Avoid allocations in Debug for os_str

Fixes #38879

3 files changed, 59 insertions, 21 deletions

diff --git a/src/libstd/sys/redox/os_str.rs b/src/libstd/sys/redox/os_str.rs
index c2bba07f68c..c54286353a9 100644
--- a/src/libstd/sys/redox/os_str.rs
+++ b/src/libstd/sys/redox/os_str.rs
@@ -12,10 +12,11 @@
 /// a `Vec<u8>`/`[u8]`.
 
 use borrow::Cow;
-use fmt::{self, Debug};
+use fmt;
 use str;
 use mem;
 use sys_common::{AsInner, IntoInner};
+use std_unicode::lossy::Utf8Lossy;
 
 #[derive(Clone, Hash)]
 pub struct Buf {
@@ -26,15 +27,27 @@ pub struct Slice {
     pub inner: [u8]
 }
 
-impl Debug for Slice {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        self.to_string_lossy().fmt(formatter)
+impl fmt::Debug for Slice {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&Utf8Lossy::from_bytes(&self.inner), formatter)
     }
 }
 
-impl Debug for Buf {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        self.as_slice().fmt(formatter)
+impl fmt::Display for Slice {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&Utf8Lossy::from_bytes(&self.inner), formatter)
+    }
+}
+
+impl fmt::Debug for Buf {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(self.as_slice(), formatter)
+    }
+}
+
+impl fmt::Display for Buf {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self.as_slice(), formatter)
     }
 }
 
diff --git a/src/libstd/sys/unix/os_str.rs b/src/libstd/sys/unix/os_str.rs
index f5b942d3343..777db17e3e1 100644
--- a/src/libstd/sys/unix/os_str.rs
+++ b/src/libstd/sys/unix/os_str.rs
@@ -12,10 +12,11 @@
 /// a `Vec<u8>`/`[u8]`.
 
 use borrow::Cow;
-use fmt::{self, Debug};
+use fmt;
 use str;
 use mem;
 use sys_common::{AsInner, IntoInner};
+use std_unicode::lossy::Utf8Lossy;
 
 #[derive(Clone, Hash)]
 pub struct Buf {
@@ -26,15 +27,27 @@ pub struct Slice {
     pub inner: [u8]
 }
 
-impl Debug for Slice {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        self.to_string_lossy().fmt(formatter)
+impl fmt::Debug for Slice {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&Utf8Lossy::from_bytes(&self.inner), formatter)
     }
 }
 
-impl Debug for Buf {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        self.as_slice().fmt(formatter)
+impl fmt::Display for Slice {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&Utf8Lossy::from_bytes(&self.inner), formatter)
+    }
+}
+
+impl fmt::Debug for Buf {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(self.as_slice(), formatter)
+    }
+}
+
+impl fmt::Display for Buf {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self.as_slice(), formatter)
     }
 }
 
diff --git a/src/libstd/sys/windows/os_str.rs b/src/libstd/sys/windows/os_str.rs
index f401e7b35c8..3eb4582718b 100644
--- a/src/libstd/sys/windows/os_str.rs
+++ b/src/libstd/sys/windows/os_str.rs
@@ -12,7 +12,7 @@
 /// wrapper around the "WTF-8" encoding; see the `wtf8` module for more.
 
 use borrow::Cow;
-use fmt::{self, Debug};
+use fmt;
 use sys_common::wtf8::{Wtf8, Wtf8Buf};
 use mem;
 use sys_common::{AsInner, IntoInner};
@@ -34,9 +34,15 @@ impl AsInner<Wtf8> for Buf {
     }
 }
 
-impl Debug for Buf {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        self.as_slice().fmt(formatter)
+impl fmt::Debug for Buf {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(self.as_slice(), formatter)
+    }
+}
+
+impl fmt::Display for Buf {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self.as_slice(), formatter)
     }
 }
 
@@ -44,9 +50,15 @@ pub struct Slice {
     pub inner: Wtf8
 }
 
-impl Debug for Slice {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        self.inner.fmt(formatter)
+impl fmt::Debug for Slice {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.inner, formatter)
+    }
+}
+
+impl fmt::Display for Slice {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&self.inner, formatter)
     }
 }