``` $ cat CMakeLists.txt cmake_minimum_required(VERSION 3.28) project(ProjectName) add_library(objectlib OBJECT /dev/null) set_target_properties(objectlib PROPERTIES LINKER_LANGUAGE CXX) add_library(lib empty.cc) add_dependencies(lib objectlib) $ echo > empty.cc $ cmake -G Ninja . [ ... ] $ samu samu: file is missing and not created by any action: 'CMakeFiles/objectlib.dir' $ ls -l CMakeFiles/objectlib.dir ls: cannot access 'CMakeFiles/objectlib.dir': No such file or directory $ grep CMakeFiles/objectlib.dir build.ninja build cmake_object_order_depends_target_objectlib: phony || CMakeFiles/objectlib.dir $ rm -r CMakeCache.txt CMakeFiles $ sed -i -e 's:/dev/null:empty.cc:' CMakeLists.txt $ cmake -G Ninja . [ ... ] $ ls -al CMakeFiles/objectlib.dir total 0 drwxr-xr-x 2 alex alex 40 Dec 20 17:15 . drwxr-xr-x 7 alex alex 220 Dec 20 17:15 .. $ samu [1/3] Building CXX object CMakeFiles/lib.dir/empty.cc.o [2/3] Building CXX object CMakeFiles/objectlib.dir/empty.cc.o [3/3] Linking CXX static library liblib.a $ cmake --version cmake version 3.28.1 CMake suite maintained and supported by Kitware (kitware.com/cmake). $ samu --version 1.9 ``` It appears that CMake skips creating object directories if no files are planned to be put there, but still adds an order-only dependency. The ninja documentation does not specify the behavior if order-only dependencies don't exist and can't be made; the reference implementation ignores it, but samurai issues an error. I would argue this is a bug in CMake, not samurai, for several reasons: 1. The order-only dependency is actually built if a rule exists. "order-only" refers to the behavior when the dependency exists but is newer than the target, not the behavior when it doesn't exist. 2. As far as I can tell, unbuildable order-only dependencies are useless. 3. Order-only dependencies (probably) come from GNU make, which also issues an error: ``` $ cat Makefile b: | a $ make make: *** No rule to make target 'a', needed by 'b'. Stop. $ make --version GNU Make 4.4.1 ``` By my reckoning, CMake shouldn't emit order-only dependencies without a rule to create the dependency.