Flag to fail as in maven-enforcer-plugin

src/it/setup-custom-toolchain/pom.xml

@@ -38,7 +38,7 @@ under the License.
     <dependency>
       <groupId>org.apache.maven</groupId>
       <artifactId>maven-core</artifactId>
-      <version>3.0.5</version>
+      <version>3.8.1</version>
     </dependency>
 
     <!-- plugin API and plugin-tools -->

src/it/skip-fail/invoker.properties

@@ -0,0 +1,20 @@
+# 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 = compile
+# cannot run this IT with Maven 2 since required --toolchains option was added in 3.0-alpha-3: see MNG-3714
+invoker.maven.version = 3.0+

src/it/skip-fail/pom.xml

@@ -0,0 +1,67 @@
+<?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.toolchains.its</groupId>
+  <artifactId>skip-fail</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <packaging>jar</packaging>
+
+  <name>maven-toolchains-plugin IT: missing toolchain test</name>
+  <description>
+    Check that toolchain requirements are checked and not covered as expected
+  </description>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-toolchains-plugin</artifactId>
+        <version>@project.version@</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>toolchain</goal>
+            </goals>
+          </execution>
+        </executions>
+        <configuration>
+          <toolchains>
+            <jdk/>
+            <fake-type>
+              <attribute>value</attribute>
+              <other-attribute>other-value</other-attribute>
+            </fake-type>
+            <another-fake-type/>
+          </toolchains>
+          <fail>false</fail>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/skip-fail/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.
+ */
+
+content = new File( basedir, 'build.log' ).text
+
+assert content.indexOf( "MojoFailureException: Cannot find matching toolchain definitions for the following toolchain types:" ) > 0

src/main/java/org/apache/maven/plugins/toolchain/ToolchainMojo.java

@@ -70,6 +70,13 @@ public class ToolchainMojo extends AbstractMojo {
     @Parameter(required = true)
     private ToolchainsRequirement toolchains;
 
+    /**
+     * Flag to fail the build if toolchain requirements not met.
+     * @since 3.0.1
+     */
+    @Parameter( defaultValue = "true" )
+    private boolean fail;
+
     @Override
     public void execute() throws MojoExecutionException, MojoFailureException {
         if (toolchains == null) {
@@ -99,10 +106,17 @@ public void execute() throws MojoExecutionException, MojoFailureException {
                 buff.append(getToolchainRequirementAsString(type, toolchains.getParams(type)));
             }
 
-            getLog().error(buff.toString());
+            if ( fail )
+            {
+                getLog().error( buff.toString() );
 
-            throw new MojoFailureException(buff.toString() + System.lineSeparator()
-                    + "Please make sure you define the required toolchains in your ~/.m2/toolchains.xml file.");
+                throw new MojoFailureException( buff.toString() + System.lineSeparator()
+                    + "Please make sure you define the required toolchains in your ~/.m2/toolchains.xml file." );
+            }
+            else
+            {
+                getLog().warn( buff.toString() );
+            }
         }
     }