initialize variables in wlr_surface.c

[ppascher]

This fixes the following warnings/errors with -Werror set (default):

ninja: Entering directory `build'
[26/47] Compiling C object libwlroots.so.7.p/types_wlr_surface.c.o
FAILED: libwlroots.so.7.p/types_wlr_surface.c.o
cc -Ilibwlroots.so.7.p -I. -I.. -Iinclude -I../include -Iprotocol -I../protocol -I/usr/include/libdrm -I/usr/include/pixman-1 -I/usr/include/uuid -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -std=c11 -O3 -DWLR_USE_UNSTABLE -Wundef -Wlogical-op -Wmissing-include-dirs -Wold-style-definition -Wpointer-arith -Winit-self -Wstrict-prototypes -Wimplicit-fallthrough=2 -Wendif-labels -Wstrict-aliasing=2 -Woverflow -Wmissing-prototypes -Wno-missing-braces -Wno-missing-field-initializers -Wno-unused-parameter -fmacro-prefix-map=../= -DHAS_LIBUUID=1 '-DICONDIR="/usr/share/icons"' -fPIC -MD -MQ libwlroots.so.7.p/types_wlr_surface.c.o -MF libwlroots.so.7.p/types_wlr_surface.c.o.d -o libwlroots.so.7.p/types_wlr_surface.c.o -c ../types/wlr_surface.c
../types/wlr_surface.c: In function ‘surface_commit_pending’:
../types/wlr_surface.c:235:55: error: ‘src_width’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  235 |    float scale_x = (float)pending->viewport.dst_width / src_width;
      |                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
../types/wlr_surface.c:233:8: note: ‘src_width’ was declared here
  233 |    int src_width, src_height;
      |        ^~~~~~~~~
../types/wlr_surface.c:236:56: error: ‘src_height’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  236 |    float scale_y = (float)pending->viewport.dst_height / src_height;
      |                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
../types/wlr_surface.c:233:19: note: ‘src_height’ was declared here
  233 |    int src_width, src_height;
      |                   ^~~~~~~~~~
../types/wlr_surface.c: In function ‘wlr_surface_get_effective_damage’:
../types/wlr_surface.c:1293:62: error: ‘src_width’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
 1293 |   float scale_x = (float)surface->current.viewport.dst_width / src_width;
      |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
../types/wlr_surface.c:1294:63: error: ‘src_height’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
 1294 |   float scale_y = (float)surface->current.viewport.dst_height / src_height;
      |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
cc1: all warnings being treated as errors
ninja: build stopped: subcommand failed.

[ppascher]

Maybe it is not a good idea to initialize to 0?

[emersion]

Hm, this will just cause a division by zero in case the buffer size is not divisible by the scale.

I wonder if we should keep the scale check in surface_state_viewport_src_size. Maybe we should move it out of the function into surface_state_finalize.

[ppascher]

I wonder if we should keep the scale check in surface_state_viewport_src_size. Maybe we should move it out of the function into surface_state_finalize.

This would have to be answered by someone else I am afraid as I do not know how it all fits together.

[gnzlbg]

This is preventing wlroots-git from building in the AUR.

FWIW I think the warning is just wrong here, initializing these variables is pointless, and one should disable the warning, e.g., by using the proper pragma to turn it off locally here.

Because of warnings with false-positives / incorrect diagnostics, it makes little sense to use -Werror as a default for everybody.

I think -Werror should be optional, and instead CI should always turn it on to catch these things.

[gnzlbg]

If you want to initialize this variables to something, initialize them to some invalid value, e.g., 0 or -1, and after calling the API, check that this value has changed.

[emersion]

I think -Werror should be optional, and instead CI should always turn it on to catch these things.

NACK. See https://github.com/swaywm/wlroots/wiki/Packaging-recommendations.

[emersion]

See the first commit in #2742.

[ppascher]

fixed with #2742