[bug] FMT missing builddirs for the component

Environment Details

• os: Ubuntu 22.04
• gcc version: 11.2
• conan version: 1.51.1
• python version: 3.10.4

Steps to reproduce

In an empty directory create a conanfile.txt with the following content:

[requires]
fmt/8.1.1

[generators]
cmake_paths

Issue conan install . and inspect conan_paths.cmake:

set(CONAN_FMT_ROOT "<path_to_conan_cache>/fmt/8.1.1/_/_/package/3bb43d390932310d9ef00e9986e41f02509d79e8")
set(CMAKE_MODULE_PATH  ${CMAKE_MODULE_PATH} ${CMAKE_CURRENT_LIST_DIR})
set(CMAKE_PREFIX_PATH  ${CMAKE_PREFIX_PATH} ${CMAKE_CURRENT_LIST_DIR})

Expectation: CMAKE_MODULE_PATH and CMAKE_PREFIX_PATH contain the value of CONAN_FMT_ROOT Actual: Neither variable contains the value of CONAN_FMT_ROOT.

Possible cause

The cmake_paths generator generates the CMAKE_* variables by concatenating the build_paths arrays of the dependencies. The default value for this path (which would be the correct value here) is overriden in _call_package_info in conans/client/installer.py if hasattr(conanfile, "layout") is true.

The correct value is set in conan/client/installer.py:659:

conanfile.cpp_info = CppInfo(conanfile.name, package_folder)

But it is later overridden in conan/client/installer.py:679:

if hasattr(conanfile, "layout"):
    # Old cpp info without defaults (the defaults are in the new one)
    conanfile.cpp_info = CppInfo(conanfile.name, package_folder,
                                 default_values=CppInfoDefaultValues())

[lasote]

IMHO the documentation isn’t wrong. What was documented aligned with our expectations and observations even if the implementation had different (but then compatible) semantics. The change in behavior actually breaks reasonable expectations that recipe authors may have after reading the docs.

That is True but the code of the cmake_paths never managed the root folder of the packages. That is a collateral effect of having a builddir declared in the dependencies pointing to ..

As a side-note: There is no clear indication in the docs that the cmake_paths generator is not maintained anymore. After reading the note on https://docs.conan.io/en/latest/integrations/build_system/cmake.html I expected a deprecation in the future but only after conan.tools.cmake became stable.

That is also True, but FYI we stopped long ago to develop Conan 1.X since we are working with 2.X beta.

Anyway I’ve talked with the team and we will “fix” the cmake_paths generator to add the root folders of the dependencies always because we understand this is breaking just because the dependencies are introducing the layout() method.

[SpaceIm]

@lasote Context is a project that relies on CMAKE_MODULE_PATH to find its dependencies.

CMAKE_PREFIX_PATH I guess. root package folder of fmt in CMAKE_MODULE_PATH is useless since there is no cmake module file. CMAKE_MODULE_PATH is not used at all in commands like find_file, find_program, find_library etc.