From 8e8e27376c060f5e0e8beb8c0827fe752d021890 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Fri, 8 Nov 2024 12:18:53 -0500
Subject: [PATCH 1/2] Add test of dynamically sized error type

    error[E0599]: the method `as_display` exists for reference `&str`, but its trait bounds were not satisfied
      --> tests/test_path.rs:26:9
       |
    26 | #[error("{tail}")]
       |         ^^^^^^^^ method cannot be called on `&str` due to unsatisfied trait bounds
       |
       = note: the following trait bounds were not satisfied:
               `str: Sized`
               which is required by `&str: AsDisplay<'_>`
---
 tests/test_path.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tests/test_path.rs b/tests/test_path.rs
index f054077..16881ae 100644
--- a/tests/test_path.rs
+++ b/tests/test_path.rs
@@ -22,6 +22,13 @@ enum EnumPathBuf {
     Read(PathBuf),
 }
 
+#[derive(Error, Debug)]
+#[error("{tail}")]
+pub struct UnsizedError {
+    pub head: i32,
+    pub tail: str,
+}
+
 fn assert<T: Display>(expected: &str, value: T) {
     assert_eq!(expected, value.to_string());
 }

From 24c04daea901b7a426db8fca2c743d0253986ab3 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Fri, 8 Nov 2024 12:19:52 -0500
Subject: [PATCH 2/2] Support dynamically sized field in error

---
 src/display.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/display.rs b/src/display.rs
index 7ccdd81..7b2bf1c 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -13,7 +13,7 @@ pub trait AsDisplay<'a>: Sealed {
 
 impl<'a, T> AsDisplay<'a> for &T
 where
-    T: Display + 'a,
+    T: Display + ?Sized + 'a,
 {
     type Target = &'a T;
 
@@ -44,7 +44,7 @@ impl<'a> AsDisplay<'a> for PathBuf {
 
 #[doc(hidden)]
 pub trait Sealed {}
-impl<T: Display> Sealed for &T {}
+impl<T: Display + ?Sized> Sealed for &T {}
 #[cfg(feature = "std")]
 impl Sealed for Path {}
 #[cfg(feature = "std")]