Add links to std::char::REPLACEMENT_CHARACTER from docs.

There are a few places where we mention the replacement character in the
docs, and it could be helpful for users to utilize the constant which is
available in the standard library, so let’s link to it!

4 files changed, 12 insertions, 6 deletions

diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index b2777f5c485..2b87094926c 100644
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -1175,9 +1175,9 @@ impl CStr {
     /// If the contents of the `CStr` are valid UTF-8 data, this
     /// function will return a [`Cow`]`::`[`Borrowed`]`(`[`&str`]`)`
     /// with the the corresponding [`&str`] slice. Otherwise, it will
-    /// replace any invalid UTF-8 sequences with `U+FFFD REPLACEMENT
-    /// CHARACTER` and return a [`Cow`]`::`[`Owned`]`(`[`String`]`)`
-    /// with the result.
+    /// replace any invalid UTF-8 sequences with
+    /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD] and return a
+    /// [`Cow`]`::`[`Owned`]`(`[`String`]`)` with the result.
     ///
     /// > **Note**: This method is currently implemented to check for validity
     /// > after a constant-time cast, but it is planned to alter its definition
@@ -1189,6 +1189,7 @@ impl CStr {
     /// [`Owned`]: ../borrow/enum.Cow.html#variant.Owned
     /// [`str`]: ../primitive.str.html
     /// [`String`]: ../string/struct.String.html
+    /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
     ///
     /// # Examples
     ///
diff --git a/src/libstd/ffi/os_str.rs b/src/libstd/ffi/os_str.rs
index 9e501a84e05..6bcd62dbd59 100644
--- a/src/libstd/ffi/os_str.rs
+++ b/src/libstd/ffi/os_str.rs
@@ -520,10 +520,12 @@ impl OsStr {
 
     /// Converts an `OsStr` to a [`Cow`]`<`[`str`]`>`.
     ///
-    /// Any non-Unicode sequences are replaced with U+FFFD REPLACEMENT CHARACTER.
+    /// Any non-Unicode sequences are replaced with
+    /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD].
     ///
     /// [`Cow`]: ../../std/borrow/enum.Cow.html
     /// [`str`]: ../../std/primitive.str.html
+    /// [U+FFFD]: ../../std/char/constant.REPLACEMENT_CHARACTER.html
     ///
     /// # Examples
     ///
diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index 688a7e99f10..ca8be75fab5 100644
--- a/src/libstd/path.rs
+++ b/src/libstd/path.rs
@@ -1737,9 +1737,11 @@ impl Path {
 
     /// Converts a `Path` to a [`Cow<str>`].
     ///
-    /// Any non-Unicode sequences are replaced with U+FFFD REPLACEMENT CHARACTER.
+    /// Any non-Unicode sequences are replaced with
+    /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD].
     ///
     /// [`Cow<str>`]: ../borrow/enum.Cow.html
+    /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
     ///
     /// # Examples
     ///
diff --git a/src/libstd/sys/windows/ext/ffi.rs b/src/libstd/sys/windows/ext/ffi.rs
index 98d43552489..bae0d02786a 100644
--- a/src/libstd/sys/windows/ext/ffi.rs
+++ b/src/libstd/sys/windows/ext/ffi.rs
@@ -31,7 +31,7 @@
 //!
 //! If Rust code *does* need to look into those strings, it can
 //! convert them to valid UTF-8, possibly lossily, by substituting
-//! invalid sequences with U+FFFD REPLACEMENT CHARACTER, as is
+//! invalid sequences with [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], as is
 //! conventionally done in other Rust APIs that deal with string
 //! encodings.
 //!
@@ -65,6 +65,7 @@
 //! [`from_wide`]: trait.OsStringExt.html#tymethod.from_wide
 //! [`encode_wide`]: trait.OsStrExt.html#tymethod.encode_wide
 //! [`collect`]: ../../../iter/trait.Iterator.html#method.collect
+//! [U+FFFD]: ../../../char/constant.REPLACEMENT_CHARACTER.html
 
 #![stable(feature = "rust1", since = "1.0.0")]