[PATCH] gdb: improve command completion for 'print', 'x', and 'display'

[Simon Marchi]

On 2020-11-16 10:42 a.m., Andrew Burgess wrote:
> The /FMT specification on the print command currently breaks command
> completion, so:
> 
>   (gdb) p var.<TAB><TAB>
>   .... list of fields in var .....
> 
> But,
> 
>   (gdb) p/d var.<TAB><TAB>
>   ..... list of all symbols .....
> 
> After this commit this issue is now resolved.
> 
> There are some other details around tab-completion and /FMT which
> hopefully this commit improves.  So, before:
> 
>   (gdb) p/<TAB><TAB>
>   .... lists all symbols .....
> 
> After:
> 
>   (gdb) p/<TAB><TAB>		# Nothing changes...
> 
> The thinking here is that after a / the user must type a FMT, but we
> don't offer tab completion on FMT characters.  Placing a symbol
> directly after a / will not do what the user expects, so offering that
> seems wrong.
> 
> Similarly, before we had:
> 
>   (gdb) p/d<TAB><TAB>
>   ... lists all symbols starting with 'd' ....
> 
> But afterwards:
> 
>   (gdb) p/d<TAB><TAB>		# Adds a single space, so we get:
>   (gdb) p/d <CURSOR>
> 
> As before, typing a symbol where FMT is expected will not do what the
> user expects.  If the user has added a FMT string then upon tab
> completion GDB assumes the FMT string is complete and prepares the
> user to type an expression.
> 
> In this commit I have also added completion functions for the 'x' and
> 'display' commands.  These commands also support /FMT specifiers and
> so share some code with 'print'.
> 
> gdb/ChangeLog:
> 
> 	* printcmd.c: Include 'safe-ctype.c'.
> 	(skip_over_slash_fmt): New function.
> 	(print_command_completer): Call skip_over_slash_fmt.
> 	(display_and_x_command_completer): New function.
> 	(_initialize_printcmd): Add command completion for 'x' and
> 	'display'.
> 
> gdb/testsuite/ChangeLog:
> 
> 	* gdb.base/completion.exp: Add new tests.
> ---
>  gdb/ChangeLog                         |  9 +++
>  gdb/printcmd.c                        | 81 ++++++++++++++++++++++++++-
>  gdb/testsuite/ChangeLog               |  4 ++
>  gdb/testsuite/gdb.base/completion.exp | 26 +++++++++
>  4 files changed, 118 insertions(+), 2 deletions(-)

I noticed this warning in the code added by this patch, I think it's not a false positive:

/home/simark/src/binutils-gdb/gdb/printcmd.c: In function ‘bool skip_over_slash_fmt(completion_tracker&, const char**)’:
/home/simark/src/binutils-gdb/gdb/printcmd.c:1285:14: warning: ‘in_fmt’ may be used uninitialized in this function [-Wmaybe-uninitialized]
 1285 |       return in_fmt;
      |              ^~~~~~


Simon