feat: add support for minimal-update option in maven plugin

modules/openapi-generator-maven-plugin/src/main/java/org/openapitools/codegen/plugin/CodeGenMojo.java

@@ -321,6 +321,12 @@ public class CodeGenMojo extends AbstractMojo {
     @Parameter(name = "generateAliasAsModel", property = "openapi.generator.maven.plugin.generateAliasAsModel")
     private Boolean generateAliasAsModel;
 
+    /**
+     * Only write output files that have changed.
+     */
+    @Parameter(name = "minimalUpdate", property = "openapi.generator.maven.plugin.minimalUpdate")
+    private Boolean minimalUpdate;
+
     /**
      * A map of language-specific parameters as passed with the -c option to the command line
      */
@@ -698,6 +704,10 @@ public void execute() throws MojoExecutionException {
                 configurator.setGenerateAliasAsModel(generateAliasAsModel);
             }
 
+            if (minimalUpdate != null) {
+                configurator.setEnableMinimalUpdate(minimalUpdate);
+            }
+
             if (isNotEmpty(generatorName)) {
                 configurator.setGeneratorName(generatorName);
             } else {

modules/openapi-generator-maven-plugin/src/test/java/org/openapitools/codegen/plugin/CodeGenMojoTest.java

@@ -38,6 +38,7 @@
 import java.nio.file.Path;
 import java.nio.file.StandardOpenOption;
 import java.util.Comparator;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -88,6 +89,17 @@ private void testCommonConfiguration(String profile) throws Exception {
         assertEquals("joda", configOptions.get("dateLibrary"));
     }
 
+    public void testMinimalUpdateConfiguration() throws Exception {
+        // GIVEN
+        CodeGenMojo mojo = loadMojo(newTempFolder(), "src/test/resources/minimal-update", null);
+
+        // WHEN
+        mojo.execute();
+
+        // THEN
+        assertEquals(Boolean.TRUE, getVariableValueFromObject(mojo, "minimalUpdate"));
+    }
+
     public void testHashGenerationFileContainsExecutionId() throws Exception {
         // GIVEN
         final Path tempDir = newTempFolder();
@@ -136,6 +148,50 @@ public void testSkipRegenerationForClasspathSpecFileNoChange() throws Exception
         assertFalse("src directory should not have been regenerated", Files.exists(generatedDir.resolve("src")));
     }
 
+    public void testMinimalUpdate() throws Exception {
+        //GIVEN
+        /* Set up the mojo */
+        final Path tempDir = newTempFolder();
+        final CodeGenMojo mojo = loadMojo(tempDir, "src/test/resources/minimal-update", null, "executionId");
+
+        /* Perform an initial generation */
+        mojo.execute();
+
+        /* Collect last modified times of generated files */
+        final Path generatedDir = tempDir.resolve("target/generated-sources/minimal-update");
+        assertTrue("Generated directory should exist", Files.exists(generatedDir));
+
+        Map<Path, Long> lastModifiedTimes = new HashMap<>();
+        try (Stream<Path> files = Files.walk(generatedDir)) {
+            files
+                .filter(Files::isRegularFile)
+                .filter(path -> !path.getFileName().toString().endsWith(".sha256"))
+                .filter(path -> !path.getFileName().toString().equals("FILES"))
+                .forEach(file -> {
+                    try {
+                        lastModifiedTimes.put(file, Files.getLastModifiedTime(file).toMillis());
+                    } catch (IOException e) {
+                        throw new RuntimeException(e);
+                    }
+                });
+        }
+        assertTrue("Should have recorded last modified times for more than 3 files", lastModifiedTimes.size() > 3);
+
+        // WHEN
+        /* Execute the mojo again */
+        mojo.execute();
+
+        // THEN
+        /* Verify that file modification times haven't changed (files weren't touched) */
+        for (Map.Entry<Path, Long> entry : lastModifiedTimes.entrySet()) {
+            Path file = entry.getKey();
+            Long originalTime = entry.getValue();
+            Long currentTime = Files.getLastModifiedTime(file).toMillis();
+            assertEquals("File " + file + " should not have been modified (minimal update should skip unchanged files)",
+                originalTime, currentTime);
+        }
+    }
+
     /**
      * For a Pom file which refers to an input file which will be on the classpath, as opposed to a file path,
      * test that the generated source is regenerated when the hash has changed.
@@ -242,7 +298,7 @@ public void test_skipIfSpecIsUnchanged_recognizesUpdatesInExternalReferencedFile
         final Path generatedDir = tempDir.resolve("target/generated-sources/issue-16489");
         final Path hashFile = generatedDir.resolve(".openapi-generator/petstore.yaml-default.sha256");
         final CodeGenMojo mojo = loadMojo(tempDir, "src/test/resources/issue-16489", null);
-        mojo.execute(); // Perform an initial generation 
+        mojo.execute(); // Perform an initial generation
         var currentHash = Files.readString(hashFile);   // read hash
         FileUtils.deleteDirectory(generatedDir.resolve("src").toFile());    // Remove the generated source
         Files.writeString(  // change schema definition in external file

modules/openapi-generator-maven-plugin/src/test/resources/minimal-update/pom.xml

@@ -0,0 +1,52 @@
+<!--
+  ~ Copyright 2020, 2021 OpenAPI-Generator Contributors (https://openapi-generator.tech)
+  ~
+  ~ Licensed 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>
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>minimal.update.test</groupId>
+    <artifactId>minimal-update-test</artifactId>
+    <packaging>jar</packaging>
+    <version>1.0.0-SNAPSHOT</version>
+    <name>OpenAPI Generator Minimal Update Test</name>
+    <url>https://openapi-generator.tech/</url>
+    <build>
+        <finalName>minimal-update-test</finalName>
+        <plugins>
+            <plugin>
+                <groupId>org.openapitools</groupId>
+                <artifactId>openapi-generator-maven-plugin</artifactId>
+                <configuration>
+                    <inputSpec>petstore-on-classpath.yaml</inputSpec>
+                    <generatorName>spring</generatorName>
+                    <output>${basedir}/target/generated-sources/minimal-update</output>
+                    <minimalUpdate>true</minimalUpdate>
+                    <configOptions>
+                        <hideGenerationTimestamp>true</hideGenerationTimestamp>
+                    </configOptions>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>executionId</id>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>generate</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>