Use the same file traversal here that we generally use elsewhere.

This doesn't impose an arbitrary limit on how deeply nested sources can be.

pom.xml

@@ -4,7 +4,7 @@
 
     <groupId>org.openrewrite.maven</groupId>
     <artifactId>rewrite-maven-plugin</artifactId>
-    <version>5.44.0-SNAPSHOT</version>
+    <version>5.43.1-SNAPSHOT</version>
     <packaging>maven-plugin</packaging>
 
     <name>rewrite-maven-plugin</name>
@@ -62,8 +62,8 @@
 
     <properties>
         <!-- Pinned versions, as RELEASE would make it into the published pom.xml -->
-        <rewrite.version>8.39.0-SNAPSHOT</rewrite.version>
-        <rewrite.kotlin.version>1.22.0-SNAPSHOT</rewrite.kotlin.version>
+        <rewrite.version>8.38.0</rewrite.version>
+        <rewrite.kotlin.version>1.21.2</rewrite.kotlin.version>
 
         <!-- using 'ssh' url scheme by default, which assumes a human is performing git operations leveraging an ssh key -->
         <developerConnectionUrl>scm:git:ssh://[email protected]/openrewrite/rewrite-maven-plugin.git

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

@@ -56,10 +56,8 @@
 import java.io.File;
 import java.io.IOException;
 import java.nio.charset.Charset;
-import java.nio.file.Files;
-import java.nio.file.Path;
-import java.nio.file.PathMatcher;
-import java.nio.file.Paths;
+import java.nio.file.*;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.util.*;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Function;
@@ -763,9 +761,18 @@ private static List<Path> listSources(Path sourceDirectory, String extension) th
         if (!Files.exists(sourceDirectory)) {
             return emptyList();
         }
-
-        try (Stream<Path> files = Files.find(sourceDirectory, 16, (f, a) -> !a.isDirectory() && f.toString().endsWith(extension))) {
-            return files.collect(toList());
+        try {
+            List<Path> result = new ArrayList<>();
+            Files.walkFileTree(sourceDirectory, new SimpleFileVisitor<Path>() {
+                @Override
+                public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) {
+                    if (file.toString().endsWith(extension)) {
+                        result.add(file);
+                    }
+                    return FileVisitResult.CONTINUE;
+                }
+            });
+            return result;
         } catch (IOException e) {
             throw new MojoExecutionException("Unable to list source files of " + extension, e);
         }