Targets using only target_sources don't get sanitizer flags

[GHF]

With CMake 3.13, I've been writing a bunch of targets like this, where the SOURCES property of a target can be added by subdirectories and its evaluation is deferred to "generation time."

add_executable(myexecutable)
target_sources(myexecutable PRIVATE main.cc)

Unfortunately, this makes these targets incompatible with add_sanitizers(...) because the scripts are not able to find any source files in the target:

CMake Warning at third_party/sanitizers-cmake/cmake/FindSanitizers.cmake:82 (message):
  Sanitizers for target myexecutable may not be usable, because it uses no or an
  unknown compiler.  This is a false warning for targets using only object
  lib(s) as input.
Call Stack (most recent call first):
  CMakeLists.txt:35 (add_sanitizers)

I'm pretty new to "modern" CMake and I don't know how to get around this. Maybe the compiler flags added by sanitizer_add_flags need to be generator expressions that get evaluated at generation time?

[saxbophone]

Hmmm, interesting —I wonder if this same issue might be why I can't seem to get the sanitisers provided by this package to fail my CI builds? saxbophone/arby#153

I am also using target_sources(), although IIRC I'm not getting a build warning or error, and when compiling it does appear to be using libasan/ubsan, but I can't seem to deliberately fail the build by introducing undefined behaviour into my code:

int k = 0x7fffffff;
k += 1; // cause integer overflow

which makes this pretty useless for actually detecting any UB...