CLIng: finish TODO (#1888)

Also clear up javadoc.

api/maven-api-cli/src/main/java/org/apache/maven/api/cli/mvn/forked/ForkedMavenInvoker.java

@@ -22,7 +22,7 @@ import org.apache.maven.api.annotations.Experimental;
 import org.apache.maven.api.cli.mvn.MavenInvoker;
 
 /**
- * Local Maven invoker.
+ * Forked Maven invoker.
  *
  * @since 4.0.0
  */

api/maven-api-cli/src/main/java/org/apache/maven/api/cli/mvn/local/LocalMavenInvoker.java

@@ -24,7 +24,7 @@ import org.apache.maven.api.cli.mvn.MavenInvokerRequest;
 import org.apache.maven.api.cli.mvn.MavenOptions;
 
 /**
- * Local Maven invoker.
+ * Local Maven invoker, it expects all the Maven be present in classpath.
  *
  * @since 4.0.0
  */

api/maven-api-cli/src/main/java/org/apache/maven/api/cli/mvn/resident/ResidentMavenInvoker.java

@@ -25,7 +25,7 @@ import org.apache.maven.api.cli.mvn.MavenInvokerRequest;
 import org.apache.maven.api.cli.mvn.MavenOptions;
 
 /**
- * Resident invoker. Instance is shut down when this instance is closed.
+ * Resident Maven invoker, similar to local. Instance is shut down when this instance is closed.
  *
  * @since 4.0.0
  */

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvn/forked/DefaultForkedMavenParser.java

@@ -18,8 +18,13 @@
  */
 package org.apache.maven.cling.invoker.mvn.forked;
 
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.Arrays;
 import java.util.List;
+import java.util.stream.Collectors;
 
 import org.apache.commons.cli.ParseException;
 import org.apache.maven.api.cli.ParserException;
@@ -30,6 +35,9 @@ import org.apache.maven.cling.invoker.mvn.BaseMavenParser;
 import org.apache.maven.cling.invoker.mvn.CommonsCliMavenOptions;
 import org.apache.maven.cling.invoker.mvn.LayeredMavenOptions;
 
+/**
+ * Forked invoker that invokes Maven in a child process.
+ */
 public class DefaultForkedMavenParser extends BaseMavenParser<MavenOptions, ForkedMavenInvokerRequest>
         implements ForkedMavenParser {
 
@@ -55,8 +63,17 @@ public class DefaultForkedMavenParser extends BaseMavenParser<MavenOptions, Fork
 
     protected List<String> getJvmArguments(Path rootDirectory) {
         if (rootDirectory != null) {
-            // TODO: do this
+            Path jvmConfig = rootDirectory.resolve(".mvn/jvm.config");
-            return null;
+            if (Files.exists(jvmConfig)) {
+                try {
+                    return Files.readAllLines(jvmConfig).stream()
+                            .filter(l -> !l.isBlank() && !l.startsWith("#"))
+                            .flatMap(l -> Arrays.stream(l.split(" ")))
+                            .collect(Collectors.toList());
+                } catch (IOException e) {
+                    throw new UncheckedIOException(e);
+                }
+            }
         }
         return null;
     }

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvn/local/DefaultLocalMavenInvoker.java

@@ -24,6 +24,12 @@ import org.apache.maven.api.cli.mvn.local.LocalMavenInvoker;
 import org.apache.maven.cling.invoker.ProtoLookup;
 import org.apache.maven.cling.invoker.mvn.DefaultMavenInvoker;
 
+/**
+ * Local invoker implementation, when Maven CLI is being run. System uses ClassWorld launcher, and class world
+ * instance is passed in via "enhanced" main method. Hence, this class expects fully setup ClassWorld via constructor.
+ *
+ * @see org.apache.maven.cling.MavenCling
+ */
 public class DefaultLocalMavenInvoker
         extends DefaultMavenInvoker<
                 MavenOptions, MavenInvokerRequest<MavenOptions>, DefaultLocalMavenInvoker.LocalContext>

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvn/resident/DefaultResidentMavenInvoker.java

@@ -29,8 +29,9 @@ import org.apache.maven.cling.invoker.ProtoLookup;
 import org.apache.maven.cling.invoker.mvn.DefaultMavenInvoker;
 
 /**
- * Local invoker implementation, when Maven CLI is being run. System uses ClassWorld launcher, and class world
+ * Local resident invoker implementation, similar to "local" but keeps Maven instance resident. This implies, that
- * instance is passed in via "enhanced" main method. Hence, this class expects fully setup ClassWorld via constructor.
+ * things like environment, system properties, extensions etc. are loaded only once. It is caller duty to ensure
+ * that subsequent call is right for the resident instance (ie no env change or different extension needed).
  */
 public class DefaultResidentMavenInvoker
         extends DefaultMavenInvoker<