remove Boost.DLL dependency by doing DLL handling ourselves

include/cpp2util.h

@@ -283,6 +283,15 @@
 #endif
 
 
+#if defined(_WIN32)
+#define CPPFRONTAPI __declspec(dllexport)
+#else
+#define CPPFRONTAPI  __attribute__ ((visibility ("default")))
+#endif
+
+#define CPP2_C_API extern "C" CPPFRONTAPI
+
+
 namespace cpp2 {
 
 

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 +1,153 @@
+#include <cstdlib>
+#include <functional>
+#include <string>
+#include <string_view>
+#include <utility>
+#include "cpp2util.h"
+
+#ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+#include <Windows.h>
+#else
+#include <dlfcn.h>
+#endif // _WIN32
+
+namespace cpp2::meta {
+
+class dll
+{
+public:
+    dll(std::string const& path)
+    {
+#ifdef _WIN32
+        handle_ = static_cast<void*>(LoadLibraryA(path.c_str()));
+#else
+        handle_ = static_cast<void*>(dlopen(path.c_str(), RTLD_NOW|RTLD_LOCAL));
+#endif // _WIN32
+        // TODO(Herb/Johel): Decide a user-friendlier way of reporting this.
+        if(handle_ == nullptr)
+            std::cerr << "Error while loading DLL '" << path << "': " << get_last_error_() << '\n';
+    }
+
+    ~dll() noexcept
+    {
+        if(handle_ != nullptr)
+        {
+#ifdef _WIN32
+            FreeLibrary(static_cast<HMODULE>(handle_));
+#else
+            dlclose(handle_);
+#endif // _WIN32
+        }
+    }
+
+    // Uncopyable
+    dll(dll&) = delete;
+    dll(dll const&) = delete;
+    auto operator=(dll const&) -> dll& = delete;
+    // Unmovable
+    dll(dll&& from) = delete;
+    auto operator=(dll&& from) -> dll& = delete;
+
+    auto is_open() noexcept -> bool { return handle_ != nullptr; }
+
+    template<typename T>
+    auto get_alias(std::string const& name) noexcept -> T*
+    {
+#ifdef _WIN32
+        auto symbol = GetProcAddress(static_cast<HMODULE>(handle_), name.c_str());
+#else
+        auto symbol = dlsym(handle_, name.c_str());
+        if(symbol == nullptr)
+        {
+            // Some platforms export with additional underscore, so try that.
+            auto const us_name = "_" + name;
+            symbol = dlsym(handle_, us_name.c_str());
+        }
+#endif // _WIN32
+        // TODO(Herb/Johel): Decide a user-friendlier way of reporting this.
+        if(symbol == nullptr)
+            std::cerr << "Error while looking up DLL symbol '" << name << "': " << get_last_error_() << '\n';
+        return function_cast_<T*>(symbol);
+    }
+private:
+    void* handle_{nullptr};
+
+    template<typename T>
+    static auto function_cast_(auto ptr) noexcept -> T {
+        using generic_function_ptr = void (*)(void);
+        return reinterpret_cast<T>(reinterpret_cast<generic_function_ptr>(ptr));
+    }
+
+    static auto get_last_error_() noexcept -> std::string {
+#ifdef _WIN32
+        DWORD errorMessageID = GetLastError();
+        if(errorMessageID == 0)
+            return {}; // No error message has been recorded
+        LPSTR messageBuffer = nullptr;
+        auto size = FormatMessageA(
+            FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS,
+            nullptr,
+            errorMessageID,
+            MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
+            &messageBuffer,
+            0,
+            nullptr
+        );
+        std::string message(messageBuffer, static_cast<size_t>(size));
+        LocalFree(messageBuffer);
+        return message;
+#else
+        return std::string{dlerror()};
+#endif // _WIN32
+    }
+
+};
+
+
+//  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&)>
+{
+    // FIXME: On Windows, using this approach with the system apis not set to utf8, will
+    // break if a metafunction library contains unicode codepoints in its name, a proper
+    // way to handle this would be to use _wgetenv and use wchar_t strings for the dll opening
+    // function
+    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>(std::string(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_"
+                        "\nCPP2_C_API void cpp2_metafunction_"
                         + identifier
-                        + " = &"
+                        + "(void* t) { "
                         + identifier
-                        + ";"
+                        + "(*static_cast<cpp2::meta::type_declaration*>(t));"
+                        + " }"
                     );
                 }
             }