[bug] OPENSSL_FOUND and similar variables aren't defined

[computerquip-work]

External code often relies on the variable OPENSSL_FOUND being defined. I see code in the OpenSSL package recipe to handle this but I'm a bit confused as to how this is supposed to work. Provided is a test case showing that OPENSSL_FOUND is not defined but OpenSSL_FOUND is defined by default.

Environment Details (include every applicable attribute)

• OS: Arch LInux
• Compiler: GCC 11.2.0
• Conan version: 1.46.0
• Python version: 3.10.2

Steps to reproduce

Test Case: https://github.com/computerquip-work/conan-openssl-fail-case

From source:

mkdir -p build;
cd build;
conan install ..;
conan build ..;

[computerquip-work]

I really don't understand this. If I minimize the example (note the use of OpenSSL 3.0):

from conans import ConanFile, RunEnvironment, tools
from conan.tools.cmake import CMake, CMakeToolchain, CMakeDeps

class FailConan(ConanFile):
    name = "fail-test-case"
    version = "0.0.1"
    license = "Apache-2.0"
    requires = ("openssl/3.0.1")
    settings = "os", "compiler", "build_type", "arch"
    description = ""

    def generate(self):
        tc = CMakeToolchain(self)
        tc.generate()

        deps = CMakeDeps(self)
        deps.generate()

    def build(self):
        cmake = CMake(self)
        cmake.configure()
        cmake.build()

I get the output:

<snip>
-- The C compiler identification is GNU 11.2.0
-- The CXX compiler identification is GNU 11.2.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Conan: Component target declared 'OpenSSL::Crypto'
-- Conan: Component target declared 'OpenSSL::SSL'
-- Conan: Target declared 'openssl::openssl'
-- Conan: Target declared 'ZLIB::ZLIB'
-- Conan: Including build module from '/home/zlund/.conan/data/openssl/3.0.1/_/_/package/b88c434d8110e892fcfb7bbb4f76234f590822f1/lib/cmake/conan-official-openssl-variables.cmake'
-- Conan: Including build module from '/home/zlund/.conan/data/openssl/3.0.1/_/_/package/b88c434d8110e892fcfb7bbb4f76234f590822f1/lib/cmake/conan-official-openssl-variables.cmake'
-- 2 The newer OpenSSL OpenSSL_FOUND is defined.
-- Configuring done
-- Generating done
-- Build files have been written to: /home/<snip>/Projects/<snip>/applications/openssl-conan-fail/build

Looking at that cmake module, it contains:

if(DEFINED OpenSSL_FOUND)
    set(OPENSSL_FOUND ${OpenSSL_FOUND})
endif()
if(DEFINED OpenSSL_INCLUDE_DIR)
    set(OPENSSL_INCLUDE_DIR ${OpenSSL_INCLUDE_DIR})
endif()
if(DEFINED OpenSSL_Crypto_LIBS)
    set(OPENSSL_CRYPTO_LIBRARY ${OpenSSL_Crypto_LIBS})
    set(OPENSSL_CRYPTO_LIBRARIES ${OpenSSL_Crypto_LIBS}
                                 ${OpenSSL_Crypto_DEPENDENCIES}
                                 ${OpenSSL_Crypto_FRAMEWORKS}
                                 ${OpenSSL_Crypto_SYSTEM_LIBS})
endif()
if(DEFINED OpenSSL_SSL_LIBS)
    set(OPENSSL_SSL_LIBRARY ${OpenSSL_SSL_LIBS})
    set(OPENSSL_SSL_LIBRARIES ${OpenSSL_SSL_LIBS}
                              ${OpenSSL_SSL_DEPENDENCIES}
                              ${OpenSSL_SSL_FRAMEWORKS}
                              ${OpenSSL_SSL_SYSTEM_LIBS})
endif()
if(DEFINED OpenSSL_LIBRARIES)
    set(OPENSSL_LIBRARIES ${OpenSSL_LIBRARIES})
endif()
if(DEFINED OpenSSL_VERSION)
    set(OPENSSL_VERSION ${OpenSSL_VERSION})
endif()

It seems like it should be set. I can modify that file to output markers. The file is definitely included but in that context if (DEFINED OpenSSL_FOUND) fails. So this seems to me that the *Config.cmake files don't implement _FOUND for some reason (does this work elsewhere?).

EDIT: After looking at some documentation, CMake automatically sets _FOUND but appears to be after the config module has finished running. So unfortunately, this particular use-case seems broken.

[computerquip-work]

I also found this related issue from a few years back: #3148

Seems that in combination with that and #10387, there's no obvious way to work around this.

After delving the source code a bit, I realized there's the concept of "blocks" described in CMakeToolchain. One of those is "find_paths" which apparently controls CMAKE_FIND_PACKAGE_PREFER_CONFIG, but unfortunately doesn't document how. This is what ultimately "fixes" the problem for me:

    def generate(self):
        tc = CMakeToolchain(self)
        tc.blocks["find_paths"].values["find_package_prefer_config"]=False
        tc.generate()

        deps = CMakeDeps(self)
        deps.generate()

Since the OpenSSL package generates a FindOpenSSL.cmake module that works (as it explicitly sets OpenSSL_FOUND before the standard variables cmake script is called), this is "good enough".

I'm leaving this open because this experience frankly sucked however.

[jngrb]

I found that conan-io/conan-center-index#12838 only fixed this for the 1.x.x recipe versions.

I made the similar fix for the 3.x.x recipe versions in conan-io/conan-center-index#14426

[hchechao2]

tc.blocks["find_paths"].values["find_package_prefer_config"]=False works for me !!!

[memsharded]

The PRs above should have taken care of this issue (in the conan-center-index repo, sorry this wasn't followed up back then) time ago.

@hchechao2 It is also possible to control the files that CMakeDeps generate via .set_property(...., "cmake_find_mode", ) property, to control specifically the files generated for each dependency if you need.

I am closing this ticket as solved time ago, please create new tickets if you have any further question, thanks!