fix: add validation for using packages or lockFilePath, update MISSING_DEPENDENCY_CONFIGURATION_ERROR message

Author: ih0r-d

graalpy-maven-plugin/src/main/java/org/graalvm/python/maven/plugin/LockPackagesMojo.java

@@ -82,7 +82,7 @@ public class LockPackagesMojo extends AbstractGraalPyMojo {
                   </configuration>
                 </plugin>
             
-              Option 2: Use a pip-compatible requirements file:
+              Option 2: Use a pip-compatible requirements.txt file:
             
                 <plugin>
                   <groupId>org.graalvm.python</groupId>
@@ -93,12 +93,16 @@ public class LockPackagesMojo extends AbstractGraalPyMojo {
                   </configuration>
                 </plugin>
             
-            NOTE:
-              • The <configuration> section must be declared on the graalpy-maven-plugin itself,
-                not inside the process-graalpy-resources execution goal.
+            IMPORTANT:
+              • The requirementsFile workflow follows pip's native behavior.
+              • GraalPy lock files are NOT used or generated when requirementsFile is specified.
+              • The 'lock-packages' goal is NOT supported with <requirementsFile>.
+              • Users are expected to manage locking / freezing themselves using pip conventions (e.g., pip freeze).
               • Do not define both <packages> and <requirementsFile> at the same time.
+              • The <configuration> section must be declared on the graalpy-maven-plugin itself,
+                not inside a specific execution.
             
-            For more information, please refer to:
+            For more details, see:
             https://github.com/oracle/graalpython/blob/master/docs/user/Embedding-Build-Tools.md
             """;
 

org.graalvm.python.embedding.tools/src/main/java/org/graalvm/python/embedding/tools/vfs/VFSUtils.java

@@ -578,6 +578,7 @@ static void installPackages(Path venvDirectory, List<String> packages, Path lock
         Objects.requireNonNull(packages);
         log.info("Using inline <packages> dependency mode.");
 
+        validatePackagesOrLockFile(packages, lockFilePath);
         logVenvArgs(venvDirectory, packages, lockFilePath, launcher, graalPyVersion, log);
 
         List<String> pluginPackages = trim(packages);
@@ -683,7 +684,19 @@ public static void lockPackages(Path venvDirectory, List<String> packages, Path
 		}
 	}
 
-	private static void logVenvArgs(Path venvDirectory, List<String> packages, Path lockFile, Launcher launcherArgs,
+    private static void validatePackagesOrLockFile(List<String> packages, Path lockFilePath) {
+        boolean hasPackages = packages != null && !packages.isEmpty();
+        boolean hasLockFile = lockFilePath != null;
+
+        if (hasPackages == hasLockFile) {
+            throw new IllegalArgumentException(
+                    "Invalid configuration: <packages> and lock-file cannot be used together. Provide exactly one."
+            );
+        }
+    }
+
+
+    private static void logVenvArgs(Path venvDirectory, List<String> packages, Path lockFile, Launcher launcherArgs,
 			String graalPyVersion, BuildToolLog log) throws IOException {
 		if (log.isDebugEnabled()) {
 			// avoid computing classpath if not necessary