Kiln - A CMake-compatible build system without stale cache

Kiln takes your existing CMakeLists.txt runs it and builds the project. No more stale cache, modern semantics, faster configuration.

Install github.com/marty1885/kiln Read the writeup

01An actual build system

Configuration, dependency resolution, and execution in one go. New files in a globbed directory get picked up because the configuration is the build.

02CMake compatiblity

Reads your existing CMakeLists.txt and runs CMake’s own Find*.cmake modules. Your projects keeps on working as-is.

03Cross-project parallelism

External projects (FetchContent, ExternalProject, CPM) get configured in-process and merged into the parent graph. Parallel builds across project boundaries. With proactive missing dependency tracking. No more magic missing object files.

04Built-in debugger

Step through CMake from a GDB-style prompt. kiln_dump_target_info prints fully-resolved properties for any target. Tools that save hours running around with educated guesses.

Catch Bugs Early

Because debugging is harder than writing code.

warning: Unbalanced generator expression (missing closing '>')
  --> /home/me/mariadb-server/cmake/install_macros.cmake:291:7
       |
   291 |       $<$<BOOL:${VCPKG_INSTALLED_DIR}>:${VCPKG_INSTALLED_DIR}/${VCPKG_TARGET_TRIPLET}/bin
       |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: Accepting as-is - CMake treats generator expressions as strings at parse time.

Kiln treats your build system as a real program. With errors reporting exact cause and location. Ledgable, helpful and actionable.

# CMake
CMake Error at cmake/modules.cmake:11 (_validate_dependency):
  Unknown CMake command "_validate_dependency".
Call Stack (most recent call first):
  cmake/modules.cmake:6 (_link_module_dependencies)
  CMakeLists.txt:6 (add_module)
# Kiln
error: Unknown command: _validate_dependency
  --> /home/me/Documents/some_project/cmake/modules.cmake:11:9
      |
   11 |         _validate_dependency(${dep})
      |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Call Stack (most recent call first):
  /home/me/some_project/cmake/modules.cmake:10 (foreach)
  /home/me/some_project/cmake/modules.cmake:6 (_link_module_dependencies)
  /home/me/some_project/CMakeLists.txt:6 (add_module)
Error: Interpretation error

And it even watches for side effects.

warning: custom_command rule for 'tvision-test-passed' exited 0 but did not create its declared OUTPUT
         declared OUTPUT: /home/me/tvision/build/debug/test/tvision-test-passed
         working dir:     /home/me/tvision/build/debug
         downstream rules depending on this OUTPUT may fail, and this
         rule will re-run on every build since its OUTPUT never appears.
         commands run:
           $ /home/me/tvision/build/debug/test/tvision-test
           $ kiln -E touch tvision-test-passed

Performance

Because time-to-beginning-of-build is also very important.

Interpreter Performance

Benchmark	CMake	Kiln	Speedup
8 queens	0.649s	0.058s	11.1x
Knight's tour (N=35)	0.446s	0.047s	8.4x
Smith Waterman (len=70)	3.629s	0.181s	20.04x
Levenshtein Distance (len=70)	3.56s	0.177s	20.1x
cmake-raytracer (256x256, 32T)	8.68s	1.21s	7.17x

Configuration Performance

Project	CMake	Kiln	Speedup
Cold LLVM configuration	8.2s	4.17s	2.01x
Warm LLVM reconfig¹	2.2s	0.55s	4.0x
Cold CMake configuration²	21.6s	11.7s	1.84x
Warm CMake reconfig^{1 2}	0.6s	0.28s	2.14x

Real world build performance³

Project	CMake + Ninja	CMake + Make	Kiln
aifoundry-org/et-platform	-	73.85s	57.41s
mariadb-server	160.52s	168.60s	156.21s

Measured on Linux with CMake 4.3.2 and Kiln 0.1.0.
¹ Apples-to-oranges: CMake’s warm path is backed by CMakeCache.txt, which memoizes find_package results and caches variables. Kiln caches lower - file lookups by mtime, glob with agressive invalidation, etc.. - so it bypasses CMake modules’ built-in short-circuit paths and re-runs more work.
² The CMake project itself. Does not include CMake generating build files (configuration only).
³ Build performance compared with release builds. Methodology is as expected: point each tool at the target repository, configure, build and sum the wall-clock time. Build time is dominated by compilation with difference down to build system overhead and efficiency.

Try it.

Build from source, then point Kiln at any directory containing a CMakeLists.txt.

→ Source on GitHub → Issue tracker → Design writeup

# Build Kiln
$ git clone https://github.com/marty1885/kiln
$ cd kiln
$ cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
$ cmake --build build

# Run it on a project
$ build/kiln -C . --config release
   Compiling  [kiln] CMakeArray.cpp
   Compiling  [kiln] ast_cache.cpp
   Compiling  [kiln] autogen.cpp
   ...
    Finished    build in 12.42s (critical path: 8.7s)

What works, what doesn’t, yet.

Kiln is early software. Most projects you point it at on Linux compile and link correctly. Plenty of things needs more work.

Working today

GCC/Clang on Linux, C, C++ and ASM
Linker selection
Incremental builds, dependency tracking, install-to-prefix
FetchContent, ExternalProject, CPM
AUTOMOC / UIC / RCC
Interactive debugger and Chrome-trace profiler
Builds tested against LLVM, Qt6Core, TBB, Folly, POCO, DuckDB, MariaDB, drogon, libzmq, Vorbis, Opus, jsoncpp, and CMake itself. With CMake 4.3.2's modules.

In progress / planned

Full CMake property set support
Windows / MSVC support
FreeBSD support
macOS support
Cross-compilation
CUDA, HIP, Objective-C, Fortran, ISPC, Java support
CPack. Not supported. install to a prefix works; producing .deb, .rpm, .dmg, .msi, etc. does not.
Unity builds
C++ module support
CMake compatibility. Always a moving target. Real projects builds; corner cases of the language and rare modules will hit edges. Please file issues.