From ea24395617745dd0483a7c4114da04b114a7d3d8 Mon Sep 17 00:00:00 2001
From: Mara Bos <m-ou.se@m-ou.se>
Date: Tue, 20 Oct 2020 20:20:06 +0200
Subject: [PATCH] Add debug_asserts for the unsafe indexing in fmt::write.

---
 library/core/src/fmt/mod.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
index 04edf4611ecc..cc84bf14a33a 100644
--- a/library/core/src/fmt/mod.rs
+++ b/library/core/src/fmt/mod.rs
@@ -1110,7 +1110,7 @@ unsafe fn run(fmt: &mut Formatter<'_>, arg: &rt::v1::Argument, args: &[ArgumentV
     }
 
     // Extract the correct argument
-
+    debug_assert!(arg.position < args.len());
     // SAFETY: arg and args come from the same Arguments,
     // which guarantees its index is always within bounds.
     let value = unsafe { args.get_unchecked(arg.position) };
@@ -1124,6 +1124,7 @@ unsafe fn getcount(args: &[ArgumentV1<'_>], cnt: &rt::v1::Count) -> Option<usize
         rt::v1::Count::Is(n) => Some(n),
         rt::v1::Count::Implied => None,
         rt::v1::Count::Param(i) => {
+            debug_assert!(i < args.len());
             // SAFETY: cnt and args come from the same Arguments,
             // which guarantees this index is always within bounds.
             unsafe { args.get_unchecked(i).as_usize() }