test: added tests for const-ness

Author: conradludgate

library/std/src/ffi/os_str.rs

@@ -629,7 +629,18 @@ impl OsStr {
         s.as_ref()
     }
 
-    /// Creates a new `OsStr` from a `str`.
+    /// Creates a new [`OsStr`] from a [`str`].
+    ///
+    /// This method supports const expressions. However, if you don't need const,
+    /// you should probably use the [`OsStr::new`] method instead.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::ffi::OsStr;
+    ///
+    /// const OS_STR: OsStr = OsStr::from_str("foo");
+    /// ```
     #[inline]
     #[unstable(feature = "const_path", reason = "TBD", issue = "none")]
     pub const fn from_str(s: &str) -> &OsStr {

library/std/src/ffi/os_str/tests.rs

@@ -163,3 +163,10 @@ fn into_rc() {
     assert_eq!(&*rc2, os_str);
     assert_eq!(&*arc2, os_str);
 }
+
+#[test]
+pub fn test_const() {
+    const STR: &str = "/foo/bar";
+    const OS_STR: &OsStr = OsStr::from_str(STR);
+    assert_eq!(OS_STR, OsStr::new(STR));
+}

library/std/src/path.rs

@@ -1951,12 +1951,19 @@ impl Path {
         Self::from_os_str(s.as_ref())
     }
 
-    /// Creates a new `Path` from an `OsStr`.
+    /// Creates a new [`Path`] from an [`OsStr`].
     ///
-    /// This is a cost-free conversion.
+    /// This method supports const expressions. However, if you don't need const,
+    /// you should probably use the [`Path::new`] method instead.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::ffi::OsStr;
+    /// use std::path::Path;
     ///
-    /// You should probably use the [`Path::new`] method instead,
-    /// however, this method supports const expressions
+    /// const PATH: Path = Path::from_os_str(OsStr::from_str("/foo/bar"));
+    /// ```
     #[inline]
     #[unstable(feature = "const_path", reason = "TBD", issue = "none")]
     pub const fn from_os_str(s: &OsStr) -> &Path {

library/std/src/path/tests.rs

@@ -1665,6 +1665,13 @@ fn test_ord() {
     ord!(Equal, "foo/bar", "foo/bar//");
 }
 
+#[test]
+pub fn test_const() {
+    const STR: &str = "/foo/bar";
+    const PATH: &Path = Path::from_os_str(OsStr::from_str(STR));
+    assert_eq!(PATH, Path::new(STR));
+}
+
 #[bench]
 fn bench_path_cmp_fast_path_buf_sort(b: &mut test::Bencher) {
     let prefix = "my/home";