export API

[boeschf]

• addresses Bad Any Cast Error in C++ examples #1752
• exports all symbols so arbor can be compiled as set of shared libraries

In order to export all symbols correctly, I have added one macro per library and one global macro. The content of the macros is determined at configure time depending on build variant (static/shared), compiler, and platforms (linux, mac os) and goes into the library's include directory as export.hpp when installed (at build time it resides at cmake's temporary build directory). The per-library macro is named ARB_LIBNAME_API and goes in front of to-be-exported symbols. The global macro is ARB_SYMBOL_VISIBLE. Below, I sketch out a few examples where these macros would be needed.

In this PR I tried to find all places where any annotation is required. Most of them are in the public headers (and corresponding sources) but some are also added in internal headers, which were required for the unit tests to link properly.

header.hpp

#pragma once 

#include <arbor/export.hpp>

// inline class
// no exports are needed in general (there are exceptions :) )
struct A {
    int foo() { return 42; }
    friend std::ostream& operator<<(std::ostream& o, A const & a) { o << a.foo();  return o; }
};

// template classes are inline
// no exports are needed
template<typename T>
class B {
    T m;
    B(T&& t) : m{std::move(t)} {}
};

// class declaration, implementation in source
// class needs to be exported (note this will make all member symbols visible)
class ARB_ARBOR_API C {
    void bar();
    friend std::ostream& operator<<(std::ostream& o, C const & a);
};

// inline exception class
// even though it is inline, one must make it visible! Otherwise, thrown exceptions
// will cause havoc.
class ARB_SYMBOL_VISIBLE some_error : public std::runtime_error { };

// any class which is wrapped into a std::any/arb::util::any or similar or is put into a variant
// and is part of the public interface (will be referenced outside the library) must have visibiltiy!
class ARB_SYMBOL_VISIBLE D { int a; };

// inline free function
// no need to export
void baz(int i) { std::cout << i << std::endl; }

// free function
// needs to be exported
ARB_ARBOR_API void fuu();

// (extern) global variables
// need to be exported
ARB_ARBOR_API int g;
ARB_ARBOR_API extern int h;

source.cpp

// no export at point of definition needed for member functions
// of an exported class
void C::bar() {
    throw some_error("haha");
}

// friend functions need to be exported though
ARB_ARBOR_API std::ostream& operator<<(std::ostream& o, C const& c) {
    o << 'c';
    return o;
}

// free functions need here an annotation, too!
ARB_ARBOR_API void fuu() {
    std::cout << 42 << std::endl;
}

// need to be annotated, as well
ARB_ARBOR_API int g = 10;
ARB_ARBOR_API int h = 11;

[brenthuisman]

Could you test the cibuildwheel workflow on this change? You can overwrite the ciwheel branch to trigger the action.

[update] This should not matter. Disregard.

[noraabiakar]

I have some minimal suggestions and questions. Otherwise looks good!

[boeschf]

bors try

[bors]

try

Timed out.

[boeschf]

bors try

[bors]

try

Timed out.

[noraabiakar]

bors try

[bors]

try

Build failed:

• ci/gitlab/gitlab.com