compilation fails with C++14 and Intel C++ 2019 beta

[kc9jud]

If compiling with the Intel C++ 2019 beta and C++14 enabled, compilation fails:

In file included from libraries/relative/relative_me.cpp(14):
./libraries/fmt/format.h(3595): error: a literal operator template must have a template parameter list equivalent to "<char ...>"
  FMT_CONSTEXPR internal::udl_formatter<Char, CHARS...> operator""_format() {
                                                        ^

Host info:

>> lsb_release -a
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04 LTS
Release:	18.04
Codename:	bionic

Compiler info:

>> icpc --version
icpc (ICC) 19.0.0.046 20180317
Copyright (C) 1985-2018 Intel Corporation.  All rights reserved.

>> g++ --version
g++ (Ubuntu 7.3.0-16ubuntu3) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[kc9jud]

Related to #311 and #312?

[vitaut]

It looks like the Intel C++ compiler doesn't support UDL templates. Does replacing

#if FMT_USE_USER_DEFINED_LITERALS && \
    ((FMT_GCC_VERSION >= 600 && __cplusplus >= 201402L) || \
    (defined(FMT_CLANG_VERSION) && FMT_CLANG_VERSION >= 304))

with

#if FMT_USE_USER_DEFINED_LITERALS && !defined(FMT_ICC_VERSION) && \
    ((FMT_GCC_VERSION >= 600 && __cplusplus >= 201402L) || \
    (defined(FMT_CLANG_VERSION) && FMT_CLANG_VERSION >= 304))

in https://github.com/fmtlib/fmt/blob/master/include/fmt/format.h#L118 fixes the issue?

[vitaut]

Committed a tentative fix (fba352a). However, I wasn't able to verify it since I don't have an Intel compiler at hand, so feel free to reopen if the problem persists.

[kc9jud]

fba352a appears to have fixed it. Thanks!