.format_spi.FileExtension;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import org.apache.maven.plugin.MojoFailureException;
+import org.apache.maven.plugin.descriptor.PluginDescriptor;
 import org.apache.maven.plugins.annotations.LifecyclePhase;
 import org.apache.maven.plugins.annotations.Mojo;
+import org.apache.maven.plugins.annotations.Parameter;
 
 /**
  * @author Réda Housni Alaoui
  */
 @Mojo(name = "validate-code-format", defaultPhase = LifecyclePhase.VERIFY, threadSafe = true)
 public class ValidateCodeFormat extends AbstractFormatMojo {
+
+  @Parameter(readonly = true, defaultValue = "${plugin}")
+  private PluginDescriptor pluginDescriptor;
+
+  @Parameter(readonly = true, defaultValue = "${session.executionRootDirectory}")
+  private String executionRootDirectory;
+
   @Override
   protected void process(CodeFormatters codeFormatters, Path path) throws MojoFailureException {
     if (validate(codeFormatters, path)) {
       return;
     }
-    throw new MojoFailureException(path + " is not correctly formatted !");
+    throw new MojoFailureException(
+        path
+            + " is not correctly formatted !"
+            + System.lineSeparator()
+            + "Run '"
+            + mavenDocumentation().createFormatCodeCommand()
+            + "' to format all the files.");
+  }
+
+  private MavenDocumentation mavenDocumentation() {
+    return new MavenDocumentation(
+        this::getLog, pluginDescriptor, baseDir(), gitBaseDir(), Paths.get(executionRootDirectory));
   }
 
   private boolean validate(CodeFormatters codeFormatters, Path path) {

core/src/main/java/com/cosium/code/format/maven/MavenDocumentation.java

@@ -0,0 +1,54 @@
+package com.cosium.code.format.maven;
+
+import static java.util.Objects.requireNonNull;
+
+import java.io.File;
+import java.nio.file.Path;
+import java.util.function.Supplier;
+import org.apache.maven.plugin.descriptor.PluginDescriptor;
+import org.apache.maven.plugin.logging.Log;
+
+/**
+ * @author Réda Housni Alaoui
+ */
+public class MavenDocumentation {
+
+  private final MavenWrapperExecutables wrapperExecutables;
+  private final PluginDescriptor pluginDescriptor;
+  private final Path executionRootDirectory;
+
+  public MavenDocumentation(
+      Supplier<Log> log,
+      PluginDescriptor pluginDescriptor,
+      Path baseDir,
+      Path gitBaseDir,
+      Path executionRootDirectory) {
+    this.wrapperExecutables = new MavenWrapperExecutables(log, baseDir, gitBaseDir);
+    this.pluginDescriptor = requireNonNull(pluginDescriptor);
+    this.executionRootDirectory = requireNonNull(executionRootDirectory);
+  }
+
+  /**
+   * @return The command formatting all the files, to be run from the execution root directory
+   */
+  public String createFormatCodeCommand() {
+    return "%s %s:format-code".formatted(createMavenCommand(), pluginDescriptor.getGoalPrefix());
+  }
+
+  private String createMavenCommand() {
+    return wrapperExecutables.stream(false)
+        .filter(MavenExecutable::isValid)
+        .findFirst()
+        .map(MavenExecutable::path)
+        .map(this::createWrapperCommand)
+        .orElse("mvn");
+  }
+
+  private String createWrapperCommand(Path wrapperPath) {
+    Path directory = executionRootDirectory.toAbsolutePath().normalize();
+    if (!wrapperPath.startsWith(directory)) {
+      return wrapperPath.toString();
+    }
+    return "." + File.separator + directory.relativize(wrapperPath);
+  }
+}

core/src/test/java/com/cosium/code/format/AbstractMavenModuleTest.java

@@ -44,6 +44,16 @@ public void GIVEN_bad_formatted_files_WHEN_format_code_THEN_all_files_should_hav
     assertMatchExpected(badFormatJava);
   }
 
+  @MavenPluginTest
+  public void
+      GIVEN_bad_formatted_file_WHEN_validating_THEN_the_command_formatting_all_files_is_displayed()
+          throws Exception {
+    mavenExecution()
+        .withCliOptions(goalCliOption("validate-code-format"))
+        .execute()
+        .assertLogText("Run 'mvn git-code-format:format-code' to format all the files.");
+  }
+
   @MavenPluginTest
   public void
       GIVEN_bad_formatted_file_WHEN_adding_and_committing_it_THEN_it_should_have_correct_format()

core/src/test/java/com/cosium/code/format/MavenWrapperTest.java

@@ -5,6 +5,7 @@
 import io.takari.maven.testing.executor.MavenRuntime;
 import io.takari.maven.testing.executor.MavenVersions;
 import io.takari.maven.testing.executor.junit.MavenPluginTest;
+import java.io.File;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
@@ -104,6 +105,21 @@ public void GIVEN_a_maven_wrapper_WHEN_committing_THEN_the_wrapper_formats_the_s
         .isEqualTo("public class BadFormat {\n" + "\n" + "  void a() {}\n" + "}\n");
   }
 
+  @MavenPluginTest
+  public void
+      GIVEN_a_maven_wrapper_WHEN_the_validation_fails_THEN_the_wrapper_is_the_command_to_run()
+          throws Exception {
+    installMavenWrapper(projectRoot());
+
+    buildMavenExecution(projectRoot())
+        .withCliOptions(goalCliOption("validate-code-format"))
+        .execute()
+        .assertLogText(
+            "Run '."
+                + File.separator
+                + "mvnw git-code-format:format-code' to format all the files.");
+  }
+
   private void write(String sourceName, String content) throws IOException {
     Files.write(
         resolveRelativelyToProjectRoot(sourceName), content.getBytes(StandardCharsets.UTF_8));