Breakpoints Sometimes not resolving with Node 6.1.0

[mjbvz]

Repo

1. Install Node 6.1.0
2. Create new app.
3. Create new file (seems to repo more in larger projects and files besides the main file).
4. Set some breakpoints this new file.
5. require the file from main.
6. Try debugging.

Expected
Debugger stops at breakpoints

Actual
Breakpoints are not resolved.

Breakpoints were already less stable with Node 6.0.0, but with 6.1.0 I'm not seeing them resolved at all. Node 5.x branches work fine.

microsoft/vscode#6029

[NoelAbrahams]

Any idea when this is likely to be resolved? This issue is blocking our adoption of Node 6.1 so would appreciate a fix soon. Thanks.

[mjbvz]

I'm looking into this, but right now it is not clear what changed on the Node side of things or what the root cause of the problem is.

[mjbvz]

Quick update: The root cause seems to be a change on the node side of things, not in NTVS directly , but it is possible we were relying on bugged behavior previously. The issue is nondeterministic and more common on larger projects. I believe it also exists in Node 6.0.

I'm seeing several different behaviors:

• Sometimes everything works.
• Sometimes breakpoints are not resolved.
• Sometimes breakpoints are resolved but then cause node to emit Internal error: illegal access" when hit and we call backtrace (possibly related: Internal Error: Illegal Access  node-inspector/node-inspector#864 )

---

More specifically, here's how the flow currently works with for a new express app with the breakpoint in routes\index.js:

1. Launch node with --nolazy --debug-brk

2. Attach and request scripts from debugger.

3. We hit hit initial breakpoint on first line of main file since debug-brk is passed in.

4. Request backtrace from debugger

5. We set an initial breakpoint using the script name:

   DebuggerConnection: Request: {"command":"setbreakpoint","seq":5,"type":"request","arguments":{"line":5,"column":4,"type":"script","target":"C:\\Users\\matb.REDMOND\\Documents\\Visual Studio 2015\\Projects\\ExpressApp6\\ExpressApp6\\routes\\index.js"}}
   
   DebuggerConnection: Response: {"seq":6,"request_seq":5,"type":"response","command":"setbreakpoint","success":true,"body":{"type":"scriptName","breakpoint":2,"script_name":"C:\\Users\\matb.REDMOND\\Documents\\Visual Studio 2015\\Projects\\ExpressApp6\\ExpressApp6\\routes\\index.js","line":5,"column":4,"actual_locations":[]},"refs":[],"running":false}
   [21:50:45.6560253] AD7Engine Event: Microsoft.NodejsTools.Debugger.DebugEngine.AD7BreakpointErrorEvent (abb0ca42-f82b-4622-84e4-6903ae90f210)
   

6. This breakpoint does not resolve properly according to our logic (actual_locations is empty.) At this point, the script in question has not been fully loaded yet (We have not seen an afterCompile event emitted for it.) This happens in both 5.9 and 6.x

7. We then request continue. This resumes from the main file on line zero .

8. A bunch of afterCompile events and other stuff happens. Pretty much identical between node versions.

9. Things diverge here. On 5.9, we hit the breakpoint set in the index.js file. On 6.x, we never hit anything.

10. On 5.9, when node hits the breakpoint, we process the event. The breakpoint we set in step 5 is not understood to be fully bound by our code (even though it is fully bound in node). In ProcessBreakpointBreakAsync, we therefore destroy the existing breakpoint and recreate it based on script_id instead (176 is the id of routes/index.js):

    DebuggerConnection: Request: {"command":"setbreakpoint","seq":9,"type":"request","arguments":{"line":5,"column":4,"type":"scriptId","target":176}}
    
    DebuggerConnection: Response: {"seq":210,"request_seq":9,"type":"response","command":"setbreakpoint","success":true,"body":{"type":"scriptId","breakpoint":3,"script_id":176,"line":5,"column":4,"actual_locations":[{"line":5,"column":4,"script_id":176}]},"refs":[],"running":false}
    

---

To summarize, the core problem seems to be that the first breakpoint we set using the script name does not get picked up by Node. How our code deal with fully bound is a bit odd, and this even causes us to print an error message, but I think this is a red herring.

One other curious note: script paths are all lowercase in node 5.9 but properly cased in Node 6.0:

6.1: C:\\Users\\matb.REDMOND\\Documents\\Visual Studio 2015\\Projects\\node6debugtest\\node6debugtest\\app.js

5.9: c:\\users\\matb.redmond\\documents\\visual studio 2015\\Projects\\node6debugtest\\node6debugtest\\app.js

I'll investigate to see if this is the root cause.

[mjbvz]

Update on some of the earlier leads:

The path differences don't seem to matter. I tried using a case insensitive regex to match the file name when setting the initial breakpoint, and using a file path with no case differences except for the drive letter. These seem unrelated to the breakpoint being hit or not.

Also, I see the backtrace trigger Internal error: illegal access both when breakpoints are hit and when they are not. Setting the breakpoint inside of the express router seems to be a reliable trigger:

router.get('/', function (req, res) {
    res.render('index', { title: 'Express' }); // set breakpoint here
});

This suggests the illegal access problem is unrelated, which seems to be the conclusion of the Node-inspector thread too. It looks like there is a fix in V8 already that is getting pulled into node: nodejs/node#6928

[mousetraps]

This fix is available in v1.2 beta. Please try it out and let us know what you think! https://aka.ms/ntvslatest

[NoelAbrahams]

We've been trying out 1.2 beta with Node 6.2 and the breakpoints seem to be working so far. Thanks.