Update comments for February 2021 LWG issues (#1686)

stl/inc/iterator

@@ -1084,7 +1084,7 @@ public:
     }
 
     // [counted.iter.access]
-    _NODISCARD constexpr const _Iter& base() const& noexcept /* strengthened */ { // Per LWG-3391
+    _NODISCARD constexpr const _Iter& base() const& noexcept /* strengthened */ {
         return _Current;
     }
 

stl/inc/ranges

@@ -2525,7 +2525,8 @@ namespace ranges {
 
         _NODISCARD constexpr auto begin() {
 #if _CONTAINER_DEBUG_LEVEL > 0
-            _STL_VERIFY(_Pred, "LWG-3490 forbids calling begin on a drop_while_view with no predicate");
+            _STL_VERIFY(
+                _Pred, "N4885 [range.drop.while.view] forbids calling begin on a drop_while_view with no predicate");
 #endif // _CONTAINER_DEBUG_LEVEL > 0
             if constexpr (forward_range<_Vw>) {
                 if (this->_Has_cache()) {
@@ -3776,7 +3777,6 @@ namespace ranges {
             }
 
             constexpr void operator++(int) noexcept(noexcept(++_Current)) /* strengthened */ {
-                // Constraint removed per LWG-3492
                 ++_Current;
             }
 

stl/inc/strstream

@@ -251,7 +251,7 @@ protected:
         const auto _Seeklow  = eback();
         const auto _Seekdist = _Seekhigh - _Seeklow;
 
-        // [depr.strstreambuf.virtuals]/15 effectively says check that the result will be in range
+        // N4727 [depr.strstreambuf.virtuals]/15 effectively says check that the result will be in range
         // [_Seeklow, _Seekhigh]; but we want to calculate this without potential integer overflow
         switch (_Way) {
         case ios_base::beg:

stl/inc/xutility

@@ -3598,7 +3598,6 @@ namespace ranges {
         }
 
         constexpr subrange& advance(const iter_difference_t<_It> _Count) {
-            // Per LWG-3413, this has defined behavior when _Count < 0.
             if constexpr (bidirectional_iterator<_It>) {
                 if (_Count < 0) {
                     _RANGES advance(_First, _Count);
@@ -3762,7 +3761,7 @@ public:
     // clang-format on
 
 #ifdef __cpp_lib_concepts
-    _NODISCARD constexpr const iterator_type& base() const& noexcept /* strengthened */ { // Per LWG-3391
+    _NODISCARD constexpr const iterator_type& base() const& noexcept /* strengthened */ {
         return _Current;
     }
     _NODISCARD constexpr iterator_type base() && noexcept(is_nothrow_move_constructible_v<_Iter>) /* strengthened */ {

tests/std/tests/P0896R4_views_drop_while_death/test.cpp

@@ -21,7 +21,7 @@ void test_view_predicate() {
 
 void test_view_begin() {
     DWV r;
-    (void) r.begin(); // LWG-3490 forbids calling begin on a drop_while_view with no predicate
+    (void) r.begin(); // N4885 [range.drop.while.view] forbids calling begin on a drop_while_view with no predicate
 }
 
 int main(int argc, char* argv[]) {