From f2f48b68a6a586f40dd8ae0e6d391b7f88756eec Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Fri, 28 Aug 2020 23:41:13 +0100
Subject: libstdc++: Fix common_type specializations for duration

My recent change to implement P0548 ("common_type and duration") was not
correct. The result of common_type_t<duration<R,P>, duration<R,P>>
should be duration<common_type_t<R>, P::type>, not duration<R, P::type>.
The common_type specialization for two different duration types was
correct, but the specializations for a single duration type (which only
exist to optimize compilation time) were wrong.

This fixes the partial specializations of common_type for a single
duration type, and also the return types of duration::operator+ and
duration::operator- which are supposed to use common_type_t<duration>.

libstdc++-v3/ChangeLog:

	* include/std/chrono (common_type): Fix partial specializations
	for a single duration type to use the common_type of the rep.
	(duration::operator+, duration::operator-): Fix return types
	to also use the common_type of the rep.
	* testsuite/20_util/duration/requirements/reduced_period.cc:
	Check duration using a rep that has common_type specialized.
---
 libstdc++-v3/include/std/chrono | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

(limited to 'libstdc++-v3/include/std')

diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
index fb25184..524d23e 100644
--- a/libstdc++-v3/include/std/chrono
+++ b/libstdc++-v3/include/std/chrono
@@ -114,13 +114,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Rep, typename _Period>
     struct common_type<chrono::duration<_Rep, _Period>,
 		       chrono::duration<_Rep, _Period>>
-    { using type = chrono::duration<_Rep, typename _Period::type>; };
+    {
+      using type = chrono::duration<typename common_type<_Rep>::type,
+				    typename _Period::type>;
+    };
 
   /// Specialization of common_type for one chrono::duration type.
   /// @relates duration
   template<typename _Rep, typename _Period>
     struct common_type<chrono::duration<_Rep, _Period>>
-    { using type = chrono::duration<_Rep, typename _Period::type>; };
+    {
+      using type = chrono::duration<typename common_type<_Rep>::type,
+				    typename _Period::type>;
+    };
 
   // 20.11.4.3 specialization of common_type (for time_point, sfinae-friendly)
 
@@ -463,13 +469,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 	// 20.11.5.3 arithmetic
 
-	constexpr duration<rep, period>
+	constexpr duration<typename common_type<rep>::type, period>
 	operator+() const
-	{ return *this; }
+	{ return duration<typename common_type<rep>::type, period>(__r); }
 
-	constexpr duration<rep, period>
+	constexpr duration<typename common_type<rep>::type, period>
 	operator-() const
-	{ return duration(-__r); }
+	{ return duration<typename common_type<rep>::type, period>(-__r); }
 
 	_GLIBCXX17_CONSTEXPR duration&
 	operator++()
-- 
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