[slime-devel] [PATCH] hiding swank frames from debugger backtrace on Allegro

[Stas Boukarev]

Luís Oliveira <luismbo at gmail.com> writes:

> Hello,
>
> As you well know, SLIME's debugger, when invoked, will inevitably add
> some frames to the current stack, which SWANK attempts to hide. On
> Allegro, when signalling an error from the REPL, those extra frames look
> something like this:
>
>   0: ((FLET (:TOP-LEVEL-FORM "swank-allegro.lisp" 4123) SWANK-
>        BACKEND:CALL-WITH-DEBUGGING-ENVIRONMENT) #<Function (:INTERNAL
>        SWANK::DEBUG-IN-EMACS 0)>)
>   1: (SWANK-BACKEND:CALL-WITH-DEBUGGING-ENVIRONMENT #<Function
>        (:INTERNAL SWANK::DEBUG-IN-EMACS 0)>)
>   2: (SWANK::DEBUG-IN-EMACS #<SIMPLE-ERROR @ #x218114d2>)
>   3: (SWANK:INVOKE-SLIME-DEBUGGER #<SIMPLE-ERROR @ #x218114d2>)
>   4: ((:INTERNAL SWANK:SWANK-DEBUGGER-HOOK 1))
>   5: ((:INTERNAL (:TOP-LEVEL-FORM "swank-backend.lisp" 32198) 0)
>        #<Function SWANK-DEBUGGER-HOOK> #<Closure (:INTERNAL SWANK:SWANK-
>        DEBUGGER-HOOK 1) @ #x218115f2>)
>   6: (SWANK-BACKEND:CALL-WITH-DEBUGGER-HOOK #<Function SWANK-
>        DEBUGGER-HOOK> #<Closure (:INTERNAL SWANK:SWANK-DEBUGGER-HOOK 1)
>        @ #x218115f2>)
>   7: (SWANK:SWANK-DEBUGGER-HOOK #<SIMPLE-ERROR @ #x218114d2> #<Function
>        SWANK-DEBUGGER-HOOK>)
>   8: (ERROR "foo")
>
>
> In this case, FIND-TOPLEVEL in swank-allegro.lisp successfully figures
> out that the first 8 frames are to be hidden.
>
> However, if the error comes from some other thread -- this can be
> reproduced via (mp:process-run-function nil (lambda () (error "foo")))
> for example -- there will a couple of extra frames:
>
>   0: ((FLET (:TOP-LEVEL-FORM "swank-allegro.lisp" 4123) SWANK-
>        BACKEND:CALL-WITH-DEBUGGING-ENVIRONMENT) #<Function (:INTERNAL
>        SWANK::DEBUG-IN-EMACS 0)>)
>   1: (SWANK-BACKEND:CALL-WITH-DEBUGGING-ENVIRONMENT #<Function
>        (:INTERNAL SWANK::DEBUG-IN-EMACS 0)>)
>   2: (SWANK::DEBUG-IN-EMACS #<SIMPLE-ERROR @ #x21552f92>)
>   3: ((:INTERNAL SWANK:INVOKE-SLIME-DEBUGGER 0))
>   4: ((:INTERNAL (:TOP-LEVEL-FORM "swank-backend.lisp" 32198) 0)
>        #<Function SWANK-DEBUGGER-HOOK> #<Closure (:INTERNAL
>        SWANK:INVOKE-SLIME-DEBUGGER 0) @ #x215530e2>)
>   5: (SWANK-BACKEND:CALL-WITH-DEBUGGER-HOOK #<Function SWANK-
>        DEBUGGER-HOOK> #<Closure (:INTERNAL SWANK:INVOKE-SLIME-DEBUGGER
>        0) @ #x215530e2>)
>   6: ((:INTERNAL SWANK:INVOKE-SLIME-DEBUGGER 3))
>   7: (SWANK::CALL-WITH-BINDINGS ..)
>   8: (SWANK:INVOKE-SLIME-DEBUGGER #<SIMPLE-ERROR @ #x21552f92>)
>   9: ((:INTERNAL SWANK:SWANK-DEBUGGER-HOOK 1))
>  10: ((:INTERNAL (:TOP-LEVEL-FORM "swank-backend.lisp" 32198) 0)
>        #<Function SWANK-DEBUGGER-HOOK> #<Closure (:INTERNAL SWANK:SWANK-
>        DEBUGGER-HOOK 1) @ #x2155309a>)
>  11: (SWANK-BACKEND:CALL-WITH-DEBUGGER-HOOK #<Function SWANK-
>        DEBUGGER-HOOK> #<Closure (:INTERNAL SWANK:SWANK-DEBUGGER-HOOK 1)
>        @ #x2155309a>)
>  12: (SWANK:SWANK-DEBUGGER-HOOK #<SIMPLE-ERROR @ #x21552f92> #<Function
>        SWANK-DEBUGGER-HOOK>)
>  13: (ERROR "foo")
>
>
> Because FIND-TOPLEVEL currently only looks at the first eleven frames,
> it will fail to find frame #12 in the stacktrace above. Consequently,
> the extra debugger frames won't be hidden.
>
> The attached patch fixes this by looking a bit further (30 frames)
> taking care not to fail on small stacks.
>
> I considered the idea of not hard-coding an arbitrary limit, but in the
> end went with the more conservative fix since walking through a very
> large stack takes a while. (However, it seems unlikely that
> FIND-TOPFRAME would ever be called in a context where
> SWANK-DEBUGGER-HOOK is not on the stack, modulo protocol changes that
> would break the whole scheme anyway.)
Applied, thanks.

-- 
With best regards, Stas.