[feature] CMakeToolchain cacheVariables should have a type

[jmarrec]

What is your suggestion?

Type mismatch in CMake configure arguments is a common issue that is really hard to track down, and as such I'm really pedantic about specifying the type of the variables when configuring CMake, especially for path/filepath ones.

--DMY_FLAG=ON
+-DMY_FLAG:BOOL=ON

-DMY_PATH=/path/to/file
+DMY_PATH:FILEPATH=/path/to/file

-DMY_DIR_PATH=/path/to/dir
+DMY_DIR_PATH:PATH=/path/to/dir

I noticed that the CMake presets do not hold a type for cacheVariables, while the CMake documentation explicitly says it can be a value, or a an object with both type and value, cf https://cmake.org/cmake/help/v3.29/manual/cmake-presets.7.html#configure-preset

Perhaps should consider explictly setting it, around

conan/conan/tools/cmake/toolchain/toolchain.py

Lines 240 to 271 in f1ef6e4

	cache_variables = {}
	for name, value in self.cache_variables.items():
	if isinstance(value, bool):
	cache_variables[name] = "ON" if value else "OFF"
	elif isinstance(value, _PackageOption):
	if str(value).lower() in ["true", "false", "none"]:
	cache_variables[name] = "ON" if bool(value) else "OFF"
	elif str(value).isdigit():
	cache_variables[name] = int(value)
	else:
	cache_variables[name] = str(value)
	else:
	cache_variables[name] = value
	buildenv, runenv, cmake_executable = None, None, None
	if self._conanfile.conf.get("tools.cmake.cmaketoolchain:presets_environment", default="",
	check_type=str, choices=("disabled", "")) != "disabled":
	build_env = self.presets_build_environment.vars(self._conanfile) if self.presets_build_environment else VirtualBuildEnv(self._conanfile, auto_generate=True).vars()
	run_env = self.presets_run_environment.vars(self._conanfile) if self.presets_run_environment else VirtualRunEnv(self._conanfile, auto_generate=True).vars()
	buildenv = {name: value for name, value in
	build_env.items(variable_reference="$penv{{{name}}}")}
	runenv = {name: value for name, value in
	run_env.items(variable_reference="$penv{{{name}}}")}
	cmake_executable = self._conanfile.conf.get("tools.cmake:cmake_program", None) or self._find_cmake_exe()
	write_cmake_presets(self._conanfile, toolchain, self.generator, cache_variables,
	self.user_presets_path, self.presets_prefix, buildenv, runenv,
	cmake_executable)

Related:

• [question] Why does CMakeToolchain's cache_variables convert recipe options to CMake bool but variables converts them to strings? #14590
• [question] cacheVariables data type mismatch in generated CMakePresets.json #14568

---

Quoting Professional CMake - Practical Guide, 15th edition by Craig Scott (I hope that's ok, since I can already find the same online at https://discourse.cmake.org/t/cmake-d-var-type-value/1135)

There is a special case for handling values initially declared without a type on the cmake command
line. If the project’s CMakeLists.txt file then tries to set the same cache variable and specifies a type
of FILEPATH or PATH , then if the value of that cache variable is a relative path, CMake will treat it as
being relative to the directory from which cmake was invoked and automatically convert it to an
absolute path. This is not particularly robust, since cmake could be invoked from any directory, not
just the build directory. Therefore, developers are advised to always include a type if specifying a
variable on the cmake command line for a variable that represents some kind of path.

It is a good habit to always specify the type of the variable on the command line in general anyway so that it is
likely to be shown in GUI applications in the most appropriate form. It will also prevent one of the
surprising behavior scenarios mentioned in the previous section

Have you read the CONTRIBUTING guide?

• I've read the CONTRIBUTING guide

[memsharded]

Closing after #16079 is closed