Make rewrite-maven-plugin search for Kotlin source files in src/*/java if src/*/kotlin does not exist

src/main/java/org/openrewrite/maven/MavenMojoProjectParser.java

@@ -31,6 +31,7 @@
 import org.apache.maven.settings.crypto.SettingsDecryptionRequest;
 import org.apache.maven.settings.crypto.SettingsDecryptionResult;
 import org.codehaus.plexus.util.xml.Xpp3Dom;
+import org.jetbrains.annotations.NotNull;
 import org.jspecify.annotations.Nullable;
 import org.openrewrite.ExecutionContext;
 import org.openrewrite.ParseExceptionResult;
@@ -242,7 +243,7 @@ private SourceFile logParseErrors(SourceFile source) {
         source.getMarkers().findFirst(ParseExceptionResult.class).ifPresent(e -> {
             if (firstWarningLogged.compareAndSet(false, true)) {
                 logger.warn("There were problems parsing some source files" +
-                            (mavenSession.getRequest().isShowErrors() ? "" : ", run with --errors to see full stack traces"));
+                        (mavenSession.getRequest().isShowErrors() ? "" : ", run with --errors to see full stack traces"));
             }
             logger.warn("There were problems parsing " + source.getSourcePath());
             if (mavenSession.getRequest().isShowErrors()) {
@@ -388,16 +389,16 @@ private Stream<SourceFile> processMainSources(
         // Some annotation processors output generated sources to the /target directory. These are added for parsing but
         // should be filtered out of the final SourceFile list.
         List<Path> generatedSourcePaths = listJavaSources(mavenProject.getBasedir().toPath().resolve(mavenProject.getBuild().getDirectory()));
+        String mavenSourceDirectory = mavenProject.getBuild().getSourceDirectory();
         List<Path> mainJavaSources = Stream.concat(
                 generatedSourcePaths.stream(),
-                listJavaSources(mavenProject.getBasedir().toPath().resolve(mavenProject.getBuild().getSourceDirectory())).stream()
+                listJavaSources(mavenProject.getBasedir().toPath().resolve(mavenSourceDirectory)).stream()
         ).collect(toList());
 
         alreadyParsed.addAll(mainJavaSources);
 
         // scan Kotlin files
-        String kotlinSourceDir = getKotlinDirectory(mavenProject.getBuild().getSourceDirectory());
-        List<Path> mainKotlinSources = (kotlinSourceDir != null) ? listKotlinSources(mavenProject.getBasedir().toPath().resolve(kotlinSourceDir)) : Collections.emptyList();
+        List<Path> mainKotlinSources = listKotlinSources(mavenProject, mavenSourceDirectory);
         alreadyParsed.addAll(mainKotlinSources);
 
         logInfo(mavenProject, "Parsing source files");
@@ -465,8 +466,8 @@ private Stream<SourceFile> processTestSources(
         alreadyParsed.addAll(testJavaSources);
 
         // scan Kotlin files
-        String kotlinSourceDir = getKotlinDirectory(mavenProject.getBuild().getTestSourceDirectory());
-        List<Path> testKotlinSources = (kotlinSourceDir != null) ? listKotlinSources(mavenProject.getBasedir().toPath().resolve(kotlinSourceDir)) : Collections.emptyList();
+        String mavenTestSourceDirectory = mavenProject.getBuild().getTestSourceDirectory();
+        List<Path> testKotlinSources = listKotlinSources(mavenProject, mavenTestSourceDirectory);
         alreadyParsed.addAll(testKotlinSources);
 
         Stream<SourceFile> parsedJava = Stream.empty();
@@ -493,6 +494,11 @@ private Stream<SourceFile> processTestSources(
                 .map(addProvenance(baseDir, markers, null));
     }
 
+    private @NotNull List<Path> listKotlinSources(MavenProject mavenProject, String fallbackSourceDirectory) throws MojoExecutionException {
+        String kotlinSourceDir = getKotlinDirectory(fallbackSourceDirectory);
+        return listSources(mavenProject.getBasedir().toPath().resolve(kotlinSourceDir != null ? kotlinSourceDir : fallbackSourceDirectory), ".kt");
+    }
+
     private @Nullable String getKotlinDirectory(@Nullable String sourceDirectory) {
         if (sourceDirectory == null) {
             return null;
@@ -582,7 +588,7 @@ public Map<MavenProject, Xml.Document> parseMaven(List<MavenProject> mavenProjec
                     throw new MojoFailureException(
                             mavenProject,
                             "Failed to parse or resolve the Maven POM file or one of its dependencies; " +
-                            "We can not reliably continue without this information.",
+                                    "We can not reliably continue without this information.",
                             parseExceptionResult.get().getMessage());
                 }
                 projectMap.put(mavenProject, (Xml.Document) document);
@@ -760,10 +766,6 @@ private static List<Path> listJavaSources(Path sourceDirectory) throws MojoExecu
         return listSources(sourceDirectory, ".java");
     }
 
-    private static List<Path> listKotlinSources(Path sourceDirectory) throws MojoExecutionException {
-        return listSources(sourceDirectory, ".kt");
-    }
-
     private static List<Path> listSources(Path sourceDirectory, String extension) throws MojoExecutionException {
         if (!Files.exists(sourceDirectory)) {
             return emptyList();

src/test/java/org/openrewrite/maven/KotlinIT.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2020 the original author or authors.
+ * <p>
+ * 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
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.
+ */
+package org.openrewrite.maven;
+
+import com.soebes.itf.jupiter.extension.*;
+import com.soebes.itf.jupiter.maven.MavenExecutionResult;
+import org.junit.jupiter.api.condition.DisabledOnOs;
+import org.junit.jupiter.api.condition.OS;
+
+import static com.soebes.itf.extension.assertj.MavenITAssertions.assertThat;
+
+@MavenJupiterExtension
+@MavenOption(MavenCLIOptions.NO_TRANSFER_PROGRESS)
+@MavenOption(MavenCLIExtra.MUTE_PLUGIN_VALIDATION_WARNING)
+@MavenOption(MavenCLIOptions.VERBOSE)
+@DisabledOnOs(OS.WINDOWS)
+@MavenGoal("install")
+@MavenGoal("${project.groupId}:${project.artifactId}:${project.version}:run")
+class KotlinIT {
+    @MavenTest
+    void basic_kotlin_project(MavenExecutionResult result) {
+        assertThat(result)
+            .isSuccessful()
+            .out()
+            .debug()
+            .anySatisfy(line -> assertThat(line).contains("Scanned 1 kotlin source files in main scope."))
+            .anySatisfy(line -> assertThat(line).contains("org.openrewrite.kotlin.format.AutoFormat"));
+    }
+}

src/test/resources-its/org/openrewrite/maven/KotlinIT/basic_kotlin_project/pom.xml

@@ -0,0 +1,111 @@
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xmlns="http://maven.apache.org/POM/4.0.0"
+         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.openrewrite.maven</groupId>
+    <artifactId>basic_kotlin_project</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+    <name>KotlinIT#basic_kotlin_project</name>
+
+    <properties>
+        <kotlin.version>1.9.10</kotlin.version>
+        <jdk.version>17</jdk.version>
+        <java.version>${jdk.version}</java.version>
+        <maven.compiler.source>${jdk.version}</maven.compiler.source>
+        <maven.compiler.target>${jdk.version}</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.jetbrains.kotlin</groupId>
+                <artifactId>kotlin-maven-plugin</artifactId>
+                <version>${kotlin.version}</version>
+                <executions>
+                    <execution>
+                        <id>compile</id>
+                        <phase>process-sources</phase>
+                        <goals>
+                            <goal>compile</goal>
+                        </goals>
+                        <configuration>
+                            <sourceDirs>
+                                <sourceDir>${project.basedir}/src/main/java</sourceDir>
+                            </sourceDirs>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.13.0</version>
+                <configuration>
+                    <source>${java.version}</source>
+                    <target>${java.version}</target>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>default-compile</id>
+                        <phase>none</phase>
+                    </execution>
+                    <execution>
+                        <id>default-testCompile</id>
+                        <phase>none</phase>
+                    </execution>
+                    <execution>
+                        <id>java-compile</id>
+                        <phase>compile</phase>
+                        <goals>
+                            <goal>compile</goal>
+                        </goals>
+                    </execution>
+                    <execution>
+                        <id>java-test-compile</id>
+                        <phase>test-compile</phase>
+                        <goals>
+                            <goal>testCompile</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+
+            <plugin>
+                <groupId>@project.groupId@</groupId>
+                <artifactId>@project.artifactId@</artifactId>
+                <version>@project.version@</version>
+                <configuration>
+                    <activeRecipes>
+                        <recipe>org.openrewrite.kotlin.format.AutoFormat</recipe>
+                    </activeRecipes>
+                </configuration>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.openrewrite.recipe</groupId>
+                        <artifactId>rewrite-all</artifactId>
+                        <version>1.3.4</version>
+                    </dependency>
+                </dependencies>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-stdlib</artifactId>
+            <version>${kotlin.version}</version>
+        </dependency>
+    </dependencies>
+
+    <repositories>
+        <repository>
+            <id>mavenCentral</id>
+            <url>https://repo1.maven.org/maven2/</url>
+        </repository>
+    </repositories>
+</project>

src/test/resources-its/org/openrewrite/maven/KotlinIT/basic_kotlin_project/src/main/java/sample/MyClass.kt

@@ -0,0 +1,5 @@
+  package sample
+
+    class MyClass {
+
+       }