Path::with_extension: improve examples

Author: tshepang

library/std/src/path.rs

@@ -2743,12 +2743,27 @@ impl Path {
     ///
     /// let path = Path::new("foo.rs");
     /// assert_eq!(path.with_extension("txt"), PathBuf::from("foo.txt"));
+    /// assert_eq!(path.with_extension(""), PathBuf::from("foo"));
+    /// ```
+    ///
+    /// Handling multiple extensions:
+    ///
+    /// ```
+    /// use std::path::{Path, PathBuf};
     ///
     /// let path = Path::new("foo.tar.gz");
-    /// assert_eq!(path.with_extension(""), PathBuf::from("foo.tar"));
     /// assert_eq!(path.with_extension("xz"), PathBuf::from("foo.tar.xz"));
     /// assert_eq!(path.with_extension("").with_extension("txt"), PathBuf::from("foo.txt"));
     /// ```
+    ///
+    /// Adding an extension where one did not exist:
+    ///
+    /// ```
+    /// use std::path::{Path, PathBuf};
+    ///
+    /// let path = Path::new("foo");
+    /// assert_eq!(path.with_extension("rs"), PathBuf::from("foo.rs"));
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_extension<S: AsRef<OsStr>>(&self, extension: S) -> PathBuf {
         self._with_extension(extension.as_ref())