[RFC] debug_backtrace_depth(int $limit=0): int

Hi internals,

I've created a new RFC https://wiki.php.net/rfc/debug_backtrace_depth to return the depth of the current stack trace.

Inspecting the current stack trace depth is occasionally useful for

1. Manually debugging with temporary debug statements
2. Checking for potential infinite recursion or investigating reproducible reports of infinite recursion
3. Checking if code is likely to hit stack frame limits when run in environments using extensions such as Xdebug
       (https://xdebug.org/docs/all_settings#max_nesting_level , which also checks for potential infinite recursion)
       (note that Xdebug is a debugger - running php under xdebug is significantly slower than without Xdebug)

It is currently possible to compute the depth through count(debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, $limit=0)),
but this is verbose, inefficient, and harder to read compared to returning the depth directly.

Thoughts?

I plan to start voting on https://wiki.php.net/rfc/debug_backtrace_depth tomorrow.

Thanks,
Tyson

On Sat, Mar 13, 2021 at 6:30 PM tyson andre tysonandre775@hotmail.com
wrote:

Hi internals,

I've created a new RFC https://wiki.php.net/rfc/debug_backtrace_depth to
return the depth of the current stack trace.

Inspecting the current stack trace depth is occasionally useful for

1. Manually debugging with temporary debug statements
2. Checking for potential infinite recursion or investigating reproducible
   reports of infinite recursion
3. Checking if code is likely to hit stack frame limits when run in
   environments using extensions such as Xdebug
   (https://xdebug.org/docs/all_settings#max_nesting_level , which also
   checks for potential infinite recursion)
   (note that Xdebug is a debugger - running php under xdebug is
   significantly slower than without Xdebug)

It is currently possible to compute the depth through
count(debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, $limit=0)),
but this is verbose, inefficient, and harder to read compared to returning
the depth directly.

Thoughts?

Thanks,

• Tyson

There hasn't been much discussion on this one, probably because the
functionality and use cases are so specific. I'm not really convinced by
your examples.

For the purpose of printing debug logs, using an engine-provided depth is
non-ideal, because any intermediate helper functions will count towards the
depth. Tracking your own depth will result in a more meaningful/predictable
output.

For tracking down infinite recursion, isn't this what the xdebug recursion
limit is for? You'll directly get your recursive stack trace, which should
make it obvious where the infinite recursion occurs. Using
debug_backtrace_depth() for this purpose means that you actually already
need to know where you are infinitely recursing in order to place the guard.

If you want to find places where your code would hit the xdebug recursion
limit, then why not run it under xdebug and find out, rather than trying to
simulate the same behavior manually? That again requires that you actually
place relevant guards in the first place, which makes this another chicken
and egg problem.

Regards,
Nikita