1 files changed, 181 insertions, 0 deletions
diff --git a/dev-lang/rust/files/rustc-1.51.0-backport-pr81728.patch b/dev-lang/rust/files/rustc-1.51.0-backport-pr81728.patch
new file mode 100644
index 000000000000..20373f42d307
--- /dev/null
+++ b/dev-lang/rust/files/rustc-1.51.0-backport-pr81728.patch
@@ -0,0 +1,181 @@
+From 70f17ca715d3d7e2fd79cc909b95fd3a6357c13e Mon Sep 17 00:00:00 2001
+From: Yechan Bae <yechan@gatech.edu>
+Date: Wed, 3 Feb 2021 16:36:33 -0500
+Subject: [PATCH 1/2] Fixes #80335
+
+---
+ library/alloc/src/str.rs   | 42 ++++++++++++++++++++++----------------
+ library/alloc/tests/str.rs | 30 +++++++++++++++++++++++++++
+ 2 files changed, 54 insertions(+), 18 deletions(-)
+
+diff --git a/library/alloc/src/str.rs b/library/alloc/src/str.rs
+index 70e0c7dba5ea..a7584c6b6510 100644
+--- a/library/alloc/src/str.rs
++++ b/library/alloc/src/str.rs
+@@ -90,8 +90,8 @@ fn join(slice: &Self, sep: &str) -> String {
+     }
+ }
+ 
+-macro_rules! spezialize_for_lengths {
+-    ($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {
++macro_rules! specialize_for_lengths {
++    ($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {{
+         let mut target = $target;
+         let iter = $iter;
+         let sep_bytes = $separator;
+@@ -102,7 +102,8 @@ macro_rules! spezialize_for_lengths {
+                 $num => {
+                     for s in iter {
+                         copy_slice_and_advance!(target, sep_bytes);
+-                        copy_slice_and_advance!(target, s.borrow().as_ref());
++                        let content_bytes = s.borrow().as_ref();
++                        copy_slice_and_advance!(target, content_bytes);
+                     }
+                 },
+             )*
+@@ -110,11 +111,13 @@ macro_rules! spezialize_for_lengths {
+                 // arbitrary non-zero size fallback
+                 for s in iter {
+                     copy_slice_and_advance!(target, sep_bytes);
+-                    copy_slice_and_advance!(target, s.borrow().as_ref());
++                    let content_bytes = s.borrow().as_ref();
++                    copy_slice_and_advance!(target, content_bytes);
+                 }
+             }
+         }
+-    };
++        target
++    }}
+ }
+ 
+ macro_rules! copy_slice_and_advance {
+@@ -153,7 +156,7 @@ fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
+     // if the `len` calculation overflows, we'll panic
+     // we would have run out of memory anyway and the rest of the function requires
+     // the entire Vec pre-allocated for safety
+-    let len = sep_len
++    let reserved_len = sep_len
+         .checked_mul(iter.len())
+         .and_then(|n| {
+             slice.iter().map(|s| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
+@@ -161,22 +164,25 @@ fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
+         .expect("attempt to join into collection with len > usize::MAX");
+ 
+     // crucial for safety
+-    let mut result = Vec::with_capacity(len);
+-    assert!(result.capacity() >= len);
++    let mut result = Vec::with_capacity(reserved_len);
++    debug_assert!(result.capacity() >= reserved_len);
+ 
+     result.extend_from_slice(first.borrow().as_ref());
+ 
+     unsafe {
+-        {
+-            let pos = result.len();
+-            let target = result.get_unchecked_mut(pos..len);
+-
+-            // copy separator and slices over without bounds checks
+-            // generate loops with hardcoded offsets for small separators
+-            // massive improvements possible (~ x2)
+-            spezialize_for_lengths!(sep, target, iter; 0, 1, 2, 3, 4);
+-        }
+-        result.set_len(len);
++        let pos = result.len();
++        let target = result.get_unchecked_mut(pos..reserved_len);
++
++        // copy separator and slices over without bounds checks
++        // generate loops with hardcoded offsets for small separators
++        // massive improvements possible (~ x2)
++        let remain = specialize_for_lengths!(sep, target, iter; 0, 1, 2, 3, 4);
++
++        // issue #80335: A weird borrow implementation can return different
++        // slices for the length calculation and the actual copy, so
++        // `remain.len()` might be non-zero.
++        let result_len = reserved_len - remain.len();
++        result.set_len(result_len);
+     }
+     result
+ }
+diff --git a/library/alloc/tests/str.rs b/library/alloc/tests/str.rs
+index 604835e6cc4a..6df8d8c2f354 100644
+--- a/library/alloc/tests/str.rs
++++ b/library/alloc/tests/str.rs
+@@ -160,6 +160,36 @@ fn test_join_for_different_lengths_with_long_separator() {
+     test_join!("～～～～～a～～～～～bc", ["", "a", "bc"], "～～～～～");
+ }
+ 
++#[test]
++fn test_join_isue_80335() {
++    use core::{borrow::Borrow, cell::Cell};
++
++    struct WeirdBorrow {
++        state: Cell<bool>,
++    }
++
++    impl Default for WeirdBorrow {
++        fn default() -> Self {
++            WeirdBorrow { state: Cell::new(false) }
++        }
++    }
++
++    impl Borrow<str> for WeirdBorrow {
++        fn borrow(&self) -> &str {
++            let state = self.state.get();
++            if state {
++                "0"
++            } else {
++                self.state.set(true);
++                "123456"
++            }
++        }
++    }
++
++    let arr: [WeirdBorrow; 3] = Default::default();
++    test_join!("0-0-0", arr, "-");
++}
++
+ #[test]
+ #[cfg_attr(miri, ignore)] // Miri is too slow
+ fn test_unsafe_slice() {
+-- 
+2.31.1
+
+
+From 10020817d2e6756be1ff2ac3c182af97cf7fe904 Mon Sep 17 00:00:00 2001
+From: Yechan Bae <yechan@gatech.edu>
+Date: Sat, 20 Mar 2021 13:42:54 -0400
+Subject: [PATCH 2/2] Update the comment
+
+---
+ library/alloc/src/str.rs | 8 ++++----
+ 1 file changed, 4 insertions(+), 4 deletions(-)
+
+diff --git a/library/alloc/src/str.rs b/library/alloc/src/str.rs
+index a7584c6b6510..4d1e876457b8 100644
+--- a/library/alloc/src/str.rs
++++ b/library/alloc/src/str.rs
+@@ -163,7 +163,7 @@ fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
+         })
+         .expect("attempt to join into collection with len > usize::MAX");
+ 
+-    // crucial for safety
++    // prepare an uninitialized buffer
+     let mut result = Vec::with_capacity(reserved_len);
+     debug_assert!(result.capacity() >= reserved_len);
+ 
+@@ -178,9 +178,9 @@ fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
+         // massive improvements possible (~ x2)
+         let remain = specialize_for_lengths!(sep, target, iter; 0, 1, 2, 3, 4);
+ 
+-        // issue #80335: A weird borrow implementation can return different
+-        // slices for the length calculation and the actual copy, so
+-        // `remain.len()` might be non-zero.
++        // A weird borrow implementation may return different
++        // slices for the length calculation and the actual copy.
++        // Make sure we don't expose uninitialized bytes to the caller.
+         let result_len = reserved_len - remain.len();
+         result.set_len(result_len);
+     }
+-- 
+2.31.1
+