[MNG-8512] Fix org.slf4j.simpleLogger.defaultLogLevel Configuration conflict

impl/maven-cli/src/main/java/org/apache/maven/cling/logging/impl/MavenSimpleConfiguration.java

@@ -20,7 +20,9 @@
 
 import org.apache.maven.cling.logging.BaseSlf4jConfiguration;
 import org.apache.maven.slf4j.MavenLoggerFactory;
+import org.apache.maven.slf4j.MavenSimpleLogger;
 import org.slf4j.ILoggerFactory;
+import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
@@ -29,6 +31,8 @@
  * @since 3.1.0
  */
 public class MavenSimpleConfiguration extends BaseSlf4jConfiguration {
+    private static final Logger LOGGER = LoggerFactory.getLogger(MavenSimpleConfiguration.class);
+
     @Override
     public void setRootLoggerLevel(Level level) {
         String value =
@@ -37,7 +41,14 @@ public void setRootLoggerLevel(Level level) {
                     case INFO -> "info";
                     default -> "error";
                 };
-        System.setProperty("org.slf4j.simpleLogger.defaultLogLevel", value);
+
+        String current = System.setProperty(MavenSimpleLogger.DEFAULT_LOG_LEVEL_KEY, value);
+        if (current != null && !value.equalsIgnoreCase(current)) {
+            LOGGER.info(
+                    "System property '" + MavenSimpleLogger.DEFAULT_LOG_LEVEL_KEY + "' is already set to '" + current
+                            + "' - ignoring system property and get log level from -X/-e/-q options, log level will be set to"
+                            + value);
+        }
     }
 
     @Override

impl/maven-logging/src/main/java/org/apache/maven/slf4j/MavenLoggerFactory.java

@@ -21,13 +21,14 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
+import org.apache.maven.logging.api.LogLevelRecorder;
 import org.slf4j.ILoggerFactory;
 import org.slf4j.Logger;
 
 /**
  * LogFactory for Maven which can create a simple logger or one which, if set, fails the build on a severity threshold.
  */
-public class MavenLoggerFactory implements org.apache.maven.logging.api.LogLevelRecorder, ILoggerFactory {
+public class MavenLoggerFactory implements LogLevelRecorder, ILoggerFactory {
     final DefaultLogLevelRecorder logLevelRecorder = new DefaultLogLevelRecorder();
     final ConcurrentMap<String, Logger> loggerMap = new ConcurrentHashMap<>();
 

impl/maven-logging/src/main/java/org/apache/maven/slf4j/MavenSimpleLogger.java

@@ -41,6 +41,8 @@ public class MavenSimpleLogger extends MavenBaseLogger {
 
     static Consumer<String> logSink;
 
+    public static final String DEFAULT_LOG_LEVEL_KEY = "org.slf4j.simpleLogger.defaultLogLevel";
+
     public static void setLogSink(Consumer<String> logSink) {
         MavenSimpleLogger.logSink = logSink;
     }