[libcamera-devel] [PATCH] gstreamer: Fix unused variable error

[Laurent Pinchart]

Hi Jaslo,

Thank you for sending a quick fix, much appreciated.

On Wed, Nov 22, 2023 at 08:15:47PM +0100, Jaslo Ziska via libcamera-devel wrote:
> Fix unused variable error introduced in fd84180d.

Missing Signed-off-by: tag. A Fixes: tag is also needed. The commit
message could read

--------
Commit fd84180d7a09 ("gstreamer: Implement element EOS handling") has
introduced a compilation warning with clang:

../../src/gstreamer/gstlibcamerasrc.cpp:768:23: error: unused variable 'oldEvent' [-Werror,-Wunused-variable]
                g_autoptr(GstEvent) oldEvent = self->pending_eos.exchange(event);
                                    ^

This seems to be a false positive, but nonetheless breaks the build. Fix
it.

Fixes: fd84180d7a09 ("gstreamer: Implement element EOS handling")
Signed-off-by: Jaslo Ziska <jaslo at ziska.de>
--------

> ---
> This patch fixes the unused variable error raised by Laurent.
> 
>  src/gstreamer/gstlibcamerasrc.cpp | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
> index 767017db..b0eb2dd7 100644
> --- a/src/gstreamer/gstlibcamerasrc.cpp
> +++ b/src/gstreamer/gstlibcamerasrc.cpp
> @@ -765,7 +765,7 @@ gst_libcamera_src_send_event(GstElement *element, GstEvent *event)
> 
>  	switch (GST_EVENT_TYPE(event)) {
>  	case GST_EVENT_EOS: {
> -		g_autoptr(GstEvent) oldEvent = self->pending_eos.exchange(event);
> +		[[maybe_unused]] g_autoptr(GstEvent) oldEvent = self->pending_eos.exchange(event);

I prefer Nicolas' proposal:

		GstEvent *oldEvent = self->pending_eos.exchange(event);
		gst_clear_event(&oldEvent);

This is more explicit, I'm slightly worried that the [[maybe_unused]]
may lead to an incorrect optimization with clang. If clang believes that
the variable is unused, it may just omit it and fail to handle the
cleanup.

I'll send a v2 of this (keeping your authorship of course). Please let
me know if you're fine with the changes by reviewing v2, and I'll push
the fix.

I also apologize for the long mail threads and the conflicted revert
that was posted, there's been some miscommunication.

> 
>  		ret = TRUE;
>  		break;

-- 
Regards,

Laurent Pinchart