[gcc/devel/c++-modules] libstdc++: Fix noexcept-specifier for istream_iterator

[Nathan Sidwell]

https://gcc.gnu.org/g:8566286eaeb9a977339df88212826150767f1203

commit 8566286eaeb9a977339df88212826150767f1203
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Feb 24 14:22:21 2020 +0000

    libstdc++: Fix noexcept-specifier for istream_iterator
    
    Somehow I missed that the _M_value member can throw on construction.
    
    	* include/bits/stream_iterator.h (istream_iterator(default_sentinel_t)):
    	Make noexcept-specifier conditional.
    	* testsuite/24_iterators/istream_iterator/cons/sentinel.cc: Check
    	noexcept-specifier.

Diff:
---
 libstdc++-v3/ChangeLog                                           | 5 +++++
 libstdc++-v3/include/bits/stream_iterator.h                      | 3 ++-
 .../testsuite/24_iterators/istream_iterator/cons/sentinel.cc     | 9 +++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index e18f9d0..eefb2a5 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,6 +1,11 @@
 2020-02-24  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/bits/stream_iterator.h (istream_iterator(default_sentinel_t)):
+	Make noexcept-specifier conditional.
+	* testsuite/24_iterators/istream_iterator/cons/sentinel.cc: Check
+	noexcept-specifier.
+
+	* include/bits/stream_iterator.h (istream_iterator(default_sentinel_t)):
 	Add constructor.
 	(operator==(istream_iterator, default_sentinel_t)): Add operator.
 	(ostream_iterator::difference_type): Define to ptrdiff_t for C++20.
diff --git a/libstdc++-v3/include/bits/stream_iterator.h b/libstdc++-v3/include/bits/stream_iterator.h
index 1ddf647..9d8ead0 100644
--- a/libstdc++-v3/include/bits/stream_iterator.h
+++ b/libstdc++-v3/include/bits/stream_iterator.h
@@ -79,7 +79,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cplusplus > 201703L
       constexpr
-      istream_iterator(default_sentinel_t) noexcept
+      istream_iterator(default_sentinel_t)
+      noexcept(is_nothrow_default_constructible_v<_Tp>)
       : istream_iterator() { }
 #endif
 
diff --git a/libstdc++-v3/testsuite/24_iterators/istream_iterator/cons/sentinel.cc b/libstdc++-v3/testsuite/24_iterators/istream_iterator/cons/sentinel.cc
index 77a1949..b890f04 100644
--- a/libstdc++-v3/testsuite/24_iterators/istream_iterator/cons/sentinel.cc
+++ b/libstdc++-v3/testsuite/24_iterators/istream_iterator/cons/sentinel.cc
@@ -19,9 +19,18 @@
 // <http://www.gnu.org/licenses/>.
 
 #include <iterator>
+#include <istream>
 
 // C++20 doesn't require this to be non-throwing.
 static_assert( std::is_nothrow_constructible_v<std::istream_iterator<int>,
 					       std::default_sentinel_t> );
 
 constexpr std::istream_iterator<int> i = std::default_sentinel;
+
+struct X { X() noexcept(false); };
+std::istream& operator<<(std::istream&, X&);
+
+static_assert( std::is_constructible_v<std::istream_iterator<X>,
+				       std::default_sentinel_t> );
+static_assert( ! std::is_nothrow_constructible_v<std::istream_iterator<X>,
+						 std::default_sentinel_t> );