Clang-8.0 (C++ 17 standard) compile StrFormat failed

[fcharlie]

When I build some program which depend with absl str_format use Clang-8.0 (C++ 17 standard ). The compiler report:

'FormatSpecTemplate' is unavailable: Format std::string is not
constexpr.

OS:

# lsb_release
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.2 LTS
Release:	18.04
Codename:	bionic

Linux Kernel:

#uname -a
Linux somehost 4.18.0-15-generic #16~18.04.1-Ubuntu SMP Thu Feb 7 14:06:04 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Clang Is 8.0 RC3, Version Details:

#clang -v
clang version 8.0.0 (clangbuilder 355381)
Target: x86_64-clangbuilder-linux-gnu
Thread model: posix
InstalledDir: /opt/llvm-8.0/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.4.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Candidate multilib: .;@m64
Selected multilib: .;@m64

Code:

#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"
#include <iostream>
#include <string>

int main(int argc, const char **argv) {
  for (int i = 0; i < argc; ++i) {
    std::string s = argv[i];
    std::cout << "--- >" << absl::StrFormat("Arg %d is %s\n", i, s);
    std::cout << absl::StrCat("Arg ", i, ": ", argv[i], "\n");
  }
}

cmake

# Required as the first line
cmake_minimum_required(VERSION 3.12)

# Define the crrent project
project(main VERSION 0.1)

# Tell Abseil which C++ standard to use
set(CMAKE_CXX_STANDARD 17)

# Process abseil with CMake
add_subdirectory(abseil-cpp)

# Define the target executable and its dependency on Abseil
add_executable(main main.cc)
target_link_libraries(main
  absl::str_format
  absl::strings
)

Output:

/tmp/abseil-hello/cmake-hello/main.cc:9:45: error: 'FormatSpecTemplate' is unavailable: Format std::string is not
      constexpr.
    std::cout << "--- >" << absl::StrFormat("Arg %d is %s\n", i, s);
                                            ^
/tmp/abseil-hello/cmake-hello/abseil-cpp/absl/strings/internal/str_format/bind.h:82:3: note: 'FormatSpecTemplate' has
      been explicitly marked unavailable here
  FormatSpecTemplate(...)  // NOLINT
  ^
1 error generated.
CMakeFiles/main.dir/build.make:62: recipe for target 'CMakeFiles/main.dir/main.cc.o' failed
make[2]: *** [CMakeFiles/main.dir/main.cc.o] Error 1
CMakeFiles/Makefile2:79: recipe for target 'CMakeFiles/main.dir/all' failed
make[1]: *** [CMakeFiles/main.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

[EricWF]

Thanks for the report. This appears to be a regression in the upcoming Clang release. We may have caught it in time to fix.

Here's a reproducer on godbolt: https://godbolt.org/z/k5RlV9

I'll do more investigation in the morning.

[fcharlie]

Thanks for the report. This appears to be a regression in the upcoming Clang release. We may have caught it in time to fix.

Here's a reproducer on godbolt: https://godbolt.org/z/k5RlV9

I'll do more investigation in the morning.

Then this problem should be independent of Absl, GCC-8.0 Clang-7.0 C++17/C++14 did not find this error.

[EricWF]

Here's the fully reduced bug: https://godbolt.org/z/ksAjmq
Here's the Clang fix: https://reviews.llvm.org/D59038

I'll close this once I know if the fix will make it into Clang 8.

[fcharlie]

@EricWF Thanks.

[fcharlie]

Rebuild clang and use it. This issue has been fixed. Thanks @EricWF

clang version 8.0.0 (clangbuilder 356006)
Target: x86_64-clangbuilder-linux-gnu
Thread model: posix
InstalledDir: /opt/llvm-8.0/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.4.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Candidate multilib: .;@m64
Selected multilib: .;@m64

[EricWF]

Thanks for confirming the fix.

I can confirm the fix will be a part of Clang 8.0 :-)