Debugger Restart Frame

src/org/rascalmpl/dap/RascalDebugAdapter.java

@@ -156,7 +156,7 @@ public CompletableFuture<Capabilities> initialize(InitializeRequestArguments arg
 
             capabilities.setSupportsConfigurationDoneRequest(true);
             capabilities.setSupportsStepBack(false);
-            capabilities.setSupportsRestartFrame(false);
+            capabilities.setSupportsRestartFrame(true);
             capabilities.setSupportsSetVariable(false);
             capabilities.setSupportsRestartRequest(false);
             capabilities.setSupportsCompletionsRequest(true);
@@ -395,13 +395,15 @@ private StackFrame createStackFrame(int id, ISourceLocation loc, String name){
         StackFrame frame = new StackFrame();
         frame.setId(id);
         frame.setName(name);
+        frame.setCanRestart(false);
         if(loc != null && !loc.getScheme().equals(promptLocation.getScheme())) {
             var offsets = columns.get(loc);
             var line = shiftLine(loc.getBeginLine());
             var column = shiftColumn(offsets.translateColumn(loc.getBeginLine(), loc.getBeginColumn(), false));
             frame.setLine(line);
             frame.setColumn(column);
             frame.setSource(getSourceFromISourceLocation(loc));
+            frame.setCanRestart(true);
         }
         return frame;
     }
@@ -766,6 +768,23 @@ public CompletableFuture<CompletionsResponse> completions(CompletionsArguments a
             return response;
         }, ownExecutor);
 	}
-
+
+    @Override
+    public CompletableFuture<Void> restartFrame(RestartFrameArguments args) {
+        return CompletableFuture.supplyAsync(() -> {
+            if(args.getFrameId() == 0){ 
+                // From DAP spec, we must send a stopped event. Here we use this to indicate that the REPL frame cannot be restarted
+                StoppedEventArguments stoppedEventArguments = new StoppedEventArguments();
+                stoppedEventArguments.setThreadId(RascalDebugAdapter.mainThreadID);
+                stoppedEventArguments.setDescription("Cannot restart the REPL frame");
+                stoppedEventArguments.setReason("restart");
+                client.stopped(stoppedEventArguments);
+            } else{
+                debugHandler.processMessage(DebugMessageFactory.requestRestartFrame(args.getFrameId()));
+            }
+            return null;
+
+        }, ownExecutor);
+    }
 }
 

src/org/rascalmpl/dap/RascalDebugEventTrigger.java

@@ -145,6 +145,17 @@ public void fireSuspendByExceptionEvent(Exception exception) {
         client.stopped(stoppedEventArguments);
     }
 
+    @Override
+    public void fireSuspendByRestartFrameEndEvent() {
+        suspendedState.suspended();
+
+        StoppedEventArguments stoppedEventArguments = new StoppedEventArguments();
+        stoppedEventArguments.setThreadId(RascalDebugAdapter.mainThreadID);
+        stoppedEventArguments.setDescription("Paused after restarting frame.");
+        stoppedEventArguments.setReason("restart");
+        client.stopped(stoppedEventArguments);
+    }
+
     @Override
     public void fireSuspendEvent(RascalEvent.Detail detail) {}
 }

src/org/rascalmpl/debug/AbstractInterpreterEventTrigger.java

@@ -127,6 +127,14 @@ public void fireSuspendByStepEndEvent() {
 		fireSuspendEvent(RascalEvent.Detail.STEP_END);
 	}
 
+	/**
+	 * Fires a resume event for this debug element with detail
+	 * <code>RascalEvent.Detail.CLIENT_REQUEST</code>.
+	 */
+	public void fireSuspendByRestartFrameEndEvent() {
+		fireSuspendEvent(RascalEvent.Detail.RESTART_FRAME_END);
+	}
+
 	/**
 	 * Fires a suspend event for this debug element with detail
 	 * <code>RascalEvent.Detail.STEP_END</code>.

src/org/rascalmpl/debug/DebugHandler.java

@@ -18,6 +18,8 @@
 
 import static org.rascalmpl.debug.AbstractInterpreterEventTrigger.newNullEventTrigger;
 
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.Map;
 import java.util.function.IntSupplier;
 
@@ -26,6 +28,7 @@
 import org.rascalmpl.interpreter.Evaluator;
 import org.rascalmpl.interpreter.control_exceptions.InterruptException;
 import org.rascalmpl.interpreter.control_exceptions.QuitException;
+import org.rascalmpl.interpreter.control_exceptions.RestartFrameException;
 import org.rascalmpl.interpreter.env.Environment;
 import org.rascalmpl.interpreter.env.Pair;
 import org.rascalmpl.interpreter.result.Result;
@@ -107,6 +110,12 @@ private enum DebugStepMode {
 	 */
 	private Evaluator evaluator = null;
 
+	/**
+	 * Flag indicating a frame restart has been requested.
+	 * Set by the debugger thread, checked and used by the evaluated thread in suspended().
+	 */
+	private AtomicInteger restartFrameId = new AtomicInteger(-1);
+
 	/**
 	 * Create a new debug handler with its own interpreter event trigger.
 	 */
@@ -276,6 +285,12 @@ public void suspended(Object runtime, IntSupplier getCallStackSize, AbstractAST
 	            // Ignore
 	        }
 	    }
+
+	    // Check if a frame restart was requested while suspended
+		int frameToRestart = restartFrameId.getAndSet(-1);
+	    if (frameToRestart >= 0) {
+	        throw new RestartFrameException(frameToRestart);
+	    }
 	}
 
 	private boolean handleExceptionSuspension(Evaluator eval, Exception e) {
@@ -487,6 +502,19 @@ public void processMessage(IDebugMessage message) {
 	        terminateAction.run();
 	      }
 	      break;
+
+		case RESTART_FRAME:
+			if(suspended) {
+				int frameId = (int) message.getPayload();
+				assert frameId >= 0 && frameId < evaluator.getCurrentStack().size(): "Frame id out of bounds: " + frameId;
+				// Set flag for the evaluated thread to handle the restart
+				if (restartFrameId.compareAndSet(-1, frameId)) {
+					// Unsuspend to let the evaluated thread continue and hit the restart exception
+					setSuspendRequested(true);
+					setSuspended(false);
+				}
+			}
+		  break;
 		}
 	    break;
 	  }

src/org/rascalmpl/debug/DebugMessageFactory.java

@@ -46,6 +46,10 @@ public static IDebugMessage requestStepOut(){
 	public static IDebugMessage requestTermination() {
 		return new DebugMessage(IDebugMessage.Action.TERMINATE, IDebugMessage.Subject.INTERPRETER, IDebugMessage.Detail.UNKNOWN);
 	}
+
+	public static IDebugMessage requestRestartFrame(int frameId) {
+		return new DebugMessage(IDebugMessage.Action.RESTART_FRAME, IDebugMessage.Subject.INTERPRETER, IDebugMessage.Detail.UNKNOWN, frameId);
+	}
 
 	/*
 	 * Breakpoint requests.

src/org/rascalmpl/debug/IDebugMessage.java

@@ -22,7 +22,7 @@ public interface IDebugMessage {
 	 * <code>UNKNOWN</code> if not provided.
 	 */
 	enum Action {
-		UNKNOWN, SET, DELETE, TERMINATE, SUSPEND, RESUME
+		UNKNOWN, SET, DELETE, TERMINATE, SUSPEND, RESUME, RESTART_FRAME
 	}
 
 	/**

src/org/rascalmpl/debug/RascalEvent.java

@@ -31,7 +31,7 @@ public enum Kind {
 	 * Details additional to {@link Kind}.
 	 */
 	public enum Detail {
-		UNSPECIFIED, CLIENT_REQUEST, STEP_INTO, STEP_OVER, STEP_END, BREAKPOINT, STEP_OUT, EXCEPTION
+		UNSPECIFIED, CLIENT_REQUEST, STEP_INTO, STEP_OVER, STEP_END, BREAKPOINT, STEP_OUT, EXCEPTION, RESTART_FRAME_END
 	}
 
 	private final Kind kind;

src/org/rascalmpl/interpreter/Evaluator.java

@@ -1608,12 +1608,15 @@ public void notifyAboutSuspension(AbstractAST currentAST) {
     @Override
     public void notifyAboutSuspensionException(Exception t) {
         currentException = t;
-        if (!suspendTriggerListeners.isEmpty()) { // remove the breakable condition since exception can happen anywhere
-            for (IRascalSuspendTriggerListener listener : suspendTriggerListeners) {
-                listener.suspended(this, () -> getCallStack().size(), currentAST);
+        try{
+            if (!suspendTriggerListeners.isEmpty()) { // remove the breakable condition since exception can happen anywhere
+                for (IRascalSuspendTriggerListener listener : suspendTriggerListeners) {
+                    listener.suspended(this, () -> getCallStack().size(), currentAST);
+                }
             }
+        } finally { // clear the exception after notifying listeners
+            currentException = null;
         }
-        currentException = null;
     }
 
     public AbstractInterpreterEventTrigger getEventTrigger() {

src/org/rascalmpl/interpreter/control_exceptions/RestartFrameException.java

@@ -0,0 +1,20 @@
+package org.rascalmpl.interpreter.control_exceptions;
+
+/**
+ * Exception thrown to request a frame restart in the debugger.
+ * This exception carries the target frame ID and propagates up the call stack
+ * until it reaches the appropriate frame that should be restarted.
+ */
+public class RestartFrameException extends ControlException {
+	private final static long serialVersionUID = 1L;
+	private final int targetFrameId;
+
+	public RestartFrameException(int targetFrameId) {
+		super("Restart frame: " + targetFrameId);
+		this.targetFrameId = targetFrameId;
+	}
+
+	public int getTargetFrameId() {
+		return targetFrameId;
+	}
+}