Building fails with "error: lvalue required as increment operand" #4129
Description
Compiler is gcc 8.3.1
Can reproduce on godbolt with this code:
#include "fmt/format.h"
int main() {
char buffer[4];
auto result = fmt::format_to(buffer, "{}", 12345);
}
Output on godbolt:
In file included from /opt/compiler-explorer/libs/fmt/trunk/include/fmt/format.h:41,
from <source>:2:
/opt/compiler-explorer/libs/fmt/trunk/include/fmt/base.h: In instantiation of 'struct fmt::v11::detail::is_output_iterator<char [4], char, void>':
/opt/compiler-explorer/libs/fmt/trunk/include/fmt/base.h:3025:11: required by substitution of 'template<class OutputIt, class ... T, typename std::enable_if<fmt::v11::detail::is_output_iterator<typename std::remove_cv<typename std::remove_reference<_Tp>::type>::type, char>::value, int>::type <anonymous> > fmt::v11::remove_cvref_t<T> fmt::v11::format_to(OutputIt&&, fmt::v11::format_string<T ...>, T&& ...) [with OutputIt = char (&)[4]; T = {int}; typename std::enable_if<fmt::v11::detail::is_output_iterator<typename std::remove_cv<typename std::remove_reference<_Tp>::type>::type, char>::value, int>::type <anonymous> = <missing>]'
<source>:6:51: required from here
/opt/compiler-explorer/libs/fmt/trunk/include/fmt/base.h:1583:48: error: lvalue required as increment operand
It, T, void_t<decltype(*std::declval<It&>()++ = std::declval<T>())>>
~~~~~~~~~~~~~~~~~~~^~
/opt/compiler-explorer/libs/fmt/trunk/include/fmt/base.h:1583:48: error: lvalue required as increment operand
Compiler returned: 1
We discovered this issue when trying to build the fmt package after cloning the repo from github. After cloning, mkdir build && cd build && cmake .. && make
Output from this:
[ 16%] Building CXX object test/CMakeFiles/base-test.dir/base-test.cc.o
In file included from /home/nlsweet/external/fmt/test/base-test.cc:12:
/home/nlsweet/external/fmt/include/fmt/base.h: In instantiation of ‘struct fmt::v11::detail::is_output_iterator<char [4], char, void>’:
/home/nlsweet/external/fmt/include/fmt/base.h:2936:11: required by substitution of ‘template<class OutputIt, class ... T, typename std::enable_if<fmt::v11::detail::is_output_iterator<typename std::remove_cv<typename std::remove_reference<_Tp>::type>::type, char>::value, int>::type <anonymous> > fmt::v11::remove_cvref_t<T> fmt::v11::format_to(OutputIt&&, fmt::v11::format_string<T ...>, T&& ...) [with OutputIt = char (&)[4]; T = {int}; typename std::enable_if<fmt::v11::detail::is_output_iterator<typename std::remove_cv<typename std::remove_reference<_Tp>::type>::type, char>::value, int>::type <anonymous> = <missing>]’
/home/nlsweet/external/fmt/test/base-test.cc:729:51: required from here
/home/nlsweet/external/fmt/include/fmt/base.h:1576:48: error: lvalue required as increment operand
It, T, void_t<decltype(*std::declval<It&>()++ = std::declval<T>())>>
~~~~~~~~~~~~~~~~~~~^~
/home/nlsweet/external/fmt/include/fmt/base.h:1576:48: error: lvalue required as increment operand
make[2]: *** [test/CMakeFiles/base-test.dir/build.make:76: test/CMakeFiles/base-test.dir/base-test.cc.o] Error 1