- Enabled incremental Kotlin compilationboth build configuration and KotlinCompilationProvider.

- Adjusted JVM options to add module opens for compatibility and reordered existing JVM settings for better clarity
- Added (commented) compiler flags to consider

Author: kpavlov

.mvn/jvm.config

@@ -1,4 +1,6 @@
--Dmaven.wagon.httpconnectionManager.ttlSeconds=120
--Dmaven.wagon.http.retryHandler.requestSentEnabled=true
+--add-opens=java.base/java.io=ALL-UNNAMED
+--add-opens=java.base/java.lang=ALL-UNNAMED
 -Dmaven.wagon.http.retryHandler.count=10
--Xmx5g
+-Dmaven.wagon.http.retryHandler.requestSentEnabled=true
+-Dmaven.wagon.httpconnectionManager.ttlSeconds=120
+-Xmx5g

build-parent/pom.xml

@@ -20,11 +20,12 @@
 
         <!-- These properties are needed in order for them to be resolvable by the generated projects -->
         <compiler-plugin.version>${version.compiler.plugin}</compiler-plugin.version>
+        <kotlin.compiler.incremental>true</kotlin.compiler.incremental>
         <kotlin.version>2.1.21</kotlin.version>
         <dokka.version>2.0.0</dokka.version>
         <scala.version>2.13.12</scala.version>
         <scala-maven-plugin.version>4.9.5</scala-maven-plugin.version>
-        <!-- not pretty but this is used in the codestarts and we don't want to break compatibility -->
+        <!-- not pretty, but this is used in the codestarts and we don't want to break compatibility -->
         <scala-plugin.version>${scala-maven-plugin.version}</scala-plugin.version>
         <jboss-bridger-plugin.version>1.6.Final</jboss-bridger-plugin.version>
 
@@ -601,6 +602,8 @@
                     <configuration>
                         <javaParameters>true</javaParameters>
                         <jvmTarget>${maven.compiler.release}</jvmTarget>
+                        <languageVersion>2.1</languageVersion>
+                        <apiVersion>2.1</apiVersion>
                     </configuration>
                 </plugin>
                 <plugin>

extensions/kotlin/deployment/src/main/java/io/quarkus/kotlin/deployment/KotlinCompilationProvider.java

@@ -1,12 +1,7 @@
 package io.quarkus.kotlin.deployment;
 
 import java.io.File;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.List;
-import java.util.Set;
-import java.util.StringJoiner;
+import java.util.*;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -48,6 +43,17 @@ public void compile(Set<File> filesToCompile, Context context) {
         compilerArguments.setJavaParameters(true);
         compilerArguments.setSuppressWarnings(true);
 
+        compilerArguments.setIncrementalCompilation(true);
+
+        // use javac or koltinc to compile java
+        // compilerArguments.setUseJavac(true); // Kotlinc can compile java sources too
+        // compilerArguments.setCompileJava(true);
+
+        // optional
+        // compilerArguments.setNoReflect(true); // be careful
+        // compilerArguments.setNoOptimize(true); // safe for hot reload/dev mode
+        // compilerArguments.setUseFastJarFileSystem(true);
+
         if (context.getCompilePluginArtifacts() != null && !context.getCompilePluginArtifacts().isEmpty()) {
             compilerArguments.setPluginClasspaths(context.getCompilePluginArtifacts().toArray(new String[0]));
         }
@@ -68,6 +74,7 @@ public void compile(Set<File> filesToCompile, Context context) {
                 final String key = matcher.group(2);
                 final String value = matcher.group(3);
                 sanitizedOptions.add("plugin:" + pluginId + ":" + key + "=" + value);
+                log.error("Sanitized option: " + sanitizedOptions);
                 compilerArguments.setPluginOptions(sanitizedOptions.toArray(new String[0]));
             }
         }