[MesonToolchain] Added Objective-C/C++ arguments

[franramirez688]

Changelog: Feature: Added objc_args/objc_link_args/objcpp_args/objcpp_link_args to MesonToolchain for Objective-C/C++ language.
Closes: #11628
Docs: conan-io/docs#2652

[franramirez688]

I want to add another test using Objective-C++ (typical hello.lib and demo app linking with it)

[SSE4]

this is outstanding PR, it looks fantastic!

[memsharded]

This is looking good, though I wonder a bit about objectiveC support in general:

• Shouldn't it be its own compiler? Are there packages mixed with C/C++ and objC? Only ObjC?
• What happens with the binary model for objC?
• What happens with other build systems like CMake for ObjC?

[SSE4]

• Shouldn't it be its own compiler?

in which context?
if you mean compiler executable, there are just clang and clang++. there are no dedicated executables to compile Objective-C[++] code. it's basically controlled by flags (e.g. -x objective-c)
if you mean compiler as a suite, it's part of LLVM/Clang package.
if you mean compiler as a conan setting, it is just apple-clang entry.

• Are there packages mixed with C/C++ and objC? Only ObjC?

there are MANY packages mixing C/C++ with Objective-C/Objective-C++.
Objective-C[++] basically acts as a glue for al the modern Apple APIs - there is just no way to invoke these APIs from C/C++.

• What happens with the binary model for objC?

it's basically follows pure C model more or less. we didn't need to complicate it in the past.

• What happens with other build systems like CMake for ObjC?

CMake supports Objective-C[++] out of the box. other build systems (e.g. autotools) as well. probably some rare used might not support it, but it has nothing to do with conan.

[memsharded]

Nice, thanks for the explanations, @SSE4, I think now it is a bit more clear, and can be moved forward.
Maybe just conditioning on the "apple" platform is enough @franramirez688, and it can be marked as ready for review

[franramirez688]

I want to add another test using Objective-C++ (typical hello.lib and demo app linking with it)

For now, I'm not adding it because of the complexity of the code. It seems that a simple Objective-C++ (Objective-C and C++) project must have a kind of wrapper in the middle of C++ and Objective-C (see more information here). I guess it's enough with those tests to verify it's working.

[memsharded]

I still feel this is problematic, having 2 mechanisms to define CXX_FLAGS (env and conf). Not related to this PR, I know it is already this way for C/C++ flags, but something we want to clarify for the future.

[franramirez688]

I absolutely agree. I can open a "look-into" feature to have this into account for future releases.