[question] Why does CMakeToolchain's cache_variables convert recipe options to CMake bool but variables converts them to strings?

[tgurriet]

What is your question?

Hello,

While exploring the files generated by the CMakeToolchain generator, I realized that when assigning an option to cache_variables, it resulted in a CMake boolean variable in the CMakePresets.json, wherease passing the same option to variables generated a CMake string variable in the conan_toolchain.cmake.

Is there a reason for that difference? I couldn't find anything in the doc about this.

The recipe:

from conan import ConanFile
from conan.tools.cmake import CMakeDeps, CMakeToolchain, cmake_layout

class helloRecipe(ConanFile):
    name = "my_lib"
    version = "1.0"

    settings = "os", "compiler", "build_type", "arch"
    options = {"option": [True, False]}
    default_options = {"option": True}
    exports_sources = "CMakeLists.txt", "src/*", "include/*"

    def layout(self):
        cmake_layout(self)

    def generate(self):
        dep = CMakeDeps(self)
        dep.generate()

        tc = CMakeToolchain(self)
        tc.variables["option"] = self.options.get_safe("option")
        tc.cache_variables["option"] = self.options.get_safe("option")
        tc.variables["option2"] = self.options.option
        tc.cache_variables["option2"] = self.options.option
        tc.variables["option3"] = True
        tc.cache_variables["option3"] = True
        tc.generate()

The generated CMakePresets.json:

...
"cacheVariables": {
  "option": "ON",
  "option2": "ON",
  "option3": "ON",
  "CMAKE_POLICY_DEFAULT_CMP0091": "NEW",
  "CMAKE_BUILD_TYPE": "Debug"
},
...

The generated conan_toolchain.cmake:

...
# Variables
set(option "True" CACHE STRING "Variable option conan-toolchain defined")
set(option2 "True" CACHE STRING "Variable option2 conan-toolchain defined")
set(option3 ON CACHE BOOL "Variable option3 conan-toolchain defined")
...

Have you read the CONTRIBUTING guide?

• I've read the CONTRIBUTING guide

[tgurriet]

@memsharded Should I generate a bug report with more info maybe?

[franramirez688]

Hi, @tgurriet - Thanks a lot for the report.

Yes, this is known. CMakeToolchain has a mechanism to convert raw options for the cache_variables attribute, but not for the variables one.
Let me discuss with the team this issue to see which would be the best approach.

[tgurriet]

Sounds good, thanks!

[memsharded]

We have been checking this:

• yes, there are some small differences in how variables and cache_variables are managed
• This are mostly historical differences
• We have considered trying to align a bit more the behavior, but it seems it would be breaking, so most likely not worth it.

The solution to make them behave similar would be to force the bool() type for variables when desired.

I am closing this ticket as responded, but please re-open or create a new one for any further question.