From 64c8e662a0b6e4ad3b44ad4288349c208a25cd1c Mon Sep 17 00:00:00 2001
From: Elias Holzmann <9659253+EliasHolzmann@users.noreply.github.com>
Date: Mon, 27 Nov 2023 03:31:29 +0100
Subject: [PATCH] Formatter::with_options: Use different lifetimes

Formatter::with_options takes self as a mutable reference (`&'a mut
Formatter<'b>`). `'a` and `'b` need to be different lifetimes. Just taking `&'a
mut Formatter<'a>` and trusting in Rust being able to implicitely convert from
`&'a mut Formatter<'b>` if necessary (after all, `'a` must be smaller than `'b`
anyway) fails because `'b` is behind a *mutable* reference. For background on
on this behavior, see https://doc.rust-lang.org/nomicon/subtyping.html#variance.
---
 core/src/fmt/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/src/fmt/mod.rs b/core/src/fmt/mod.rs
index 8e08b7fe983df..a5c0e1ce4e30d 100644
--- a/core/src/fmt/mod.rs
+++ b/core/src/fmt/mod.rs
@@ -530,7 +530,7 @@ impl<'a> Formatter<'a> {
 
     /// Creates a new formatter based on this one with given [`FormattingOptions`].
     #[unstable(feature = "formatting_options", issue = "118117")]
-    pub fn with_options(&'a mut self, options: FormattingOptions) -> Self {
+    pub fn with_options<'b>(&'b mut self, options: FormattingOptions) -> Formatter<'b> {
         Formatter { options, buf: self.buf }
     }
 }