Build failure when `-Dgdk-pixbuf=disabled` : unused or undefined variables

[cevdetta]

When building swaylock with the gdk-pixbuf feature disabled (-Dgdk-pixbuf=disabled), the build fails due to unused or undefined variables in the code, particularly in comm.c.

It seems the build does not properly exclude code paths that depend on gdk-pixbuf or related features when the feature is turned off. This results in variables like struct sigaction sa being defined but unused, or undeclared identifiers like SIG_IGN and SIGUSR1 being referenced when their headers aren't included.

Steps to reproduce

1. Clone the repo and checkout the latest tagged release (or master).

2. Run the Meson setup with these options:

   meson setup build -Dgdk-pixbuf=disabled ...

3. Run:

   meson compile -C build

Error output

Click to expand

$ arch-meson build --buildtype=release --auto-features=disabled -Dstrip=true -Db_lto=true -Db_lto_mode=default -Db_ndebug=true -Dpam=enabled -Dgdk-pixbuf=disabled -Dman-pages=enabled -Dzsh-completions=false -Dbash-completions=true -Dfish-completions=false+ exec meson setup --prefix /usr --libexecdir lib --sbindir bin --buildtype plain --auto-features enabled --wrap-mode nodownload -D b_pie=true -D python.bytecompile=1 build --buildtype=release --auto-features=disabled -Dstrip=true -Db_lto=true -Db_lto_mode=default -Db_ndebug=true -Dpam=enabled -Dgdk-pixbuf=disabled -Dman-pages=enabled -Dzsh-completions=false -Dbash-completions=true -Dfish-completions=false

The Meson build system
Version: 1.9.1
Source dir: /home/c/web-dev/pkgbuilds-wayland/swaylock-pure/swaylock-1.8.3
Build dir: /home/c/web-dev/pkgbuilds-wayland/swaylock-pure/swaylock-1.8.3/build
Build type: native build
Project name: swaylock
Project version: 1.8.3
C compiler for the host machine: cc (gcc 15.2.1 "cc (GCC) 15.2.1 20250813")
C linker for the host machine: cc ld.bfd 2.45.0
Host machine cpu family: x86_64
Host machine cpu: x86_64
Compiler for C supports arguments -Wno-unused-parameter: YES
Compiler for C supports arguments -Wno-unused-result: YES
Compiler for C supports arguments -Wundef: YES
Compiler for C supports arguments -Wvla: YES
Found pkg-config: YES (/usr/bin/pkg-config) 2.5.1
Run-time dependency wayland-client found: YES 1.24.0
Run-time dependency wayland-protocols found: YES 1.45
Build-time dependency wayland-scanner found: YES 1.24.0
Run-time dependency xkbcommon found: YES 1.11.0
Run-time dependency cairo found: YES 1.18.4
Dependency gdk-pixbuf-2.0 skipped: feature gdk-pixbuf disabled
Library pam found: YES
Library crypt found: YES
Library m found: YES
Library rt found: YES
Program git found: YES (/usr/bin/git)
Program scdoc found: YES (/usr/bin/scdoc)
Program /usr/bin/wayland-scanner found: YES (/usr/bin/wayland-scanner)
Configuring config.h using configuration
Run-time dependency bash-completion found: YES 2.16.0
Did not find CMake 'cmake'
Found CMake: NO
Run-time dependency fish found: NO (tried pkgconfig and cmake)
Build targets in project: 2

swaylock 1.8.3

  User defined options
    auto_features     : disabled
    b_lto             : true
    b_lto_mode        : default
    b_ndebug          : true
    b_pie             : true
    bash-completions  : true
    buildtype         : release
    fish-completions  : false
    gdk-pixbuf        : disabled
    libexecdir        : lib
    man-pages         : enabled
    pam               : enabled
    prefix            : /usr
    python.bytecompile: 1
    sbindir           : bin
    strip             : true
    wrap_mode         : nodownload
    zsh-completions   : false

Found ninja-1.12.1 at /usr/bin/ninja

$ meson compile -C build/

INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /usr/bin/ninja -C /home/c/web-dev/pkgbuilds-wayland/swaylock-pure/swaylock-1.8.3/build
ninja: Entering directory `/home/c/web-dev/pkgbuilds-wayland/swaylock-pure/swaylock-1.8.3/build'
[9/18] Compiling C object swaylock.p/comm.c.o
FAILED: swaylock.p/comm.c.o
cc -Iswaylock.p -I. -I.. -Iinclude -I../include -I/usr/include/cairo -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/pixman-1 -flto=auto -fdiagnostics-color=always -DNDEBUG -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -std=c11 -O3 -D_POSIX_C_SOURCE=200809L -Wno-unused-parameter -Wno-unused-result -Wundef -Wvla -fPIE -DWITH_GZFILEOP -MD -MQ swaylock.p/comm.c.o -MF swaylock.p/comm.c.o.d -o swaylock.p/comm.c.o -c ../comm.c
../comm.c: In function ‘spawn_comm_child’:
../comm.c:99:24: error: variable ‘sa’ has initializer but incomplete type
   99 |                 struct sigaction sa = {
      |                        ^~~~~~~~~
../comm.c:100:26: error: ‘struct sigaction’ has no member named ‘sa_handler’
  100 |                         .sa_handler = SIG_IGN,
      |                          ^~~~~~~~~~
../comm.c:100:39: error: ‘SIG_IGN’ undeclared (first use in this function)
  100 |                         .sa_handler = SIG_IGN,
      |                                       ^~~~~~~
../comm.c:100:39: note: each undeclared identifier is reported only once for each function it appears in
../comm.c:100:39: error: excess elements in struct initializer [-Werror]
../comm.c:100:39: note: (near initialization for ‘sa’)
../comm.c:99:34: error: storage size of ‘sa’ isn’t known
   99 |                 struct sigaction sa = {
      |                                  ^~
../comm.c:102:17: error: implicit declaration of function ‘sigaction’ [-Wimplicit-function-declaration]
  102 |                 sigaction(SIGUSR1, &sa, NULL);
      |                 ^~~~~~~~~
../comm.c:102:27: error: ‘SIGUSR1’ undeclared (first use in this function)
  102 |                 sigaction(SIGUSR1, &sa, NULL);
      |                           ^~~~~~~
../comm.c:99:34: error: unused variable ‘sa’ [-Werror=unused-variable]
   99 |                 struct sigaction sa = {
      |                                  ^~
cc1: all warnings being treated as errors
[17/18] Compiling C object swaylock.p/main.c.o
ninja: build stopped: subcommand failed.

Suggested fix

A possible fix would be to wrap the usage of struct sigaction, SIGUSR1, and related functions/macros in #ifdefs or conditionally include the required headers (e.g., <signal.h>) only if that part of the code is enabled. Alternatively, adjust the build files to exclude entire compilation units that rely on gdk-pixbuf if the feature is disabled.