src,lib: minor --debug-brk cleanup

Minor cleanup of how --debug-brk works:
* We no longer need to use command line flags to expose the debug
  object.
* Do not depend on the existence of global.v8debug as a mechanism to
  determine if --debug-brk was specified.
* We no longer need to set a dummy listener with --debug-brk.

PR-URL: https://github.com/nodejs/node/pull/6599
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: cjihrig - Colin Ihrig <cjihrig@gmail.com>

lib/internal/bootstrap_node.js

@@ -136,7 +136,7 @@
 
         preloadModules();
 
-        if (global.v8debug &&
+        if (process._debugWaitConnect &&
             process.execArgv.some(function(arg) {
               return arg.match(/^--debug-brk(=[0-9]*)?$/);
             })) {
@@ -149,7 +149,7 @@
           // breakpoint message on line 1.
           //
           // A better fix would be to somehow get a message from the
-          // global.v8debug object about a connection, and runMain when
+          // V8 debug object about a connection, and runMain when
           // that occurs.  --isaacs
 
           var debugTimeout = +process.env.NODE_DEBUG_TIMEOUT || 50;

lib/module.js

@@ -4,7 +4,7 @@ const NativeModule = require('native_module');
 const util = require('util');
 const internalModule = require('internal/module');
 const internalUtil = require('internal/util');
-const runInThisContext = require('vm').runInThisContext;
+const vm = require('vm');
 const assert = require('assert').ok;
 const fs = require('fs');
 const path = require('path');
@@ -508,13 +508,13 @@ Module.prototype._compile = function(content, filename) {
   // create wrapper function
   var wrapper = Module.wrap(content);
 
-  var compiledWrapper = runInThisContext(wrapper, {
+  var compiledWrapper = vm.runInThisContext(wrapper, {
     filename: filename,
     lineOffset: 0,
     displayErrors: true
   });
 
-  if (global.v8debug) {
+  if (process._debugWaitConnect) {
     if (!resolvedArgv) {
       // we enter the repl if we're not given a filename argument.
       if (process.argv[1]) {
@@ -526,11 +526,9 @@ Module.prototype._compile = function(content, filename) {
 
     // Set breakpoint on module start
     if (filename === resolvedArgv) {
-      // Installing this dummy debug event listener tells V8 to start
-      // the debugger.  Without it, the setBreakPoint() fails with an
-      // 'illegal access' error.
-      global.v8debug.Debug.setListener(function() {});
-      global.v8debug.Debug.setBreakPoint(compiledWrapper, 0, 0);
+      delete process._debugWaitConnect;
+      const Debug = vm.runInDebugContext('Debug');
+      Debug.setBreakPoint(compiledWrapper, 0, 0);
     }
   }
   var dirname = path.dirname(filename);

src/node.cc

@@ -3179,6 +3179,11 @@ void SetupProcessObject(Environment* env,
     READONLY_PROPERTY(process, "traceDeprecation", True(env->isolate()));
   }
 
+  // --debug-brk
+  if (debug_wait_connect) {
+    READONLY_PROPERTY(process, "_debugWaitConnect", True(env->isolate()));
+  }
+
   // --security-revert flags
 #define V(code, _, __)                                                        \
   do {                                                                        \
@@ -4087,11 +4092,6 @@ void Init(int* argc,
     exit(9);
   }
 
-  if (debug_wait_connect) {
-    const char expose_debug_as[] = "--expose_debug_as=v8debug";
-    V8::SetFlagsFromString(expose_debug_as, sizeof(expose_debug_as) - 1);
-  }
-
   // Unconditionally force typed arrays to allocate outside the v8 heap. This
   // is to prevent memory pointers from being moved around that are returned by
   // Buffer::Data().