From bd640d10e638d82458f9e79b80e68147eeb12bf9 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 2 Sep 2023 12:51:52 -0700
Subject: [PATCH 1/2] Remove unsafe code from AsDisplay

---
 src/display.rs             | 47 ++++++++++++++++----------------------
 tests/ui/no-display.stderr |  2 +-
 2 files changed, 21 insertions(+), 28 deletions(-)

diff --git a/src/display.rs b/src/display.rs
index 2b0ba5a..e765c18 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -2,52 +2,45 @@ use std::fmt::{self, Display};
 use std::path::{Path, PathBuf};
 
 #[doc(hidden)]
-pub trait AsDisplay {
-    type Target: Display + ?Sized;
+pub trait AsDisplay<'a> {
+    type Target: Display;
 
-    fn as_display(&self) -> &Self::Target;
+    fn as_display(&'a self) -> Self::Target;
 }
 
-impl<T: Display> AsDisplay for &T {
-    type Target = T;
+impl<'a, T> AsDisplay<'a> for &T
+where
+    T: Display + 'a,
+{
+    type Target = &'a T;
 
-    fn as_display(&self) -> &Self::Target {
-        self
+    fn as_display(&'a self) -> Self::Target {
+        *self
     }
 }
 
-impl AsDisplay for Path {
-    type Target = PathDisplay;
+impl<'a> AsDisplay<'a> for Path {
+    type Target = PathDisplay<'a>;
 
     #[inline]
-    fn as_display(&self) -> &Self::Target {
-        PathDisplay::new(self)
+    fn as_display(&'a self) -> Self::Target {
+        PathDisplay(self)
     }
 }
 
-impl AsDisplay for PathBuf {
-    type Target = PathDisplay;
+impl<'a> AsDisplay<'a> for PathBuf {
+    type Target = PathDisplay<'a>;
 
     #[inline]
-    fn as_display(&self) -> &Self::Target {
-        PathDisplay::new(self.as_path())
+    fn as_display(&'a self) -> Self::Target {
+        PathDisplay(self.as_path())
     }
 }
 
 #[doc(hidden)]
-#[repr(transparent)]
-pub struct PathDisplay(Path);
+pub struct PathDisplay<'a>(&'a Path);
 
-impl PathDisplay {
-    #[inline]
-    fn new(path: &Path) -> &Self {
-        // SAFETY: PathDisplay is repr(transparent) so casting pointers between
-        // it and its payload is safe.
-        unsafe { &*(path as *const Path as *const Self) }
-    }
-}
-
-impl Display for PathDisplay {
+impl<'a> Display for PathDisplay<'a> {
     #[inline]
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
         self.0.display().fmt(formatter)
diff --git a/tests/ui/no-display.stderr b/tests/ui/no-display.stderr
index 26dc842..0f47c24 100644
--- a/tests/ui/no-display.stderr
+++ b/tests/ui/no-display.stderr
@@ -9,7 +9,7 @@ error[E0599]: the method `as_display` exists for reference `&NoDisplay`, but its
   |
   = note: the following trait bounds were not satisfied:
           `NoDisplay: std::fmt::Display`
-          which is required by `&NoDisplay: AsDisplay`
+          which is required by `&NoDisplay: AsDisplay<'_>`
 note: the trait `std::fmt::Display` must be implemented
  --> $RUST/core/src/fmt/mod.rs
   |

From bb49bb3fa80fc12250c19a75ac5c5cf6e44c2603 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 2 Sep 2023 13:01:50 -0700
Subject: [PATCH 2/2] Delete PathDisplay type

---
 src/display.rs | 22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/src/display.rs b/src/display.rs
index e765c18..58d11e4 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -1,5 +1,5 @@
-use std::fmt::{self, Display};
-use std::path::{Path, PathBuf};
+use std::fmt::Display;
+use std::path::{self, Path, PathBuf};
 
 #[doc(hidden)]
 pub trait AsDisplay<'a> {
@@ -20,29 +20,19 @@ where
 }
 
 impl<'a> AsDisplay<'a> for Path {
-    type Target = PathDisplay<'a>;
+    type Target = path::Display<'a>;
 
     #[inline]
     fn as_display(&'a self) -> Self::Target {
-        PathDisplay(self)
+        self.display()
     }
 }
 
 impl<'a> AsDisplay<'a> for PathBuf {
-    type Target = PathDisplay<'a>;
+    type Target = path::Display<'a>;
 
     #[inline]
     fn as_display(&'a self) -> Self::Target {
-        PathDisplay(self.as_path())
-    }
-}
-
-#[doc(hidden)]
-pub struct PathDisplay<'a>(&'a Path);
-
-impl<'a> Display for PathDisplay<'a> {
-    #[inline]
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-        self.0.display().fmt(formatter)
+        self.display()
     }
 }