Won't build under clang

[FlyinCow]

CMakeLists.txt:

cmake_minimum_required(VERSION 3.15)
project(proxy CXX)
set(CMAKE_CXX_STANDARD 23)

include(FetchContent)
FetchContent_Declare(
  msft_proxy4
  GIT_TAG 4.0.0 # or above
  GIT_REPOSITORY https://github.com/ngcpp/proxy.git
)

FetchContent_MakeAvailable(msft_proxy4)

add_executable(main main.cpp)
target_link_libraries(main PRIVATE msft_proxy4::proxy)

main.cpp (the example code in README.md):

#include <format>
#include <iostream>
#include <string>

#include <proxy/proxy.h>

struct Formattable : pro::facade_builder
    ::add_skill<pro::skills::format>
    ::build {};

int main() {
  static std::string str = "Hello World";
  pro::proxy<Formattable> p1 = &str;
  std::cout << std::format("*p1 = {}\n", *p1);  // Prints "*p1 = Hello World"

  pro::proxy<Formattable> p2 = std::make_unique<int>(123);
  std::cout << std::format("*p2 = {}\n", *p2);  // Prints "*p2 = 123"

  pro::proxy<Formattable> p3 = pro::make_proxy<Formattable>(3.14159);
  std::cout << std::format("*p3 = {:.2f}\n", *p3);  // Prints "*p3 = 3.14"
}

cmake config output:

[proc] 正在执行命令: /usr/sbin/cmake -DCMAKE_BUILD_TYPE:STRING=Debug -DCMAKE_EXPORT_COMPILE_COMMANDS:BOOL=TRUE -DCMAKE_C_COMPILER:FILEPATH=/usr/sbin/clang -DCMAKE_CXX_COMPILER:FILEPATH=/usr/sbin/clang++ --no-warn-unused-cli -S /home/***/workspace/proxy -B /home/***/workspace/proxy/build -G "Unix Makefiles"
[cmake] Not searching for unused variables given on the command line.
[cmake] -- The CXX compiler identification is Clang 22.1.3
[cmake] -- Detecting CXX compiler ABI info
[cmake] -- Detecting CXX compiler ABI info - done
[cmake] -- Check for working CXX compiler: /usr/sbin/clang++ - skipped
[cmake] -- Detecting CXX compile features
[cmake] -- Detecting CXX compile features - done
[cmake] -- Configuring done (0.5s)
[cmake] -- Generating done (0.0s)
[cmake] -- Build files have been written to: /home/**/workspace/proxy/build

cmake build output:

[main] 正在生成文件夹: /home/***/workspace/proxy/build main
[build] 正在启动生成
[proc] 正在执行命令: /usr/sbin/cmake --build /home/***/workspace/proxy/build --config Debug --target main -j 16 --
[build] [ 50%] Building CXX object CMakeFiles/main.dir/main.cpp.o
[build] In file included from /home/***/workspace/proxy/main.cpp:5:
[build] In file included from /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/proxy.h:7:
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:985:7: error: template 'proxy' cannot be referenced with the 'class' specifier
[build]   985 | class proxy PROD_TR_IF_ELIGIBLE
[build]       |       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:137:25: note: declared here
[build]   137 | class PRO4D_ENFORCE_EBO proxy;
[build]       |                         ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:986:5: error: expected ';' after top level declarator
[build]   986 |     : public details::facade_traits<F>::direct_accessor,
[build]       |     ^
[build]       |     ;
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:986:7: error: expected unqualified-id
[build]   986 |     : public details::facade_traits<F>::direct_accessor,
[build]       |       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1337:39: error: variable has incomplete type 'class allocated_ptr'
[build]  1337 | class PRO4D_ENFORCE_EBO allocated_ptr PROD_TR_IF_ELIGIBLE
[build]       |                                       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:44:29: note: expanded from macro 'PROD_TR_IF_ELIGIBLE'
[build]    44 | #define PROD_TR_IF_ELIGIBLE trivially_relocatable_if_eligible
[build]       |                             ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1337:25: note: forward declaration of 'pro::details::allocated_ptr'
[build]  1337 | class PRO4D_ENFORCE_EBO allocated_ptr PROD_TR_IF_ELIGIBLE
[build]       |                         ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1338:5: error: expected ';' after top level declarator
[build]  1338 |     : private alloc_aware<Alloc>,
[build]       |     ^
[build]       |     ;
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1338:7: error: expected unqualified-id
[build]  1338 |     : private alloc_aware<Alloc>,
[build]       |       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1366:19: error: redefinition of 'trivially_relocatable_if_eligible'
[build]  1366 | class compact_ptr PROD_TR_IF_ELIGIBLE
[build]       |                   ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:44:29: note: expanded from macro 'PROD_TR_IF_ELIGIBLE'
[build]    44 | #define PROD_TR_IF_ELIGIBLE trivially_relocatable_if_eligible
[build]       |                             ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1337:39: note: previous definition is here
[build]  1337 | class PRO4D_ENFORCE_EBO allocated_ptr PROD_TR_IF_ELIGIBLE
[build]       |                                       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:44:29: note: expanded from macro 'PROD_TR_IF_ELIGIBLE'
[build]    44 | #define PROD_TR_IF_ELIGIBLE trivially_relocatable_if_eligible
[build]       |                             ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1367:5: error: expected ';' after top level declarator
[build]  1367 |     : public indirect_ptr<compact_ptr_storage<T, Alloc>> {
[build]       |     ^
[build]       |     ;
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1367:7: error: expected unqualified-id
[build]  1367 |     : public indirect_ptr<compact_ptr_storage<T, Alloc>> {
[build]       |       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1399:26: error: redefinition of 'trivially_relocatable_if_eligible'
[build]  1399 | class shared_compact_ptr PROD_TR_IF_ELIGIBLE
[build]       |                          ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:44:29: note: expanded from macro 'PROD_TR_IF_ELIGIBLE'
[build]    44 | #define PROD_TR_IF_ELIGIBLE trivially_relocatable_if_eligible
[build]       |                             ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1337:39: note: previous definition is here
[build]  1337 | class PRO4D_ENFORCE_EBO allocated_ptr PROD_TR_IF_ELIGIBLE
[build]       |                                       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:44:29: note: expanded from macro 'PROD_TR_IF_ELIGIBLE'
[build]    44 | #define PROD_TR_IF_ELIGIBLE trivially_relocatable_if_eligible
[build]       |                             ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1400:5: error: expected ';' after top level declarator
[build]  1400 |     : public indirect_ptr<shared_compact_ptr_storage<T, Alloc>> {
[build]       |     ^
[build]       |     ;
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1400:7: error: expected unqualified-id
[build]  1400 |     : public indirect_ptr<shared_compact_ptr_storage<T, Alloc>> {
[build]       |       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1438:26: error: redefinition of 'trivially_relocatable_if_eligible'
[build]  1438 | class strong_compact_ptr PROD_TR_IF_ELIGIBLE
[build]       |                          ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:44:29: note: expanded from macro 'PROD_TR_IF_ELIGIBLE'
[build]    44 | #define PROD_TR_IF_ELIGIBLE trivially_relocatable_if_eligible
[build]       |                             ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1337:39: note: previous definition is here
[build]  1337 | class PRO4D_ENFORCE_EBO allocated_ptr PROD_TR_IF_ELIGIBLE
[build]       |                                       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:44:29: note: expanded from macro 'PROD_TR_IF_ELIGIBLE'
[build]    44 | #define PROD_TR_IF_ELIGIBLE trivially_relocatable_if_eligible
[build]       |                             ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1439:5: error: expected ';' after top level declarator
[build]  1439 |     : public indirect_ptr<strong_weak_compact_ptr_storage<T, Alloc>> {
[build]       |     ^
[build]       |     ;
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1439:7: error: expected unqualified-id
[build]  1439 |     : public indirect_ptr<strong_weak_compact_ptr_storage<T, Alloc>> {
[build]       |       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1483:7: error: template 'weak_compact_ptr' cannot be referenced with the 'class' specifier
[build]  1483 | class weak_compact_ptr PROD_TR_IF_ELIGIBLE {
[build]       |       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1436:7: note: declared here
[build]  1436 | class weak_compact_ptr;
[build]       |       ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1484:1: error: expected expression
[build]  1484 | public:
[build]       | ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1534:40: error: expected '>'
[build]  1534 |   if constexpr (proxiable<allocated_ptr<T, Alloc>, F>) {
[build]       |                                        ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1534:26: note: to match this '<'
[build]  1534 |   if constexpr (proxiable<allocated_ptr<T, Alloc>, F>) {
[build]       |                          ^
[build] /home/***/workspace/proxy/build/_deps/msft_proxy4-src/include/proxy/v4/proxy.h:1534:40: error: type name requires a specifier or qualifier
[build]  1534 |   if constexpr (proxiable<allocated_ptr<T, Alloc>, F>) {
[build]       |                                        ^
[build] fatal error: too many errors emitted, stopping now [-ferror-limit=]
[build] 20 errors generated.
[build] make[3]: *** [CMakeFiles/main.dir/build.make:79: CMakeFiles/main.dir/main.cpp.o] Error 1
[build] make[2]: *** [CMakeFiles/Makefile2:109: CMakeFiles/main.dir/all] Error 2
[build] make[1]: *** [CMakeFiles/Makefile2:116: CMakeFiles/main.dir/rule] Error 2
[build] make: *** [Makefile:169: main] Error 2
[proc] 命令“/usr/sbin/cmake --build /home/***/workspace/proxy/build --config Debug --target main -j 16 --”已退出，代码为 2
[driver] 生成完毕: 00:00:00.740
[build] 生成已完成，退出代码为 2

clang --version:

clang version 22.1.3
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

[mingxwa]

Hi @FlyinCow,

Thanks for reporting this. It should be fixed in the latest release 4.0.2.

The root cause is a bit unusual. Trivial relocation was originally voted into C++26, so Proxy implemented support for it. Before C++26 was finalized, however, the feature was removed from the standard.

Proxy was checking the feature-test macro __cpp_trivial_relocatability and only enabling the related code when that macro was present, which was the intended behavior. The problem arose because Clang 22 removed the feature implementation but appears to have left the feature-test macro defined, which led to this mismatch.

Version 4.0.2 no longer has this problem because I removed the related code after the feature's removal from C++26 was confirmed. Sorry for the trouble.

Mingxin