Fix build with Python 3.4 (PR python/16784)

From: Simon Marchi <simon.marchi@ericsson.com>

  On 2014-12-04 01:14 PM, Pedro Alves wrote:
> On 11/26/2014 01:47 PM, Simon Marchi wrote:
>> The type of the function pointer PyOS_ReadlineFunctionPointer (part of the
>> Python C API), which we use, slightly changed starting with Python 3.4. The
>> signature when from
> 
> "went from"
> 
>> I changed the signature of deprecated_readline_hook. I would've changed any
>> user of it, but it seems like nothing is using it,
> 
> You'd probably find it in the insight/gdbtk code.
> 
>> --- a/gdb/python/py-gdb-readline.c
>> +++ b/gdb/python/py-gdb-readline.c
>> @@ -26,10 +26,13 @@
>>     cases, sys_stdin and sys_stdout are always stdin and stdout
>>     respectively, as far as I can tell; they are ignored and
>>     command_line_input is used instead.  */
>> -
>>  static char *
> 
> Don't lose the empty line.
> 
>>  gdbpy_readline_wrapper (FILE *sys_stdin, FILE *sys_stdout,
>> +#if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION >= 4
>> +			const char *prompt)
>> +#else
>>  			char *prompt)
>> +#endif
>>
> 
>> @@ -938,6 +938,8 @@ command_line_input (char *prompt_arg, int repeat, char *annotation_suffix)
>>        strcat (local_prompt, "\n\032\032");
>>        strcat (local_prompt, annotation_suffix);
>>        strcat (local_prompt, "\n");
>> +
>> +      prompt_arg = local_prompt;
> 
> I think it'd be even clearer if we avoided changing
> the variable that is called "arg".  How about we add:
> 
>    const char *prompt = prompt_arg;
> 
> at the top, and then use "prompt" throughout, where
> you're using "prompt_arg"?
> 
> The 'local_prompt' variable could move to the "annotation_level > 1"
> block too, for clarity.
> 
> Thanks,
> Pedro Alves

Hi Pedro,

Here is the v2, with changes according to your comments.

From 8ccae8f39992e7515711d6fc193f1d68cb47eaf8 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@ericsson.com>
Date: Tue, 25 Nov 2014 21:02:15 -0500
Subject: [PATCH v2] Fix build with Python 3.4 (PR python/16784)

The type of the function pointer PyOS_ReadlineFunctionPointer (part of the
Python C API), which we use, slightly changed starting with Python 3.4. The
signature went from

PyAPI_DATA(char) *(*PyOS_ReadlineFunctionPointer)(FILE *, FILE *, char *);

to

PyAPI_DATA(char) *(*PyOS_ReadlineFunctionPointer)(FILE *, FILE *, const char *);

The parameter that changed is the prompt text.

This commits adjust gdb accordingly by making the prompt_arg parameter
const, as well as the fallouts of that. I needed to rework how
annotations are added to the prompt, since the it is now const. If
annotations are enabled, it will make a copy of the prompt overwrite the
prompt variable that is used throughout the function. Otherwise, no copy
is done and the original prompt_arg value is passed.

I changed the signature of deprecated_readline_hook. I would've changed any
user of it, but it seems like nothing is using it,

Built-tested with python 2.7.x, 3.3.y and 3.4.z.

New in v2:
* Formatting.
* Don't change the prompt_arg argument, use a local variable instead.
* Move local_prompt in a narrower scope.

Signed-off-by: Simon Marchi <simon.marchi@ericsson.com>
---
 gdb/defs.h                   |  8 ++++----
 gdb/event-top.c              |  2 +-
 gdb/event-top.h              |  2 +-
 gdb/python/py-gdb-readline.c |  4 ++++
 gdb/top.c                    | 30 +++++++++++++++++-------------
 5 files changed, 27 insertions(+), 19 deletions(-)

Fix build with Python 3.4 (PR python/16784)

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