[committed] libstdc++: Check static assertions earlier in chrono::duration

[Jonathan Wakely via Gcc-patches]

Tested x86_64-linux. Pushed to trunk.

-- >8--

This ensures that we fail a static assertion before giving any other
errors. Instantiating chrono::duration<int, chrono::seconds> will now
print this before the other errors caused by it:

error: static assertion failed: period must be a specialization of ratio

libstdc++-v3/ChangeLog:

        * include/bits/chrono.h (duration): Check preconditions on
        template arguments before using them.
---
 libstdc++-v3/include/bits/chrono.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/include/bits/chrono.h 
b/libstdc++-v3/include/bits/chrono.h
index 05987ca09df..cabf61264d8 100644
--- a/libstdc++-v3/include/bits/chrono.h
+++ b/libstdc++-v3/include/bits/chrono.h
@@ -433,6 +433,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _Rep, typename _Period>
       struct duration
       {
+       static_assert(!__is_duration<_Rep>::value, "rep cannot be a duration");
+       static_assert(__is_ratio<_Period>::value,
+                     "period must be a specialization of ratio");
+       static_assert(_Period::num > 0, "period must be positive");
+
       private:
        template<typename _Rep2>
          using __is_float = treat_as_floating_point<_Rep2>;
@@ -478,11 +483,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        using rep = _Rep;
        using period = typename _Period::type;
 
-       static_assert(!__is_duration<_Rep>::value, "rep cannot be a duration");
-       static_assert(__is_ratio<_Period>::value,
-                     "period must be a specialization of ratio");
-       static_assert(_Period::num > 0, "period must be positive");
-
        // 20.11.5.1 construction / copy / destroy
        constexpr duration() = default;
 
-- 
2.38.1