Heads-up: `Debugger#restartFrame` now working again

We recently re-implemented the Debugger#restartFrame CDP method that allows restarting of functions while paused (CL).

This is just a heads-up in case folks are interested in bringing this feature also to JS debugging in VS Code.

The new semantics are a bit different though, in that V8 won’t always allow functions to be restarted. We communicate this info in the Debugger.paused event where each call frame now has a canBeRestarted flag. This info is accurate as long as the user doesn’t mess with stack between pausing and requesting a frame restart. Calling the restartFrame CDP method also continues execution immediately, but will pause automatically at the beginning of the restarted function.

[szuend]

Let’s say you have a function foo and a function myCallback in your script and foo calls some Web/Node API:

function foo() {
  //...
  someNodeAPI(function myCallback() {
    debugger;
  });

When stopped in myCallback you won’t be able to restart foo (assuming its still on the stack).

As a side note, this is different to e.g. async/generator functions, which can’t be restarted for other reasons.

[szuend]

It’s a bit technical: Essentially we can’t restart across C++ frames (because destructors need to run when dropping C++ frames), which means restarting across Web APIs or Node APIs is now prohibited.