Special case array length reporting

Matt Loring · Matt Loring · commit fedd5f4ec9b8 · 2016-06-08T14:19:23.000-07:00
diff --git a/lib/state.js b/lib/state.js
@@ -460,7 +460,10 @@ StateResolver.prototype.getMirrorProperties_ = function(mirror) {
 
 StateResolver.prototype.resolveMirrorProperty_ = function(property) {
   var name = String(property.name());
-  if (property.isNative()) {
+  // Array length must be special cased as it is a native property that
+  // we know to be safe to evaluate which is not generally true.
+  var isArrayLen = property.mirror_.isArray() && name === 'length';
+  if (property.isNative() && !isArrayLen) {
     return {
       name: name,
       varTableIndex: NATIVE_PROPERTY_MESSAGE_INDEX
diff --git a/test/test-v8debugapi.js b/test/test-v8debugapi.js
@@ -38,6 +38,7 @@ var config = require('../config.js').debug;
 var StatusMessage = require('../lib/apiclasses.js').StatusMessage;
 var scanner = require('../lib/scanner.js');
 var path = require('path');
+var semver = require('semver');
 
 function stateIsClean(api) {
   assert.equal(api.numBreakpoints_(), 0,
@@ -543,6 +544,40 @@ describe('v8debugapi', function() {
       });
     });
 
+    it('should work with array length despite being native', function(done) {
+      if (semver.satisfies(process.version, '<1.0')) {
+        return done();
+      }
+      var bp  = {
+        id: breakpointInFoo.id,
+        location:  { path: 'test-v8debugapi.js', line: 5 },
+        expressions: ['A']
+      };
+      api.set(bp, function(err) {
+        assert.ifError(err);
+        api.wait(bp, function(err) {
+          assert.ifError(err);
+
+          var arrEnv = bp.evaluatedExpressions[0];
+          assert.equal(arrEnv.name, 'A');
+          var envVal = bp.variableTable[arrEnv.varTableIndex];
+          var found = false;
+          envVal.members.forEach(function(member) {
+            if (member.name === 'length') {
+              assert(!member.varTableIndex);
+              assert.equal(member.value, 3);
+              found = true;
+            }
+          });
+          assert(found);
+
+          api.clear(bp);
+          done();
+        });
+        process.nextTick(function() {foo();});
+      });
+    });
+
     it('should limit string length', function(done) {
       var bp = {
         id: 'fake-id-124',
