Module breakpoint 

Breakpoint stops: what a :bp marker does at runtime (§9.8).

A fault snapshot is taken while the stack is unwinding and is read after every language frame has gone (see crate::crash_snapshot). A breakpoint is the other case: the frames are still claimed, the program is still in the middle of them, and the whole point is to go back afterwards. So this module is deliberately not a second fault path — it is a call out to the host and a return.

The handler is given a snapshot and nothing else, and that is the design

BreakpointHandler takes a &BreakpointStop and no *mut RuntimeContext. It has no heap pointer, no allocator, no way to run generated code — so it cannot trigger a collection, and that is a structural fact rather than a rule a host has to remember.

That matters because of what the stop hands over. BreakpointStop::frames is a deep copy of the live debug chain, and its GcRefs are only as valid as the objects they name. Values below the debug stack’s top are ADR-106’s weak arm — every collection clears the slots whose objects it reclaimed — so at the instant the copy is taken every reference in it is live. Keeping it that way for the duration of the stop needs one thing: that no collection happens while the host is looking. Withholding the context is how that is guaranteed, and it is why the snapshot does not need to be registered as a root set the way a fault snapshot does (which the host holds across restart, p EXPR and everything else that allocates).

Detaching, and why there is no kill

Resume has two arms. Continue returns to the program. Detach returns to the program and disarms every later stop, which is what “quit the debugger” means from inside a live run.

There is no third arm that ends the program, because there is nothing sound to do with the frames: §9.2 forbids unwinding Rust through JIT frames, and the fault epilogue that can unwind them is reached by raising a fault — which would report the program as having failed when it did not. A host that wants the run over can exit the process from its handler; the language will not pretend a stop is a fault.

Structs

BreakpointStop

One :bp stop, as the host sees it.

Enums

Resume

What the host wants done after a stop.

Functions

breakpoints_detached

Whether a stop has detached (a Resume::Detach answer). The host’s way to tell a run the user walked away from apart from one that simply had no markers left.

clear_breakpoint_handler

Forget any installed handler, so every later :bp is a no-op.

install_breakpoint_handler

Install the host’s breakpoint handler, armed and with a fresh hit count.

Type Aliases

BreakpointHandler

A host’s breakpoint handler: given a stop, answers what to do next.