Re: patch for #14363

[Phil Muldoon <pmuldoon@redhat.com>]

On 08/02/2012 05:21 PM, Oliver Buchtala wrote:
> From 05a921d423793db93dfead59c9fe12d342f55d75 Mon Sep 17 00:00:00 2001
> From: Oliver Buchtala <oliver.buchtala@googlemail.com>
> Date: Wed, 1 Aug 2012 21:59:43 +0200
> Subject: [PATCH] Adapt py-prettyprint to inform pretty-printer about current
>  recursion level.
> 
> ---
>  gdb/python/py-prettyprint.c  |    3 +++
>  gdb/python/python-internal.h |    1 +
>  gdb/python/python.c          |    2 ++
>  3 files changed, 6 insertions(+)

Thanks.

Needs a GNU style ChangeLog, testcase and documentation
additions.

I am having trouble understanding what you are doing with "recurse"
attribute.  From valprint.c, in the GDB sources (which calls
apply_val_pretty_printer, among others):

   "RECURSE indicates the amount of indentation to supply before
   continuation lines; this amount is roughly twice the value of
   RECURSE."

So I am not sure that this is the value you want?  Anyway, I think you
want the number of recursions for that printer, not the recurse value
being supplied to apply_val_pretty_printer.  A testcase would help
here to understand your intention.

> diff --git a/gdb/python/py-prettyprint.c b/gdb/python/py-prettyprint.c
> index 86d4f2c..d5c6b66 100644
> --- a/gdb/python/py-prettyprint.c
> +++ b/gdb/python/py-prettyprint.c
> @@ -476,6 +476,9 @@ print_children (PyObject *printer, const char *hint,
>    if (! PyObject_HasAttr (printer, gdbpy_children_cst))
>      return;
>  
> +  if ( PyObject_HasAttr (printer, gdbpy_level_cst))
> +    PyObject_SetAttr(printer, gdbpy_level_cst, PyInt_FromLong((long) recurse));
> +

There are a few issues with this patch hunk:

* It is not clear in the documentation, but PyInt_FromLong can raise a
  PyErr_NoMemory exception, so you need to NULL check the return and
  dispatch the exception appropriately.

* This leaks a reference from PyInt_FromLong.  PyObject_SetAttr
  increments the reference count of the right side of "=" Python
  equivalent (IE foo.bar = baz), which in this case is the integer. So
  the transient reference from PyInt_FromLong will last forever.  You
  you need to assign the results of PyInt_FromLong to a variable and
  call Py_DECREF on it after the "PyObject_SetAttr" call.

* PyObject_SetAttr can fail, so the code needs to deal with this
  contingency.

* Why PyInt_FromLong over PyLong_FromLong?

Beyond the patch fixes, is it not possible to count the recursion
level by some internal bookkeeping in the printer?  I have no problem
with including the attribute if it is helpful, or clearer to solve the
problem, but I am curious if you have tried the alternative, if
possible?

Cheers,

Phil