Support debug protocol.

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/adapter/DebugAdapter.java

@@ -27,6 +27,7 @@
 import com.microsoft.java.debug.core.adapter.handler.HotCodeReplaceHandler;
 import com.microsoft.java.debug.core.adapter.handler.InitializeRequestHandler;
 import com.microsoft.java.debug.core.adapter.handler.LaunchRequestHandler;
+import com.microsoft.java.debug.core.adapter.handler.RestartFrameHandler;
 import com.microsoft.java.debug.core.adapter.handler.ScopesRequestHandler;
 import com.microsoft.java.debug.core.adapter.handler.SetBreakpointsRequestHandler;
 import com.microsoft.java.debug.core.adapter.handler.SetExceptionBreakpointsRequestHandler;
@@ -106,6 +107,7 @@ private void initialize() {
         registerHandler(new SetVariableRequestHandler());
         registerHandler(new EvaluateRequestHandler());
         registerHandler(new HotCodeReplaceHandler());
+        registerHandler(new RestartFrameHandler());
     }
 
     private void registerHandler(IDebugRequestHandler handler) {

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/adapter/ErrorCode.java

@@ -29,7 +29,8 @@ public enum ErrorCode {
     INVALID_ENCODING(1012),
     VM_TERMINATED(1013),
     LAUNCH_IN_TERMINAL_FAILURE(1014),
-    STEP_FAILURE(1015);
+    STEP_FAILURE(1015),
+    RESTARTFRAME_FAILURE(1016);
 
     private int id;
 

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/adapter/handler/InitializeRequestHandler.java

@@ -50,6 +50,7 @@ public CompletableFuture<Messages.Response> handle(Requests.Command command, Req
         caps.supportsConditionalBreakpoints = true;
         caps.supportsSetVariable = true;
         caps.supportTerminateDebuggee = true;
+        caps.supportsRestartFrame = true;
         Types.ExceptionBreakpointFilter[] exceptionFilters = {
             Types.ExceptionBreakpointFilter.UNCAUGHT_EXCEPTION_FILTER,
             Types.ExceptionBreakpointFilter.CAUGHT_EXCEPTION_FILTER,

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/adapter/handler/RestartFrameHandler.java

@@ -0,0 +1,111 @@
+/*******************************************************************************
+* Copyright (c) 2017 Microsoft Corporation and others.
+* All rights reserved. This program and the accompanying materials
+* are made available under the terms of the Eclipse Public License v1.0
+* which accompanies this distribution, and is available at
+* http://www.eclipse.org/legal/epl-v10.html
+*
+* Contributors:
+*     Microsoft Corporation - initial API and implementation
+*******************************************************************************/
+
+package com.microsoft.java.debug.core.adapter.handler;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+
+import com.microsoft.java.debug.core.DebugException;
+import com.microsoft.java.debug.core.DebugUtility;
+import com.microsoft.java.debug.core.StackFrameUtility;
+import com.microsoft.java.debug.core.adapter.AdapterUtils;
+import com.microsoft.java.debug.core.adapter.ErrorCode;
+import com.microsoft.java.debug.core.adapter.IDebugAdapterContext;
+import com.microsoft.java.debug.core.adapter.IDebugRequestHandler;
+import com.microsoft.java.debug.core.adapter.variables.StackFrameReference;
+import com.microsoft.java.debug.core.protocol.Events;
+import com.microsoft.java.debug.core.protocol.Events.UserNotificationEvent.NotificationType;
+import com.microsoft.java.debug.core.protocol.Messages.Response;
+import com.microsoft.java.debug.core.protocol.Requests;
+import com.microsoft.java.debug.core.protocol.Requests.Arguments;
+import com.microsoft.java.debug.core.protocol.Requests.Command;
+import com.microsoft.java.debug.core.protocol.Requests.RestartFrameArguments;
+import com.sun.jdi.StackFrame;
+import com.sun.jdi.ThreadReference;
+import com.sun.jdi.request.StepRequest;
+
+/**
+ * Support Eclipse's `Drop To Frame` action, which is restartFrame in VSCode's
+ * debug.
+ */
+public class RestartFrameHandler implements IDebugRequestHandler {
+
+    @Override
+    public List<Command> getTargetCommands() {
+        return Arrays.asList(Requests.Command.RESTARTFRAME);
+    }
+
+    @Override
+    public CompletableFuture<Response> handle(Command command, Arguments arguments, Response response, IDebugAdapterContext context) {
+        RestartFrameArguments restartFrameArgs = (RestartFrameArguments) arguments;
+        StackFrameReference stackFrameReference = (StackFrameReference) context.getRecyclableIdPool().getObjectById(restartFrameArgs.frameId);
+
+        if (stackFrameReference == null) {
+            return AdapterUtils.createAsyncErrorResponse(response, ErrorCode.RESTARTFRAME_FAILURE,
+                    String.format("RestartFrame: cannot find the stack frame with frameID %s", restartFrameArgs.frameId));
+        }
+
+        if (canRestartFrame(context, stackFrameReference)) {
+            try {
+                ThreadReference reference = stackFrameReference.getThread();
+                popStackFrames(context, reference, stackFrameReference.getDepth());
+                stepInto(context, reference);
+            } catch (DebugException de) {
+                context.getProtocolServer().sendEvent(new Events.UserNotificationEvent(NotificationType.ERROR, de.getMessage()));
+            }
+            return CompletableFuture.completedFuture(response);
+        } else {
+            context.getProtocolServer().sendEvent(new Events.UserNotificationEvent(NotificationType.ERROR, "Current stack frame doesn't support restart."));
+            context.getProtocolServer().sendEvent(new Events.StoppedEvent("restartframe", stackFrameReference.getThread().uniqueID()));
+            return AdapterUtils.createAsyncErrorResponse(response, ErrorCode.RESTARTFRAME_FAILURE, "Failed to restart the selected stack frame.");
+        }
+    }
+
+    private boolean canRestartFrame(IDebugAdapterContext context, StackFrameReference frameReference) {
+        if (!context.getDebugSession().getVM().canPopFrames()) {
+            return false;
+        }
+        ThreadReference reference = frameReference.getThread();
+        StackFrame[] frames = context.getStackFrameManager().reloadStackFrames(reference);
+
+        // The frame cannot be the bottom one of the call stack:
+        if (frames.length <= frameReference.getDepth() + 1) {
+            return false;
+        }
+
+        // Cannot restart frame involved with native call stacks:
+        for (int i = 0; i <= frameReference.getDepth() + 1; i++) {
+            if (StackFrameUtility.isNative(frames[i])) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private void popStackFrames(IDebugAdapterContext context, ThreadReference thread, int depth) throws DebugException {
+        StackFrame[] frames = context.getStackFrameManager().reloadStackFrames(thread);
+        StackFrameUtility.pop(frames[depth]);
+    }
+
+    private void stepInto(IDebugAdapterContext context, ThreadReference thread) {
+        StepRequest request = DebugUtility.createStepIntoRequest(thread, context.getStepFilters().classNameFilters);
+        context.getDebugSession().getEventHub().stepEvents().filter(debugEvent -> request.equals(debugEvent.event.request())).take(1).subscribe(debugEvent -> {
+            debugEvent.shouldResume = false;
+            // Have to send two events to keep the UI sync with the step in operations:
+            context.getProtocolServer().sendEvent(new Events.StoppedEvent("step", thread.uniqueID()));
+            context.getProtocolServer().sendEvent(new Events.ContinuedEvent(thread.uniqueID()));
+        });
+        request.enable();
+        thread.resume();
+    }
+}

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/protocol/Requests.java

@@ -259,6 +259,10 @@ public static class RedefineClassesArguments extends Arguments {
 
     }
 
+    public static class RestartFrameArguments extends Arguments {
+        public int frameId;
+    }
+
     public static enum Command {
         INITIALIZE("initialize", InitializeArguments.class),
         LAUNCH("launch", LaunchArguments.class),
@@ -271,6 +275,7 @@ public static enum Command {
         STEPOUT("stepOut", StepOutArguments.class),
         PAUSE("pause", PauseArguments.class),
         STACKTRACE("stackTrace", StackTraceArguments.class),
+        RESTARTFRAME("restartFrame", RestartFrameArguments.class),
         SCOPES("scopes", ScopesArguments.class),
         VARIABLES("variables", VariablesArguments.class),
         SETVARIABLE("setVariable", SetVariableArguments.class),

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/protocol/Types.java

@@ -215,6 +215,7 @@ public static class Capabilities {
         public boolean supportsHitConditionalBreakpoints;
         public boolean supportsConditionalBreakpoints;
         public boolean supportsEvaluateForHovers;
+        public boolean supportsRestartFrame;
         public boolean supportsSetVariable;
         public boolean supportsRestartRequest;
         public boolean supportTerminateDebuggee;