[bug] Profile's compiler.cppstd not respected when installing package

[pierricgimmig]

Describe the bug

I'm trying to install the abseil package, I'm hoping that my default profile's compiler.cppstd=17 will be respected, but it's not.

Running conan install . -of build --build=missing

gives me:

======== Computing necessary packages ========
abseil/20240116.2: Main binary package 'dee9f7f985eb1c20e3c41afaa8c35e2a34b5ae0b' missing
abseil/20240116.2: Checking 3 compatible configurations
abseil/20240116.2: Found compatible package '9bdee485ef71c14ac5f8a657202632bdb8b4482b': compiler.cppstd=14
Requirements
    abseil/20240116.2#54f81a20ccd26a6558e18d57059847e2:9bdee485ef71c14ac5f8a657202632bdb8b4482b#90b35a9d741f2b46ef5bd2f5ce7516f2 - Cache

It seems that an abseil package with compiler.cppstd=14 is chosen. I would have expected abseil to compile from source using my specified compiler.cppstd=17 instead, is this expected? I need cpp 17 so that abseil compiles with std::string_view support. The code below won't compile without it. Thanks for your help.

Windows 11, conan 2.8.1

C:\Users\pierr\git\conan_abseil (main)
λ conan profile show
Host profile:
[settings]
arch=x86_64
build_type=Release
compiler=msvc
compiler.cppstd=17
compiler.runtime=dynamic
compiler.runtime_type=Release
compiler.version=193
os=Windows

Build profile:
[settings]
arch=x86_64
build_type=Release
compiler=msvc
compiler.cppstd=17
compiler.runtime=dynamic
compiler.runtime_type=Release
compiler.version=193
os=Windows

How to reproduce it

CMakeLists.txt

cmake_minimum_required(VERSION 3.15)
project(compressor CXX)

# Set C++17 standard
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(absl REQUIRED)

add_executable(${PROJECT_NAME} main.cpp)
target_link_libraries(${PROJECT_NAME} abseil::abseil)

conanfile.txt

[requires]
abseil/20240116.2

[generators]
CMakeDeps
CMakeToolchain

main.cpp

#include <iostream>
#include <string.h>
#include <absl/strings/str_cat.h>

void main()
{
    std::string_view blah = "blah";
    std::string message = absl::StrCat("Hello, Abseil ", blah, "!");
    std::cout << message << std::endl;
}

then run conan install . -of build --build=missing

[memsharded]

Hi @pierricgimmig

Thanks for your feedback.

This is not a bug, but intended. The default binary compatibility compatibility.py implements binary compatibility across different compiler.cppstd values, so if there is no existing binary for cppstd=17 it can fallback to an existing cppstd=14.

If you want to force the build of the cppstd=17 it is possible:

• To explicitly add a --build="abseil/*" to force the build
• To modify the default compatibility.py plugin and add exclusions there for the packages you want. Recall you can manage the compatibility.py plugin as any other user configuration with conan config install or conan config install-pkg.
• If you control the abseil recipe, (you maintain a fork of conan-center-index recipe), you can use the extension_properties to exclude it from the default cppstd binary compatibility: See https://docs.conan.io/2/reference/conanfile/attributes.html#extension-properties

Please try that and let us know.

[pierricgimmig]

Hi @memsharded , thanks for the detailed answer. Running with build="abseil/*" does indeed fix the issue, thank you!

[memsharded]

Nice, happy to help.

I am closing the ticket then as solved, but feel free to re-open or create new tickets if there are any further question or issues. Thanks for the feedback!