From e1875742d024c9ac52889d26881ca39a2a14cd8e Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Mon, 5 Aug 2019 20:13:59 +0200
Subject: [PATCH] assume_init: warn about valid != safe

---
 src/libcore/mem/maybe_uninit.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/libcore/mem/maybe_uninit.rs b/src/libcore/mem/maybe_uninit.rs
index 64fdf504369f..20367f724b6f 100644
--- a/src/libcore/mem/maybe_uninit.rs
+++ b/src/libcore/mem/maybe_uninit.rs
@@ -402,6 +402,13 @@ impl<T> MaybeUninit<T> {
     ///
     /// [inv]: #initialization-invariant
     ///
+    /// On top of that, remember that most types have additional invariants beyond merely
+    /// being considered initialized at the type level. For example, a `1`-initialized [`Vec<T>`]
+    /// is considered initialized because the only requirement the compiler knows about it
+    /// is that the data pointer must be non-null. Creating such a `Vec<T>` does not cause
+    /// *immediate* undefined behavior, but will cause undefined behavior with most
+    /// safe operations (including dropping it).
+    ///
     /// # Examples
     ///
     /// Correct usage of this method: