feat: add a maven plugin

README.md

@@ -120,6 +120,35 @@ usage: openapi-diff <old> <new>
     --warn                      Print warning information
 ```
 
+## Maven Plugin
+
+Add openapi-diff to your POM to show diffs when you test your Maven project. You may opt to throw an error if you have broken backwards compatibility or if your API has changed.  
+
+```xml
+<plugin>
+  <groupId>org.openapitools.openapidiff</groupId>
+  <artifactId>openapi-diff-maven</artifactId>
+  <version>${openapi-diff-version}</version>
+  <executions>
+    <execution>
+      <goals>
+        <goal>diff</goal>
+      </goals>
+      <configuration>
+        <!-- Reference specification (perhaps your prod schema) -->
+        <oldSpec>https://petstore3.swagger.io/api/v3/openapi.json</oldSpec>
+        <!-- Specification generated by your project in the compile phase -->
+        <newSpec>${project.basedir}/target/openapi.yaml</newSpec>
+        <!-- Fail only if API changes broke backward compatibility (default: false) -->
+        <failOnIncompatible>true</failOnIncompatible>
+        <!-- Fail if API changed (default: false) -->
+        <failOnChanged>true</failOnIncompatible>
+      </configuration>
+    </execution>
+  </executions>
+</plugin>
+```
+
 ## Direct Invocation
 
 ```java

maven/pom.xml

@@ -0,0 +1,64 @@
+<?xml version="1.0"?>
+<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.openapitools.openapidiff</groupId>
+    <artifactId>openapi-diff-parent</artifactId>
+    <version>2.0.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>openapi-diff-maven</artifactId>
+  <packaging>jar</packaging>
+
+  <name>openapi-diff-maven</name>
+  <description>Maven plugin for openapi-diff</description>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.apache.maven</groupId>
+      <artifactId>maven-plugin-api</artifactId>
+      <version>3.6.0</version>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.apache.maven</groupId>
+      <artifactId>maven-core</artifactId>
+      <version>3.6.0</version>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.apache.maven.plugin-tools</groupId>
+      <artifactId>maven-plugin-annotations</artifactId>
+      <version>3.4</version>
+      <scope>provided</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.openapitools.openapidiff</groupId>
+      <artifactId>openapi-diff-core</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <pluginManagement>
+      <plugins>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-plugin-plugin</artifactId>
+          <version>3.6.0</version>
+        </plugin>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-site-plugin</artifactId>
+          <version>3.8.2</version>
+        </plugin>
+      </plugins>
+    </pluginManagement>
+  </build>
+</project>

maven/src/main/java/org/openapitools/openapidiff/maven/ApiChangedException.java

@@ -0,0 +1,9 @@
+package org.openapitools.openapidiff.maven;
+
+import org.apache.maven.plugin.MojoFailureException;
+
+public class ApiChangedException extends MojoFailureException {
+  public ApiChangedException(String message) {
+    super(message);
+  }
+}

maven/src/main/java/org/openapitools/openapidiff/maven/BackwardIncompatibilityException.java

@@ -0,0 +1,9 @@
+package org.openapitools.openapidiff.maven;
+
+import org.apache.maven.plugin.MojoFailureException;
+
+class BackwardIncompatibilityException extends MojoFailureException {
+  public BackwardIncompatibilityException(String message) {
+    super(message);
+  }
+}

maven/src/main/java/org/openapitools/openapidiff/maven/OpenApiDiffMojo.java

@@ -0,0 +1,45 @@
+package org.openapitools.openapidiff.maven;
+
+import org.apache.maven.plugin.AbstractMojo;
+import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugin.MojoFailureException;
+import org.apache.maven.plugins.annotations.LifecyclePhase;
+import org.apache.maven.plugins.annotations.Mojo;
+import org.apache.maven.plugins.annotations.Parameter;
+import org.openapitools.openapidiff.core.OpenApiCompare;
+import org.openapitools.openapidiff.core.model.ChangedOpenApi;
+import org.openapitools.openapidiff.core.output.ConsoleRender;
+
+/** A Maven Mojo that diffs two OpenAPI specifications and reports on differences. */
+@Mojo(name = "diff", defaultPhase = LifecyclePhase.TEST)
+public class OpenApiDiffMojo extends AbstractMojo {
+  @Parameter(property = "oldSpec")
+  String oldSpec;
+
+  @Parameter(property = "newSpec")
+  String newSpec;
+
+  @Parameter(property = "failOnIncompatible", defaultValue = "false")
+  Boolean failOnIncompatible = false;
+
+  @Parameter(property = "failOnChanged", defaultValue = "false")
+  Boolean failOnChanged = false;
+
+  @Override
+  public void execute() throws MojoExecutionException, MojoFailureException {
+    try {
+      final ChangedOpenApi diff = OpenApiCompare.fromLocations(oldSpec, newSpec);
+      getLog().info(new ConsoleRender().render(diff));
+
+      if (failOnIncompatible && diff.isIncompatible()) {
+        throw new BackwardIncompatibilityException("The API changes broke backward compatibility");
+      }
+
+      if (failOnChanged && diff.isDifferent()) {
+        throw new ApiChangedException("The API changed");
+      }
+    } catch (RuntimeException e) {
+      throw new MojoExecutionException("Unexpected error", e);
+    }
+  }
+}

maven/src/test/java/org/openapitools/openapidiff/maven/OpenApiDiffMojoTest.java

@@ -0,0 +1,78 @@
+package org.openapitools.openapidiff.maven;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.io.File;
+import org.apache.maven.plugin.MojoExecutionException;
+import org.junit.jupiter.api.Test;
+
+class OpenApiDiffMojoTest {
+  @Test
+  void Should_NotThrow_When_SpecHasNoChanges() {
+    final String oldSpec = new File("src/test/resources/oldspec.yaml").getAbsolutePath();
+
+    final OpenApiDiffMojo mojo = new OpenApiDiffMojo();
+    mojo.oldSpec = oldSpec;
+    mojo.newSpec = oldSpec;
+    mojo.failOnIncompatible = true;
+
+    assertDoesNotThrow(mojo::execute);
+  }
+
+  @Test
+  void Should_NotThrow_When_SpecIsCompatible() {
+    final OpenApiDiffMojo mojo = new OpenApiDiffMojo();
+    mojo.oldSpec = new File("src/test/resources/oldspec.yaml").getAbsolutePath();
+    mojo.newSpec = new File("src/test/resources/newspec.yaml").getAbsolutePath();
+    mojo.failOnIncompatible = true;
+
+    assertDoesNotThrow(mojo::execute);
+  }
+
+  @Test
+  void Should_Throw_When_SpecIsDifferent() {
+    final OpenApiDiffMojo mojo = new OpenApiDiffMojo();
+    mojo.oldSpec = new File("src/test/resources/oldspec.yaml").getAbsolutePath();
+    mojo.newSpec = new File("src/test/resources/newspec.yaml").getAbsolutePath();
+    mojo.failOnChanged = true;
+
+    assertThrows(ApiChangedException.class, mojo::execute);
+  }
+
+  @Test
+  void Should_MojoExecutionException_When_MissingOldSpec() {
+    final OpenApiDiffMojo mojo = new OpenApiDiffMojo();
+    mojo.oldSpec = new File("DOES_NOT_EXIST").getAbsolutePath();
+    mojo.newSpec = new File("src/test/resources/newspec.yaml").getAbsolutePath();
+
+    assertThrows(MojoExecutionException.class, mojo::execute);
+  }
+
+  @Test
+  void Should_MojoExecutionException_When_MissingNewSpec() {
+    final OpenApiDiffMojo mojo = new OpenApiDiffMojo();
+    mojo.oldSpec = new File("src/test/resources/oldspec.yaml").getAbsolutePath();
+    mojo.newSpec = new File("DOES_NOT_EXIST").getAbsolutePath();
+
+    assertThrows(MojoExecutionException.class, mojo::execute);
+  }
+
+  @Test
+  void Should_NotThrow_When_DefaultsAndSpecIsIncompatible() {
+    final OpenApiDiffMojo mojo = new OpenApiDiffMojo();
+    mojo.oldSpec = new File("src/test/resources/newspec.yaml").getAbsolutePath();
+    mojo.newSpec = new File("src/test/resources/oldspec.yaml").getAbsolutePath();
+
+    assertDoesNotThrow(mojo::execute);
+  }
+
+  @Test
+  void Should_BackwardIncompatibilityException_When_WantsExceptionAndSpecIsIncompatible() {
+    final OpenApiDiffMojo mojo = new OpenApiDiffMojo();
+    mojo.oldSpec = new File("src/test/resources/newspec.yaml").getAbsolutePath();
+    mojo.newSpec = new File("src/test/resources/oldspec.yaml").getAbsolutePath();
+    mojo.failOnIncompatible = true;
+
+    assertThrows(BackwardIncompatibilityException.class, mojo::execute);
+  }
+}

maven/src/test/resources/newspec.yaml

@@ -0,0 +1,15 @@
+---
+openapi: 3.0.3
+info:
+  title: Generated API
+  version: "1.0"
+paths:
+  /hello:
+    get:
+      responses:
+        "200":
+          description: OK
+          content:
+            text/plain:
+              schema:
+                type: string

maven/src/test/resources/oldspec.yaml

@@ -0,0 +1,6 @@
+---
+openapi: 3.0.3
+info:
+  title: Generated API
+  version: "1.0"
+paths: {}

pom.xml

@@ -3,6 +3,7 @@
     <modules>
         <module>core</module>
         <module>cli</module>
+        <module>maven</module>
     </modules>
 
     <groupId>org.openapitools.openapidiff</groupId>
@@ -31,6 +32,11 @@
             <email>[email protected]</email>
             <url>https://github.com/joschi</url>
         </developer>
+        <developer>
+            <name>Josh Kellendonk</name>
+            <email>[email protected]</email>
+            <url>https://github.com/misterjoshua</url>
+        </developer>
     </developers>
 
     <issueManagement>