[PATCH v2 1/4] Cygwin: console: Add workaround for broken IL/DL in xterm mode.

[Jon Turney]

On 26/02/2020 15:32, Takashi Yano wrote:
> - Cygwin console with xterm compatible mode causes problem reported
>    in https://www.cygwin.com/ml/cygwin-patches/2020-q1/msg00212.html
>    if background/foreground colors are set to gray/black respectively
>    in Win10 1903/1909. This is caused by "CSI Ps L" (IL), "CSI Ps M"
>    (DL) and "ESC M" (RI) control sequences which are broken. This
>    patch adds a workaround for the issue.
> ---
>   winsup/cygwin/fhandler_console.cc | 156 +++++++++++++++++++++++++++++-
>   winsup/cygwin/wincap.cc           |  10 ++
>   winsup/cygwin/wincap.h            |   2 +
>   3 files changed, 166 insertions(+), 2 deletions(-)
> 
> diff --git a/winsup/cygwin/fhandler_console.cc b/winsup/cygwin/fhandler_console.cc
> index 328424a7d..c2198ea1e 100644
> --- a/winsup/cygwin/fhandler_console.cc
> +++ b/winsup/cygwin/fhandler_console.cc
> @@ -57,6 +57,16 @@ bool NO_COPY fhandler_console::invisible_console;
>      Only one console can exist in a process, therefore, static is suitable. */
>   static struct fhandler_base::rabuf_t con_ra;
>   
> +/* Write pending buffer for ESC sequence handling
> +   in xterm compatible mode */
> +#define WPBUF_LEN 256
> +static unsigned char wpbuf[WPBUF_LEN];
> +static int wpixput;
> +#define wpbuf_put(x) \
> +  wpbuf[wpixput++] = x; \
> +  if (wpixput > WPBUF_LEN) \
> +    wpixput--;
> +
>   static void
>   beep ()
[...]
> +		}
> +	      else
> +		wpbuf_put (*src);
> +	      WriteConsoleA (get_output_handle (), wpbuf, wpixput, &n, 0);
> +	      con.state = normal;
> +	      wpixput = 0;
> +	    }

This generates a (useful!) warning with gcc 9.2.0:

> ../../../../winsup/cygwin/fhandler_console.cc: In member function 'virtual ssize_t fhandler_console::write(const void*, size_t)':
> ../../../../winsup/cygwin/fhandler_console.cc:67:3: error: macro expands to multiple statements [-Werror=multistatement-macros]
>    67 |   wpbuf[wpixput++] = x; \
>       |   ^~~~~
> ../../../../winsup/cygwin/fhandler_console.cc:67:3: note: in definition of macro 'wpbuf_put'
>    67 |   wpbuf[wpixput++] = x; \
>       |   ^~~~~
> ../../../../winsup/cygwin/fhandler_console.cc:2993:8: note: some parts of macro expansion are not guarded by this 'else' clause
>  2993 |        else
>       |        ^~~~

So I think either the macro need it contents contained by a 'do { ... } 
while(0)',  or that instance of it needs to be surrounded by braces, to 
do what you intend.