cmake: include path for ggml.h not exported if GGML_BACKEND_DL is set

[SchaichAlonso]

Description

Projects consuming ggml use find_package(ggml) in order to import the ggml::ggml target, which results in the installed version of cmake/ggml-config.cmake.in being processed by cmake.

In order to be able to consume ggml, comsumer source files #include <ggml.h>, which requires the ggml.h to be within an include path passed to the compiler. ggml-config.cmake assures the corresponding path to be passed to the compiler by assigning this path to the INTERFACE_INCLUDE_DIRECTORY cmake property for each installed backend in line 141 of the v0.10.0 version of the file, and each backend is then assigned to the ggml::ggml target in lines 175, 179 and 180.

If, however, the GGML_BACKEND_DL option was enabled when building ggml, lines 143 and 175 will not be processed over the condition in line 128, resulting in ggml::ggml being only ggml::ggml-base, which does not have an INTERFACE_INCLUDE_DIRECTORY property assigned to it.

Expectation

A third party project that was able to import ggml::ggml via find_package(ggml) should be able to use the ggml.h header file without having to search for it explicitly, even if ggml was not installed into a system directory. cmake handles the details as long as it can discover ggml-config.cmake on the system.

Solution

Assign the INTERFACE_INCLUDE_DIRECTORY property to ggml::ggml-base within a context that is independend on GGML_BACKEND_DL.

[SchaichAlonso]

The include path should be assigned to ggml::ggml rather then ggml::ggml-base, because the header files are a PUBLIC_HEADER property of ggml rather then ggml-base.

[ggerganov]

Doesn't this already set the include path for both ggml and ggml-base?

ggml/src/CMakeLists.txt

Lines 466 to 469 in 8be60f8

	foreach (target ggml-base ggml)
	target_include_directories(${target} PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/../include> $<INSTALL_INTERFACE:include>)
	target_compile_features (${target} PRIVATE c_std_11 cxx_std_17) # don't bump
	endforeach()

[SchaichAlonso]

Thanks for investigating into this issue. The INSTALL_INTERFACE include directory property is a target property that is supposed to do just that.

However, the ggml::ggml target imported by consuming projects that use find_package(ggml) is not the ggml::ggml target defined in of the src/CMakeLists.txt file ...

ggml/src/CMakeLists.txt

Lines 225 to 228 in 8be60f8

	add_library(ggml
	ggml-backend-dl.cpp
	ggml-backend-reg.cpp)
	add_library(ggml::ggml ALIAS ggml)

... but instead is an unrelated target that has the same name, and is defined in cmake/ggml-config.cmake(.in) ...

ggml/cmake/ggml-config.cmake.in

Lines 112 to 115 in 8be60f8

	add_library(ggml::ggml UNKNOWN IMPORTED)
	set_target_properties(ggml::ggml
	PROPERTIES
	IMPORTED_LOCATION "${GGML_LIBRARY}")

---

CMake has the ability to "export" a target, using install(EXPORT), which generates a snippet for ggml-config.cmake that contains the ggml::ggml target definition of the ggml project (src/CMakeLists.txt), along with all properties assigned to it. Once the target definition was exported, it can be include()-ed by ggml-config.cmake (.in), replacing the ggml::ggml definition there by the definition that was generated by install(EXPORT).

I can prepare a patch to export the ggml targets from src/CMakeLists.txt and modify cmake/ggml-config.cmake.in to import the export targets definitions, either into ggml-org/llama.cpp#22482 or by making a PR here (the PR template for the ggml project proposes to open PRs at llama-cpp rather then here)

[ggerganov]

Thanks. Please update ggml-org/llama.cpp#22482 as you think it should be and after we merge it, we'll propagate the change to this repo.