Re: [PATCH 09/16] gdb/python: change escaping rules when setting arguments

[Eli Zaretskii <eliz@gnu.org>]

> From: Andrew Burgess <aburgess@redhat.com>
> Cc: Andrew Burgess <aburgess@redhat.com>, Michael Weghorn <m.weghorn@posteo.de>
> Date: Tue,  9 Jan 2024 14:26:32 +0000
> 
> It is possible to set an inferior's arguments through the Python API
> by assigning to the gdb.Inferior.arguments attribute.
> 
> This attribute can be assigned a string, in which case the string is
> taken verbatim as the inferior's argument string.  Or this attribute
> can be assigned a sequence, in which case the members of the sequence
> are combined (with some escaping applied) to create the inferior's
> argument string.
> 
> Currently, the when the arguments from a Python list are escaped, we
> use escape_shell_characters.  I suspect the reasons for this are
> mostly accidental.
> 
> When the gdb.Inferior.arguments attribute was introduced in commit:
> 
>   commit 3153113252f3b949a159439a17e88af8ff0dce30
>   Date:   Mon May 1 13:53:59 2023 -0600
> 
>       Add attributes and methods to gdb.Inferior
> 
> GDB's inferior::set_args method called construct_inferior_arguments,
> and construct_inferior_arguments didn't take an escaping function as a
> parameter, the only option was escape_shell_characters as that was the
> escaping hard-coded into construct_inferior_arguments.  The commit
> message makes no comments for or against escaping of special shell
> characters, and no tests were added that checked this behaviour.  All
> of this leads me to think that the handling of special shell
> characters wasn't really considered (an understandable oversight).
> 
> But I'd like to consider it, and I think the current behaviour is not
> ideal.
> 
> Consider this case:
> 
>   (gdb) python gdb.selected_inferior().arguments = ['$VAR']
>   (gdb) show args
>   Argument list to give program being debugged when it is started is "\$VAR".
> 
> This means that when the inferior is run it will see literal '$VAR' as
> its argument.  If instead, the user wants to pass the shell expanded
> value of $VAR to the inferior, there's no way to achieve this result
> using the list assignment method.
> 
> In this commit I propose that we change this behaviour so that we
> instead see this:
> 
>   (gdb) python gdb.selected_inferior().arguments = ['$VAR']
>   (gdb) show args
>   Argument list to give program being debugged when it is started is "$VAR".
> 
> Now the '$' character is not escaped.  If the inferior is started
> under a shell then the user will see the shell expanded value of
> '$VAR'.
> 
> Of course, if the user wants to pass a literal '$VAR' (with no
> expansion) then they can do:
> 
>   (gdb) python gdb.selected_inferior().arguments = ['\$VAR']
> 
> This actually feels more natural to me, the user writes the argument
> as they would present it to a shell.
> 
> So, after this commit, GDB only escapes quote characters and white
> space characters.  This keeps some level of backward compatibility
> with the existing behaviour (for things other than shell special
> characters), but also seems natural, from the user's point of view,
> the arguments they are providing are already quoted (by Python's
> string quotes) so there's no need to quote white space.  It's only
> when GDB converts the Python sequence into a single string that the
> white space actually needs quoting.
> 
> There are tests for the updated functionality, and I've updated the
> docs and added a NEWS entry.
> ---
>  gdb/NEWS                                 |  4 +++
>  gdb/doc/python.texi                      |  7 +++--
>  gdb/python/py-inferior.c                 |  2 +-
>  gdb/testsuite/gdb.python/py-inferior.exp | 36 ++++++++++++++++++++----
>  gdbsupport/common-inferior.cc            | 14 +++++++++
>  gdbsupport/common-inferior.h             |  5 ++++
>  6 files changed, 60 insertions(+), 8 deletions(-)

The documentation parts are okay, thanks.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>