Auto merge of #64160 - Centril:rollup-vrfj1pt, r=Centril

Rollup of 15 pull requests

Successful merges:

 - #62860 (Stabilize checked_duration_since for 1.38.0)
 - #63549 (Rev::rposition counts from the wrong end)
 - #63985 (Stabilize pin_into_inner in 1.39.0)
 - #64005 (Add a `Place::is_indirect` method to determine whether a `Place` contains a `Deref` projection)
 - #64031 (Harden `param_attrs` test wrt. usage of a proc macro `#[attr]`)
 - #64038 (Check impl trait substs when checking for recursive types)
 - #64043 (Add some more tests for underscore imports)
 - #64092 (Update xLTO compatibility table in rustc book.)
 - #64110 (Refer to "`self` type" instead of "receiver type")
 - #64120 (Move path parsing earlier)
 - #64123 (Added warning around code with reference to uninit bytes)
 - #64128 (unused_parens: account for or-patterns and `&(mut x)`)
 - #64141 (Minimize uses of `LocalInternedString`)
 - #64142 (Fix doc links in `std::cmp` module)
 - #64148 (fix a few typos in comments)

Failed merges:

r? @ghost

1 files changed, 8 insertions, 0 deletions

diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index 5060f368229..0386dbd490d 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -371,6 +371,14 @@ where
     loop {
         if g.len == g.buf.len() {
             unsafe {
+                // FIXME(danielhenrymantilla): #42788
+                //
+                //   - This creates a (mut) reference to a slice of
+                //     _uninitialized_ integers, which is **undefined behavior**
+                //
+                //   - Only the standard library gets to soundly "ignore" this,
+                //     based on its privileged knowledge of unstable rustc
+                //     internals;
                 g.buf.reserve(reservation_size(r));
                 let capacity = g.buf.capacity();
                 g.buf.set_len(capacity);