[PING][PATCH][gdb] Make execute_command_to_string return string on throw

[Tom de Vries via Gdb-patches <gdb-patches@sourceware.org>]

On 9/11/21 2:02 PM, Tom de Vries wrote:
> Hi,
> 
> The pattern for using execute_command_to_string is:
> ...
>   std::string output;
>   output = execute_fn_to_string (fn, term_out);
> ...
> 
> This results in a problem when using it in a try/catch:
> ...
>   try
>     {
>       output = execute_fn_to_string (fn, term_out)
>     }
>   catch (const gdb_exception &e)
>     {
>       /* Use output.  */
>     }
> ...
> 
> If an expection was thrown during execute_fn_to_string, then the output
> remains unassigned, while it could be worthwhile to known what output was
> generated by gdb before the expection was thrown.
> 
> Fix this by returning the string using a parameter instead:
> ...
>   execute_fn_to_string (output, fn, term_out)
> ...
> 
> Also add a variant without string parameter, to support places where the
> function is used while ignoring the result:
> ...
>   execute_fn_to_string (fn, term_out)
> ...
> 
> Tested on x86_64-linux.
> 
> Any comments?
> 

Ping.

Thanks,
- Tom

> [gdb] Make execute_command_to_string return string on throw
> 
> ---
>  gdb/complaints.c    |  4 ++--
>  gdb/gdbcmd.h        | 12 +++++++++---
>  gdb/guile/guile.c   |  2 +-
>  gdb/python/python.c |  6 +++---
>  gdb/stack.c         |  4 ++--
>  gdb/thread.c        |  5 +++--
>  gdb/top.c           | 34 +++++++++++++++++++++++++++-------
>  7 files changed, 47 insertions(+), 20 deletions(-)
> 
> diff --git a/gdb/complaints.c b/gdb/complaints.c
> index 525a3a7eacf..a823fcb0020 100644
> --- a/gdb/complaints.c
> +++ b/gdb/complaints.c
> @@ -91,7 +91,7 @@ test_complaints ()
>    do									\
>      {									\
>        std::string output;						\
> -      output = execute_fn_to_string ([]() { complaint (STR); }, false);	\
> +      execute_fn_to_string (output, []() { complaint (STR); }, false);	\
>        std::string expected						\
>  	= _("During symbol reading: ") + std::string (STR "\n");	\
>        SELF_CHECK (output == expected);					\
> @@ -102,7 +102,7 @@ test_complaints ()
>    do									\
>      {									\
>        std::string output;						\
> -      output = execute_fn_to_string ([]() { complaint (STR); }, false);	\
> +      execute_fn_to_string (output, []() { complaint (STR); }, false);	\
>        SELF_CHECK (output.empty ());					\
>        SELF_CHECK (counters[STR] == CNT);				\
>      } while (0)
> diff --git a/gdb/gdbcmd.h b/gdb/gdbcmd.h
> index 27550c1faee..05ffd7fd0ee 100644
> --- a/gdb/gdbcmd.h
> +++ b/gdb/gdbcmd.h
> @@ -145,7 +145,8 @@ extern void execute_fn_to_ui_file (struct ui_file *file, std::function<void(void
>     (e.g. with styling).  When TERM_OUT is false raw output will be collected
>     (e.g. no styling).  */
>  
> -extern std::string execute_fn_to_string (std::function<void(void)> fn, bool term_out);
> +extern void execute_fn_to_string (std::string &res,
> +				  std::function<void(void)> fn, bool term_out);
>  
>  /* As execute_fn_to_ui_file, but run execute_command for P and FROM_TTY.  */
>  
> @@ -154,8 +155,13 @@ extern void execute_command_to_ui_file (struct ui_file *file,
>  
>  /* As execute_fn_to_string, but run execute_command for P and FROM_TTY.  */
>  
> -extern std::string execute_command_to_string (const char *p, int from_tty,
> -					      bool term_out);
> +extern void execute_command_to_string (std::string &res, const char *p,
> +				       int from_tty, bool term_out);
> +
> +/* As execute_command_to_string, but ignore resulting string.  */
> +
> +extern void execute_command_to_string (const char *p,
> +				       int from_tty, bool term_out);
>  
>  extern void print_command_line (struct command_line *, unsigned int,
>  				struct ui_file *);
> diff --git a/gdb/guile/guile.c b/gdb/guile/guile.c
> index a28dee37ed8..8ba840cba6a 100644
> --- a/gdb/guile/guile.c
> +++ b/gdb/guile/guile.c
> @@ -302,7 +302,7 @@ gdbscm_execute_gdb_command (SCM command_scm, SCM rest)
>  
>        scoped_restore preventer = prevent_dont_repeat ();
>        if (to_string)
> -	to_string_res = execute_command_to_string (command, from_tty, false);
> +	execute_command_to_string (to_string_res, command, from_tty, false);
>        else
>  	execute_command (command, from_tty);
>  
> diff --git a/gdb/python/python.c b/gdb/python/python.c
> index 5918bb414a3..34c1be76a16 100644
> --- a/gdb/python/python.c
> +++ b/gdb/python/python.c
> @@ -1888,11 +1888,11 @@ namespace selftests {
>  static void
>  test_python ()
>  {
> -#define CMD execute_command_to_string ("python print(5)", 0, true);
> +#define CMD(S) execute_command_to_string (S, "python print(5)", 0, true)
>  
>    std::string output;
>  
> -  output = CMD;
> +  CMD (output);
>    SELF_CHECK (output == "5\n");
>    output.clear ();
>  
> @@ -1901,7 +1901,7 @@ test_python ()
>      = make_scoped_restore (&gdb_python_initialized, 0);
>    try
>      {
> -      output = CMD;
> +      CMD (output);
>      }
>    catch (const gdb_exception &e)
>      {
> diff --git a/gdb/stack.c b/gdb/stack.c
> index 516e4d45696..edfda3a4e55 100644
> --- a/gdb/stack.c
> +++ b/gdb/stack.c
> @@ -3026,8 +3026,8 @@ frame_apply_command_count (const char *which_command,
>  	       set to the selected frame.  */
>  	    scoped_restore_current_thread restore_fi_current_frame;
>  
> -	    cmd_result = execute_command_to_string
> -	      (cmd, from_tty, gdb_stdout->term_out ());
> +	    execute_command_to_string
> +	      (cmd_result, cmd, from_tty, gdb_stdout->term_out ());
>  	  }
>  	  fi = get_selected_frame (_("frame apply "
>  				     "unable to get selected frame."));
> diff --git a/gdb/thread.c b/gdb/thread.c
> index 10c3dcd6991..019c658bc47 100644
> --- a/gdb/thread.c
> +++ b/gdb/thread.c
> @@ -1457,8 +1457,9 @@ thr_try_catch_cmd (thread_info *thr, const char *cmd, int from_tty,
>  
>    try
>      {
> -      std::string cmd_result = execute_command_to_string
> -	(cmd, from_tty, gdb_stdout->term_out ());
> +      std::string cmd_result;
> +      execute_command_to_string
> +	(cmd_result, cmd, from_tty, gdb_stdout->term_out ());
>        if (!flags.silent || cmd_result.length () > 0)
>  	{
>  	  if (!flags.quiet)
> diff --git a/gdb/top.c b/gdb/top.c
> index 7e95ed3969c..ff240eed657 100644
> --- a/gdb/top.c
> +++ b/gdb/top.c
> @@ -728,13 +728,22 @@ execute_fn_to_ui_file (struct ui_file *file, std::function<void(void)> fn)
>  
>  /* See gdbcmd.h.  */
>  
> -std::string
> -execute_fn_to_string (std::function<void(void)> fn, bool term_out)
> +void
> +execute_fn_to_string (std::string &res, std::function<void(void)> fn,
> +		      bool term_out)
>  {
>    string_file str_file (term_out);
>  
> -  execute_fn_to_ui_file (&str_file, fn);
> -  return std::move (str_file.string ());
> +  try {
> +    execute_fn_to_ui_file (&str_file, fn);
> +  } catch (...) {
> +    /* Finally.  */
> +    res = std::move (str_file.string ());
> +    throw;
> +  }
> +
> +  /* And finally.  */
> +  res = std::move (str_file.string ());
>  }
>  
>  /* See gdbcmd.h.  */
> @@ -748,12 +757,23 @@ execute_command_to_ui_file (struct ui_file *file,
>  
>  /* See gdbcmd.h.  */
>  
> -std::string
> +void
> +execute_command_to_string (std::string &res, const char *p, int from_tty,
> +			   bool term_out)
> +{
> +  execute_fn_to_string (res, [=]() { execute_command (p, from_tty); },
> +			term_out);
> +}
> +
> +/* See gdbcmd.h.  */
> +
> +void
>  execute_command_to_string (const char *p, int from_tty,
>  			   bool term_out)
>  {
> -  return
> -    execute_fn_to_string ([=]() { execute_command (p, from_tty); }, term_out);
> +  std::string dummy;
> +  execute_fn_to_string (dummy, [=]() { execute_command (p, from_tty); },
> +			term_out);
>  }
>  \f
>  /* When nonzero, cause dont_repeat to do nothing.  This should only be
>