PR libstdc++/58265 add noexcept to basic_string::assign(basic_string&&)

	PR libstdc++/58265
	* include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI]
	(basic_string::assign(basic_string&&)): Add conditional noexcept
	depending on the allocator's is_always_equal property (LWG 2063).
	* testsuite/21_strings/basic_string/modifiers/assign/char/
	move_assign.cc: Check for non-throwing exception specification.
	* testsuite/21_strings/basic_string/modifiers/assign/wchar_t/
	move_assign.cc: Likewise.

From-SVN: r262447

libstdc++-v3/ChangeLog

@@ -2,6 +2,15 @@
 
 	PR libstdc++/58265
 	* include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI]
+	(basic_string::assign(basic_string&&)): Add conditional noexcept
+	depending on the allocator's is_always_equal property (LWG 2063).
+	* testsuite/21_strings/basic_string/modifiers/assign/char/
+	move_assign.cc: Check for non-throwing exception specification.
+	* testsuite/21_strings/basic_string/modifiers/assign/wchar_t/
+	move_assign.cc: Likewise.
+
+	PR libstdc++/58265
+	* include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI]
 	[_GLIBCXX_FULLY_DYNAMIC_STRING==0] (basic_string::basic_string()):
 	Add GLIBCXX_NOEXCEPT.
 	(basic_string::operator=(basic_string&&)): Add _GLIBCXX_NOEXCEPT_IF

libstdc++-v3/include/bits/basic_string.h

@@ -725,7 +725,6 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  The contents of @a str are moved into this string (without copying).
        *  @a str is a valid, but unspecified string.
        **/
-      // PR 58265, this should be noexcept.
       // _GLIBCXX_RESOLVE_LIB_DEFECTS
       // 2063. Contradictory requirements for string move assignment
       basic_string&
@@ -4275,9 +4274,9 @@ _GLIBCXX_END_NAMESPACE_CXX11
        *  This function sets this string to the exact contents of @a __str.
        *  @a __str is a valid, but unspecified string.
        */
-      // PR 58265, this should be noexcept.
       basic_string&
       assign(basic_string&& __str)
+      noexcept(allocator_traits<_Alloc>::is_always_equal::value)
       {
 	this->swap(__str);
 	return *this;

libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/char/move_assign.cc

@@ -32,6 +32,9 @@ void test01()
   a.push_back('1');
   b.assign(std::move(a));
   VERIFY( b.size() == 1 && b[0] == '1' && a.size() == 0 );
+
+  // True for std::allocator because is_always_equal, but not true in general:
+  static_assert(noexcept(a.assign(std::move(b))), "lwg 2063");
 }
 
 int main()

libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/wchar_t/move_assign.cc

@@ -32,6 +32,9 @@ void test01()
   a.push_back(L'1');
   b.assign(std::move(a));
   VERIFY( b.size() == 1 && b[0] == '1' && a.size() == 0 );
+
+  // True for std::allocator because is_always_equal, but not true in general:
+  static_assert(noexcept(a.assign(std::move(b))), "lwg 2063");
 }
 
 int main()