From 11e79084845a78e2421ea3abafe0de5a54ca2bde Mon Sep 17 00:00:00 2001
From: Martin Leitner-Ankerl <martin.ankerl@gmail.com>
Date: Sun, 24 Apr 2022 12:55:57 +0200
Subject: [PATCH] prevector: only allow trivially copyable types

The prevector implementation currently can't be used with types that are
not trivially copyable, due to the use of memmove. Trivially copyable
implies that it is trivially destructible, see
https://eel.is/c++draft/class.prop#1.3

That means that the checks for std::is_trivially_destructible are not
necessary, and in fact where used it wouldn't be enough. E.g. in
`erase(iterator, iterator)` the elements in range first-last are destructed,
but it does not destruct elements left after `memmove`.

This commit removes the checks for `std::is_trivially_destructible`
and instead adds a `static_assert(std::is_trivially_copyable_v<T>);` to
make sure `prevector` is only used with supported types.
---
 src/prevector.h | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/src/prevector.h b/src/prevector.h
index aa20efaaa7..fe8339eb8b 100644
--- a/src/prevector.h
+++ b/src/prevector.h
@@ -35,6 +35,8 @@
  */
 template<unsigned int N, typename T, typename Size = uint32_t, typename Diff = int32_t>
 class prevector {
+    static_assert(std::is_trivially_copyable_v<T>);
+
 public:
     typedef Size size_type;
     typedef Diff difference_type;
@@ -411,15 +413,7 @@ public:
         // representation (with capacity N and size <= N).
         iterator p = first;
         char* endp = (char*)&(*end());
-        if (!std::is_trivially_destructible<T>::value) {
-            while (p != last) {
-                (*p).~T();
-                _size--;
-                ++p;
-            }
-        } else {
-            _size -= last - p;
-        }
+        _size -= last - p;
         memmove(&(*first), &(*last), endp - ((char*)(&(*last))));
         return first;
     }
@@ -464,9 +458,6 @@ public:
     }
 
     ~prevector() {
-        if (!std::is_trivially_destructible<T>::value) {
-            clear();
-        }
         if (!is_direct()) {
             free(_union.indirect_contents.indirect);
             _union.indirect_contents.indirect = nullptr;