feat: Show basic information messages

Agent now prints "starting" and "appmap saved" messages on stdout
unless appmap.silent is set.

Author: dividedmind

agent/src/main/java/com/appland/appmap/Agent.java

@@ -17,6 +17,7 @@
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
+import com.appland.appmap.util.Logger;
 import org.apache.commons.io.FilenameUtils;
 import org.apache.commons.io.IOUtils;
 import org.tinylog.TaggedLogger;
@@ -66,8 +67,10 @@ public static void premain(String agentArgs, Instrumentation inst) {
           "To disable the automatic creation of this log file, set the system property {} to 'true'",
           Properties.DISABLE_LOG_FILE_KEY);
     }
+    String implementationVersion = Agent.class.getPackage().getImplementationVersion();
+    Logger.printUserMessage("AppMap agent version %s starting\n", implementationVersion);
     logger.info("Agent version {}, current time mills: {}",
-        Agent.class.getPackage().getImplementationVersion(), start);
+            implementationVersion, start);
     logger.info("config: {}", AppMapConfig.get());
     logger.info("System properties: {}", System.getProperties());
     logger.debug(new Exception(), "whereAmI");

agent/src/main/java/com/appland/appmap/config/Properties.java

@@ -9,6 +9,9 @@
 public class Properties {
   public static final String APPMAP_OUTPUT_DIRECTORY_KEY = "appmap.output.directory";
   public static final String DISABLE_LOG_FILE_KEY = "appmap.disableLogFile";
+
+  public static final Boolean Silent = resolveProperty("appmap.silent", false);
+
   public static final Boolean DisableLogFile = resolveProperty(DISABLE_LOG_FILE_KEY, true);
   public static final Boolean Debug = resolveProperty("appmap.debug", false);
   public static final Boolean DebugHooks = Debug || (System.getProperty("appmap.debug.hooks") != null);

agent/src/main/java/com/appland/appmap/record/Recording.java

@@ -18,6 +18,7 @@
 import java.util.List;
 import java.util.function.Function;
 
+import com.appland.appmap.util.Logger;
 import org.tinylog.TaggedLogger;
 
 import com.appland.appmap.config.AppMapConfig;
@@ -94,6 +95,7 @@ public Path moveTo(Path targetPath) {
             throw new RuntimeException(String.join(", ", errors));
         }
 
+        Logger.printUserMessage("AppMap recording saved to %s\n", targetPath.toAbsolutePath());
         return targetPath;
     }
 

agent/src/main/java/com/appland/appmap/util/Logger.java

@@ -1,6 +1,7 @@
 package com.appland.appmap.util;
 
 import com.appland.appmap.config.AppMapConfig;
+import com.appland.appmap.config.Properties;
 
 public class Logger {
   private static final org.tinylog.TaggedLogger logger = AppMapConfig.getLogger(null);
@@ -25,4 +26,15 @@ public static void error(Throwable t) {
     println(t);
   }
 
+  /**
+   * Print a message on stderr unless the silent flag is set.
+   * @param format
+   * @param args
+   */
+  public static void printUserMessage(String format, Object... args) {
+    if (!Properties.Silent) {
+      System.err.printf(format, args);
+    }
+  }
+
 }