GCC 5.3 error: could not convert '(const char*)"-"' from 'const char*' to 'au::detail::StringConstant<1ul>'

[to-s]

Tried to update some old sources from 0.3.5 to the current release, but seems broken since https://github.com/aurora-opensource/au/releases/tag/0.4.0. Any ideas how to handle that?

In file included from <source>:2:0:
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: In static member function 'static constexpr au::detail::StringConstant<1ul> au::detail::SignIfPositiveIs<false>::value()':
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:560:57: error: could not convert '(const char*)"-"' from 'const char*' to 'au::detail::StringConstant<1ul>'
     static constexpr StringConstant<1> value() { return "-"; }
                                                         ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: In function 'constexpr uintmax_t au::detail::find_prime_factor(uintmax_t)':
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2854:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (p * p > n) {
                   ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: At global scope:
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:5600:90: error: 'constexpr' is not allowed in declaration of friend template specialization 'au::AlwaysDivisibleQuantity<U, R> unblock_int_div<U, R>(au::Quantity<U, R>)'
     friend constexpr AlwaysDivisibleQuantity<U, R> unblock_int_div<U, R>(Quantity<U, R> q);
                                                                                          ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:5601:87: error: 'constexpr' is not allowed in declaration of friend template specialization 'au::AlwaysDivisibleQuantity<au::UnitProduct<>, R> unblock_int_div<R>(R)'
     friend constexpr AlwaysDivisibleQuantity<UnitProductT<>, R> unblock_int_div<R>(R x);
                                                                                       ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: In instantiation of 'struct au::Prime<11ul>':
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2981:65:   required from 'struct au::detail::OrderByValue<au::Prime<7ul>, au::Prime<11ul> >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2355:8:   required from 'struct au::LexicographicTotalOrdering<au::Prime<7ul>, au::Prime<11ul>, au::detail::OrderByValue>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2985:8:   required from 'struct au::InOrderFor<au::Magnitude, au::Prime<7ul>, au::Prime<11ul> >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2512:8:   required from 'struct au::PackProduct<au::Magnitude, au::Magnitude<au::Pow<au::Prime<7ul>, 1l> >, au::Magnitude<au::Prime<11ul> > >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2179:90:   required by substitution of 'template<template<class ...> class Pack, class ... Ts> using PackProductT = au::detail::SimplifyBasePowersT<typename au::PackProduct<Pack, Ts>::type> [with Pack = au::Magnitude; Ts = {au::Magnitude<au::Pow<au::Prime<7ul>, 1l> >, au::Magnitude<au::Prime<11ul> >}]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3133:97:   recursively required from 'struct au::detail::PrimeFactorization<77ul>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3133:97:   required from 'struct au::detail::PrimeFactorization<231ul>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3119:65:   required by substitution of 'template<long unsigned int N> using PrimeFactorizationT = typename au::detail::PrimeFactorization::type [with long unsigned int N = 231ul]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3140:43:   required from 'constexpr auto au::mag() [with long unsigned int N = 231ul]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:7258:56:   required from here
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2960:5: error: static assertion failed: Prime<N> requires that N is prime
     static_assert(detail::is_prime(N), "Prime<N> requires that N is prime");
     ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: In instantiation of 'struct au::Prime<463ul>':
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2981:65:   required from 'struct au::detail::OrderByValue<au::Prime<2ul>, au::Prime<463ul> >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2355:8:   required from 'struct au::LexicographicTotalOrdering<au::Prime<2ul>, au::Prime<463ul>, au::detail::OrderByValue>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2985:8:   required from 'struct au::InOrderFor<au::Magnitude, au::Prime<2ul>, au::Prime<463ul> >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2512:8:   required from 'struct au::PackProduct<au::Magnitude, au::Magnitude<au::Pow<au::Prime<2ul>, 2l> >, au::Magnitude<au::Prime<463ul> > >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2179:90:   required by substitution of 'template<template<class ...> class Pack, class ... Ts> using PackProductT = au::detail::SimplifyBasePowersT<typename au::PackProduct<Pack, Ts>::type> [with Pack = au::Magnitude; Ts = {au::Magnitude<au::Pow<au::Prime<2ul>, 2l> >, au::Magnitude<au::Prime<463ul> >}]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2937:52:   required by substitution of 'template<class ... BPs> using MagProductT = au::PackProductT<au::Magnitude, BPs ...> [with BPs = {au::Magnitude<au::Pow<au::Prime<2ul>, 2l> >, au::detail::PrimeFactorization<463ul>::type}]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3133:97:   required from 'struct au::detail::PrimeFactorization<1852ul>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3119:65:   required by substitution of 'template<long unsigned int N> using PrimeFactorizationT = typename au::detail::PrimeFactorization::type [with long unsigned int N = 1852ul]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3140:43:   required from 'constexpr auto au::mag() [with long unsigned int N = 1852ul]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:7384:55:   required from here
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2960:5: error: static assertion failed: Prime<N> requires that N is prime
g++: internal compiler error: Killed (program cc1plus)
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
ASM generation compiler returned: 4
In file included from <source>:2:0:
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: In static member function 'static constexpr au::detail::StringConstant<1ul> au::detail::SignIfPositiveIs<false>::value()':
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:560:57: error: could not convert '(const char*)"-"' from 'const char*' to 'au::detail::StringConstant<1ul>'
     static constexpr StringConstant<1> value() { return "-"; }
                                                         ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: In function 'constexpr uintmax_t au::detail::find_prime_factor(uintmax_t)':
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2854:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (p * p > n) {
                   ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: At global scope:
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:5600:90: error: 'constexpr' is not allowed in declaration of friend template specialization 'au::AlwaysDivisibleQuantity<U, R> unblock_int_div<U, R>(au::Quantity<U, R>)'
     friend constexpr AlwaysDivisibleQuantity<U, R> unblock_int_div<U, R>(Quantity<U, R> q);
                                                                                          ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:5601:87: error: 'constexpr' is not allowed in declaration of friend template specialization 'au::AlwaysDivisibleQuantity<au::UnitProduct<>, R> unblock_int_div<R>(R)'
     friend constexpr AlwaysDivisibleQuantity<UnitProductT<>, R> unblock_int_div<R>(R x);
                                                                                       ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: In instantiation of 'struct au::Prime<11ul>':
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2981:65:   required from 'struct au::detail::OrderByValue<au::Prime<7ul>, au::Prime<11ul> >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2355:8:   required from 'struct au::LexicographicTotalOrdering<au::Prime<7ul>, au::Prime<11ul>, au::detail::OrderByValue>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2985:8:   required from 'struct au::InOrderFor<au::Magnitude, au::Prime<7ul>, au::Prime<11ul> >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2512:8:   required from 'struct au::PackProduct<au::Magnitude, au::Magnitude<au::Pow<au::Prime<7ul>, 1l> >, au::Magnitude<au::Prime<11ul> > >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2179:90:   required by substitution of 'template<template<class ...> class Pack, class ... Ts> using PackProductT = au::detail::SimplifyBasePowersT<typename au::PackProduct<Pack, Ts>::type> [with Pack = au::Magnitude; Ts = {au::Magnitude<au::Pow<au::Prime<7ul>, 1l> >, au::Magnitude<au::Prime<11ul> >}]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3133:97:   recursively required from 'struct au::detail::PrimeFactorization<77ul>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3133:97:   required from 'struct au::detail::PrimeFactorization<231ul>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3119:65:   required by substitution of 'template<long unsigned int N> using PrimeFactorizationT = typename au::detail::PrimeFactorization::type [with long unsigned int N = 231ul]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3140:43:   required from 'constexpr auto au::mag() [with long unsigned int N = 231ul]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:7258:56:   required from here
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2960:5: error: static assertion failed: Prime<N> requires that N is prime
     static_assert(detail::is_prime(N), "Prime<N> requires that N is prime");
     ^
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh: In instantiation of 'struct au::Prime<463ul>':
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2981:65:   required from 'struct au::detail::OrderByValue<au::Prime<2ul>, au::Prime<463ul> >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2355:8:   required from 'struct au::LexicographicTotalOrdering<au::Prime<2ul>, au::Prime<463ul>, au::detail::OrderByValue>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2985:8:   required from 'struct au::InOrderFor<au::Magnitude, au::Prime<2ul>, au::Prime<463ul> >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2512:8:   required from 'struct au::PackProduct<au::Magnitude, au::Magnitude<au::Pow<au::Prime<2ul>, 2l> >, au::Magnitude<au::Prime<463ul> > >'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2179:90:   required by substitution of 'template<template<class ...> class Pack, class ... Ts> using PackProductT = au::detail::SimplifyBasePowersT<typename au::PackProduct<Pack, Ts>::type> [with Pack = au::Magnitude; Ts = {au::Magnitude<au::Pow<au::Prime<2ul>, 2l> >, au::Magnitude<au::Prime<463ul> >}]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2937:52:   required by substitution of 'template<class ... BPs> using MagProductT = au::PackProductT<au::Magnitude, BPs ...> [with BPs = {au::Magnitude<au::Pow<au::Prime<2ul>, 2l> >, au::detail::PrimeFactorization<463ul>::type}]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3133:97:   required from 'struct au::detail::PrimeFactorization<1852ul>'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3119:65:   required by substitution of 'template<long unsigned int N> using PrimeFactorizationT = typename au::detail::PrimeFactorization::type [with long unsigned int N = 1852ul]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:3140:43:   required from 'constexpr auto au::mag() [with long unsigned int N = 1852ul]'
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:7384:55:   required from here
/app/aurora-opensource.github.io/au/0.4.0/au_all_units.hh:2960:5: error: static assertion failed: Prime<N> requires that N is prime
g++: internal compiler error: Killed (program cc1plus)
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
Execution build compiler returned: 4
Build failed

Examples on Goldbolt

Broken one using 0.4.0: https://godbolt.org/z/e3PcfefEx

Last working 0.3.5: https://godbolt.org/z/dd6cbn6a5

[chiphogg]

Thanks for this helpfully detailed report!

The short answer is that this compiler version is in the "best effort" category, and is just too old (2016) for us to support robustly. I think these errors are all problems with gcc 5.3 specifically. In fact, at least one of them is due to a known bug which was fixed in gcc 5.4 (!).

That said: this doesn't mean we're waving the white flag here. 🙂 0.3.5 was working for you, and I hope we can get future versions working for you too.

https://godbolt.org/z/h1hshPYWh is a good debugging setup: it's a godbolt project with an au.hh file, where you can drop in any single-file version of the library. If you're tinkering with the library locally, then you can use the make-single-file tool to regenerate the single file, and paste it there. The current contents are equivalent to today's main, but with two small changes that I am currently planning to put up for review and land. You can see that we've fixed two of the three errors. I think the first step is to get to where we've fixed all three errors, so we can see what the full code changes would look like.

Unfortunately, the third one is weird and hard to debug. It is telling me that 113 is not prime. I'm still digging into why this is, but already I've found that the primality checker gives a different response (!) when run in constexpr than when run at runtime (again, on gcc 5.3). The "D" parameter in the strong Lucas test appears to be giving -11 instead of 5. I'll do my best to get to the bottom of this. https://godbolt.org/z/7WGE4j3xG is a checkpoint for my debugging for me to come back to later.

Assuming that we can fix all 3 errors with an innocuous change, we could consider producing a hotfix release artifact for 0.4.1 and 0.5.0. We don't really have well defined procedures for doing that, but we may be able to figure something out. This should unblock you in resuming the upgrade journey to the latest version. And by the way: I'm glad to see you're making the effort to keep the library up to date! The newer versions have some exciting and satisfying changes, and I hope you'll find them useful.

[chiphogg]

https://godbolt.org/z/6TbTn1PWb appears to work.

I have learned that gcc 5.3 has really terrible and unreliable constexpr support. Nevertheless, I'll put up a fix that I hope would work for you!

[chiphogg]

Check out #549 if you want to see what the "fixes" were. 😅

[chiphogg]

@to-s, it looks like the latest main now works: https://godbolt.org/z/EoEaK3aWs. What else do you need to unblock you from upgrading the library?

One route would be the DIY route, where you cherry pick b5026ff (#549) onto each release, and regenerate your single file from those contents.

Another route might be for us to figure out procedures for how to create a new release artifact, and then attach an artifact to 0.4.1 and 0.5.0. That might take a little while, because we'd need to invent new procedures.

Maybe a middle route could be to post some ad hoc release artifacts as attachments to this issue. I'd need to know how you're installing the library in your project so I can produce the most convenient kind of artifact.

Let me know how you want to proceed!

[chiphogg]

As for what it will take to close this issue: at the very least, we should add a godbolt link to a new list of "problem" compiler versions, and check these versions when we're close to cutting a new release. If we do that, then it should keep gcc 5.3 from breaking in any future releases, even though it's still in the "best effort" tier.