[question] `CMakeDeps` failed on header only libs

conanfile.py

requires = ["rapidjson/cci.20200410"]
generators = ["CMakeDeps", "CMakeToolchain"]

$ conan create .
...
ERROR: Error in generator 'CMakeDeps': 'settings.build_type' doesn't exist

Does it mean that CMakeDeps can not be used if any lib in requires has no build_type settings?

conafile.py for rapidjson

from conans import ConanFile, tools
import os

required_conan_version = ">=1.33.0"


class RapidjsonConan(ConanFile):
    name = "rapidjson"
    description = "A fast JSON parser/generator for C++ with both SAX/DOM style API"
    topics = ("conan", "rapidjson", "json", "parser", "generator")
    url = "https://github.com/conan-io/conan-center-index"
    homepage = "http://rapidjson.org"
    license = "MIT"
    no_copy_source = True

    @property
    def _source_subfolder(self):
        return "source_subfolder"

    def source(self):
       tools.get(**self.conan_data["sources"][self.version], strip_root=True, destination=self._source_subfolder)

    def package(self):
        self.copy(pattern="license.txt", dst="licenses", src=self._source_subfolder)
        self.copy(pattern="*", dst="include", src=os.path.join(self._source_subfolder, "include"))

    def package_id(self):
        self.info.header_only()

    def package_info(self):
        self.cpp_info.names["cmake_find_package"] = "RapidJSON"
        self.cpp_info.names["cmake_find_package_multi"] = "RapidJSON"

[czoido]

But why a header only lib needs settings = "build_type", this will lead to duplication of the lib in local conan cache unnecessarily, right?

The lib will not be duplicated because it does not have the build_type setting, it’s deleted because it’s a header only and will have only one package_id, please read more about this here: https://docs.conan.io/en/latest/howtos/header_only.html

BTW, after fixing #9611, I have tried to delete settings = "build_type" and do conan create ., it succeeds. It is not necessary, isn’t it?

That’s because you are using cmake_find_package generator there and will not need it.

[czoido]

Hi @playgithub, As I said, you have to add at least the build_type setting to the conanfile. The CMakeDeps generator needs that setting information. So please add: settings = "build_type" to the consumer’s conanfile like this:

class CppjiebaConan(ConanFile):
    settings = "build_type"
    ...

Some other conan generators may not need this setting.