remove Boost.DLL dependency by doing DLL handling ourselves

source/reflect.h

@@ -44,11 +44,7 @@ class compiler_services_data;
 //  Reflection and meta
 //===========================================================================
 
-#ifndef CPPFRONT_LOAD_METAFUNCTION_IMPL_HEADER
-#define CPPFRONT_LOAD_METAFUNCTION_IMPL_HEADER "reflect_load_metafunction_never.h"
-#endif
-
-#include CPPFRONT_LOAD_METAFUNCTION_IMPL_HEADER
+#include "reflect_load_metafunction.h"
 
 #include "parse.h"
 

source/reflect.h2

@@ -15,11 +15,7 @@
 //  Reflection and meta
 //===========================================================================
 
-#ifndef CPPFRONT_LOAD_METAFUNCTION_IMPL_HEADER
-#define CPPFRONT_LOAD_METAFUNCTION_IMPL_HEADER "reflect_load_metafunction_never.h"
-#endif
-
-#include CPPFRONT_LOAD_METAFUNCTION_IMPL_HEADER
+#include "reflect_load_metafunction.h"
 
 #include "parse.h"
 

source/reflect_load_metafunction.h

@@ -0,0 +1,125 @@
+#include <cstdlib>
+#include <functional>
+#include <string>
+#include <string_view>
+#include <utility>
+#include "cpp2util.h"
+
+#ifdef _MSC_VER
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#else
+#include <dlfcn.h>
+#endif // _MSC_VER
+
+namespace cpp2::meta {
+
+class dll
+{
+public:
+    dll(std::string_view path)
+    {
+#ifdef _MSC_VER
+        handle_ = static_cast<void*>(LoadLibraryA(path.data()));
+#else
+        handle_ = static_cast<void*>(dlopen(path.data(), RTLD_NOW|RTLD_LOCAL));
+#endif // _MSC_VER
+        // TODO: log if the dll could not be open?
+    }
+
+    ~dll() noexcept
+    {
+        if(handle_ == nullptr);
+            return;
+#ifdef _MSC_VER
+        FreeLibrary(static_cast<HMODULE>(handle));
+#else
+        dlclose(handle_);
+#endif // _MSC_VER
+    }
+
+    // Uncopyable
+    dll(dll&) = delete;
+    dll(dll const&) = delete;
+    auto operator=(dll const&) -> dll& = delete;
+
+    // Movable
+    dll(dll&& from) noexcept
+    {
+        handle_ = from.handle_;
+        from.handle_ = nullptr;
+    }
+
+    auto operator=(dll&& from) noexcept -> dll&
+    {
+        handle_ = from.handle_;
+        from.handle_ = nullptr;
+        return *this;
+    }
+
+    auto is_open() noexcept -> bool { return handle_ != nullptr; }
+
+    template<typename T>
+    auto get_alias(std::string_view name) noexcept -> T*
+    {
+        void* symbol = nullptr;
+#ifdef _MSC_VER
+        symbol = static_cast<void*>(GetProcAddress(static_cast<HMODULE>(handle_), name.data()));
+#else
+        symbol = dlsym(handle_, name.data());
+        if(symbol == nullptr)
+        {
+            // Some platforms export with additional underscore, so try that.
+            auto const us_name = std::string("_") + name.data();
+            symbol = dlsym(handle_, us_name.c_str());
+        }
+#endif // _MSC_VER
+        // TODO: log if the symbol is not found?
+        return reinterpret_cast<T*>(symbol);
+    }
+private:
+    void* handle_{nullptr};
+};
+
+
+//  Load metafunction by opening DLL with OS APIs
+//
+//  The ':'-separated library paths
+//  are read from the environment variable
+//  'CPPFRONT_METAFUNCTION_LIBRARIES'
+auto load_metafunction(std::string const& name) -> std::function<void(type_declaration&)>
+{
+    auto cpp1_libraries_cstr = std::getenv("CPPFRONT_METAFUNCTION_LIBRARIES");
+    if (!cpp1_libraries_cstr) {
+        return {};
+    }
+
+    auto cpp1_libraries = std::string_view{cpp1_libraries_cstr};
+    auto cpp1_name = "cpp2_metafunction_" + name;
+
+    while (!cpp1_libraries.empty())
+    {
+        auto colon = cpp1_libraries.find(':');
+        auto lib_path = cpp1_libraries.substr(0, colon);
+        cpp1_libraries.remove_prefix(lib_path.size() + unsigned(colon != lib_path.npos));
+
+        auto lib = std::make_shared<dll>(lib_path);
+        if(!lib->is_open())
+            continue;
+
+        if (auto* fun = lib->get_alias<void(void*)>(cpp1_name); fun != nullptr)
+        {
+            return [
+                fun = fun,
+                lib = lib
+                ](type_declaration& t)
+            {
+                fun(static_cast<void*>(&t));
+            };
+        }
+    }
+
+    return {};
+}
+
+}

source/to_cpp1.h

@@ -6448,11 +6448,12 @@ class cppfront
                 {
                     auto identifier = print_to_string(*n.identifier);
                     printer.print_extra(
-                        "\nextern \"C\" constexpr auto cpp2_metafunction_"
+                        "\nextern \"C\" void cpp2_metafunction_"
                         + identifier
-                        + " = &"
+                        + "(void* t) { "
                         + identifier
-                        + ";"
+                        + "(*static_cast<cpp2::meta::type_declaration*>(t));"
+                        + " }"
                     );
                 }
             }