interesting, i guess we just send it anyways

    # A boolean flag which tells if the kernel supports debugging in the notebook.
    # Default is False.
    # Deprecated as replaced by 'supported_features'=['debugger'] (see below).
    'debugger': bool,

yep we're sending both

is the explicit drop() meaningful?

It seems like good practice

Since all of these are only used for notebooks, I was kind of confused that they are here at all for console mode.

It might be nice to wrap these up in an optional struct, like

struct JupyterDap {
    dap: Arc<Mutex<Dap>>,
    dap_handler: DapJupyterHandler,
}

which is then Option<JupyterDap> on Control

and then you can use the precence of that field rather than matches!(self.session_mode, SessionMode::Notebook) to make decisions in other parts of the codebase

I'm intending to get breakpoint sync via the jupyter handler even in Console mode.

For now I made the handler optional, but in the future we'll have a specialised handler for consoles too.

Wouldn't it be cleaner to just wrap DapBackendEvent::BreakpointState { in self.send_backend_event()?

You avoid the events vec alltogether, I think

I've added a comment explaining why it's structured this way:

        // Collect events first: `bp_list` borrows from `self.breakpoints`,
        // which prevents calling `&mut self` methods like `send_backend_event()`.

I'm getting that feeling that iopub_seq should be wrapped in a Cell or something like that so it can be interiorly mutable allowing send_backend_event() to just be &self, because it really doesn't feel like you should need &mut self to do a send_backend_event(), and the counter feels like an internal detail

This seems like a very unnecessary extra { scope?

borrow-checker

nope

    pub fn verify_breakpoint(&mut self, uri: &UrlId, id: &str) {
        let Some((_, bp_list)) = self.breakpoints.get_mut(uri) else {
            return;
        };
        let Some(bp) = bp_list.iter_mut().find(|bp| bp.id.to_string() == id) else {
            return;
        };

        if !matches!(bp.state, BreakpointState::Unverified) {
            return;
        }

        bp.state = BreakpointState::Verified;

        let event = DapBackendEvent::BreakpointState {
            id: bp.id,
            line: bp.line,
            verified: true,
            message: None,
        };

        self.send_backend_event(event);
    }

could probably avoid the collect() and just do .into_iter() on the filter_map result and loop over that?

borrow-checker

we could also just use someone else's?

We also implement it on the frontend side. We could use the murmur2 crate, or just keep this one. I'm going with the latter since it's tested already.

I also like the tempdir crate for this kind of thing?

Here we're creating a directory with a very specific pattern that remains valid for the whole session.

I think you can do all that with the tempfile crate (not tempdir, sorry)

But regardless, it looks like its default is to just use std::env::temp_dir as the starting location to put the tempdir in, so I don't think it really matters

But based on your comments im now interested in the timing - do we need to trigger this lazylock before we start R up?