v8_inspector: Support the V8 debugger from within VM contexts

[ide]

This is a feature request to support Node 6.3.0's V8 inspector capability (node --inspect) from within the vm module's contexts. For example:

vm.runInNewContext(code, sandbox, {
  inspect: 9999, // same as --inspect=9999
});

If it's not possible to make individual contexts inspectable, it'd also meet our needs to make other contexts inspectable if the parent Node process is running with --inspect. Currently code that runs in other contexts isn't debuggable (ex: debugger statements are ignored).

[cpojer]

node --inspect also doesn't stop for debugger; statements.

Repro:

var vm = require('vm');
new vm.Script('debugger;').runInContext(vm.createContext());
debugger;

[ide]

@cpojer are you running Node with the --debug-brk option? You need that so that Node waits for you to connect the Blink Inspector since debugger statements are no-ops unless there is a debugger actively attached.

[cpojer]

@ide yes, please see jestjs/jest#1652 for more details.

[jkrems]

Quoting @bmeck (https://twitter.com/bradleymeck/status/790571493579116546):

basically you need to setup

node/deps/v8_inspector/third_party/v8_inspector/platform/v8_inspector/V8InspectorImpl.cpp

Line 199 in db1087c

void V8InspectorImpl::contextCreated(const V8ContextInfo& info)

properly to work w/ vm module

[bmeck]

can be based upon https://github.com/bmeck/node/tree/inspect-contexts , don't really have time to figure out segfaults currently but would need tests for sure to ensure GC properly works on this.

[ofrobots]

The branch from @bmeck looks like a good starting point. This would be a really neat contribution.

/cc @nodejs/v8-inspector.

[bmeck]

i'll take this over, it seems like there is also a bug with the inspector not being synced the contexts on connect which makes this less trivial since we need to rejig the handshaking.