Introduce parameter failOnMismatchedAllowedViolationsCount

src/it/check-fail-with-mismatch-violation-count/invoker.properties

@@ -0,0 +1,19 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+
+invoker.goals=verify
+invoker.buildResult=failure

src/it/check-fail-with-mismatch-violation-count/pom.xml

@@ -0,0 +1,57 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one
+  ~ or more contributor license agreements.  See the NOTICE file
+  ~ distributed with this work for additional information
+  ~ regarding copyright ownership.  The ASF licenses this file
+  ~ to you 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.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.apache.maven.plugins.checkstyle</groupId>
+  <artifactId>check-fail</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <packaging>jar</packaging>
+
+  <url>http://maven.apache.org/</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <checkstyle.violation.ignore>NewlineAtEndOfFile</checkstyle.violation.ignore>
+    <checkstyle.maxAllowedViolations>314</checkstyle.maxAllowedViolations>
+    <checkstyle.failOnMismatchedAllowedViolationsCount>true</checkstyle.failOnMismatchedAllowedViolationsCount>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-checkstyle-plugin</artifactId>
+        <version>@project.version@</version>
+        <executions>
+          <execution>
+            <id>check</id>
+            <goals>
+              <goal>check</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/check-fail-with-mismatch-violation-count/src/main/java/org/MyClass.java

@@ -0,0 +1,27 @@
+package org;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+/**
+ * My class.
+ */
+public class MyClass
+{
+}

src/it/check-fail-with-mismatch-violation-count/src/main/java/org/package-info.java

@@ -0,0 +1,23 @@
+/**
+ * Nothing very important here, only a file for checkstyle rule PackageInfo.
+ */
+package org;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */

src/it/check-fail-with-mismatch-violation-count/verify.groovy

@@ -0,0 +1,22 @@
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+def buildLog = new File( basedir, 'build.log' )
+
+assert buildLog.text.contains( "The number of violations (1) is not equal to the maximum number of allowed violations (314)" )

src/main/java/org/apache/maven/plugins/checkstyle/CheckstyleViolationCheckMojo.java

@@ -108,6 +108,19 @@ public class CheckstyleViolationCheckMojo extends AbstractMojo {
     @Parameter(property = "checkstyle.failOnViolation", defaultValue = "true")
     private boolean failOnViolation;
 
+    /**
+     * Fail the build when the number of violations is not equal to {@link #maxAllowedViolations}.
+     * <p>This prevents the following scenario:
+     * <ul>
+     *   <li>some changes reduce the checkstyle count but maxAllowedViolations is not updated</li>
+     *   <li>some other changes introduces new violations but the build does not fail, as the count left some margin for error</li>
+     * </ul>
+     *
+     * * @since 3.6.1
+     */
+    @Parameter(property = "checkstyle.failOnMismatchedAllowedViolationsCount", defaultValue = "false")
+    private boolean failOnMismatchedAllowedViolationsCount;
+
     /**
      * The maximum number of allowed violations. The execution fails only if the
      * number of violations is above this limit.
@@ -599,6 +612,10 @@ public void execute() throws MojoExecutionException, MojoFailureException {
                 }
 
                 getLog().warn("checkstyle:check violations detected but failOnViolation set to false");
+            } else if (failOnMismatchedAllowedViolationsCount && violationCount != maxAllowedViolations) {
+                throw new MojoFailureException("The number of violations (" + violationCount
+                        + ") is not equal to the maximum number of allowed violations (" + maxAllowedViolations
+                        + ").");
             }
             if (logViolationCountToConsole) {
                 if (maxAllowedViolations > 0) {