Return values from external library calls are not always checked.

[tarek-y-ismail]

In our codebase, return values from external libraries are not always checked. For return codes, this can manifest as issues later during execution that require careful debugging to track down the cause of. For return values as pointers, this can manifest itself as segfaults.

The following calls have been identified, though this isn't an exhaustive list:

• xkb_state_key_get_utf8
• xkb_compose_table_new_from_locale
• eglBindAPI, eglDestroyImageKHR, eglDebugMessageControlKHR, eglDestroyContext, eglDestroySurface and friends
• pixman_image_create_bits, pixman_transform_scale, pixman_image_set_transform, pixman_image_set_filter
• udev_enumerate_scan_devices, udev_monitor_enable_receiving, udev_monitor_filter_add_match_subsystem_devtype, udev_device_get_action
• drmGetCap

For most of these, printing something should be enough. Though for others more work may be needed.

In addition to plugging the holes we currently have, it would be nice to have some code analysis tool (TICS?) to give us a list of all calls where we don't use/check the return value.

[tarek-y-ismail]

Depending on how much work each library's calls will need, this may be split into separate issues.

[tarek-y-ismail]

So it turns out that clang-tidy can check for unused returns!

run-clang-tidy-21 -header-filter=.* -p <build_dir_with_compile_commands>/ -checks='-*,bugprone-unused-return-value' -config="{CheckOptions: [{key: bugprone-unused-return-value.CheckedFunctions, value: '::.*'}]}" 2>&1 > unchecked-function-returns.txt

Which can be further filtered:

sed -n 's/^\(.*\): warning:.*\[bugprone-unused-return-value\]$/\1/p' unchecked-function-returns.txt

Attached is the 3000+ lines of output that yields.

unchecked-function-returns-filtered.txt

Now we just need to sift through them and figure out which need to be explicitly handled.

[tarek-y-ismail]

I don't think copilot saw the comment...