Unix path::absolute: Fix leading "." component

Testing leading `.` and `..` components were missing from the unix tests.

Author: ChrisDenton

library/std/src/path/tests.rs

@@ -1719,6 +1719,11 @@ fn test_unix_absolute() {
     assert_eq!(absolute("///a/b/c").unwrap(), Path::new("/a/b/c"));
     assert_eq!(absolute("/a/b/c/").unwrap(), Path::new("/a/b/c/"));
     assert_eq!(absolute("/a/./b/../c/.././..").unwrap(), Path::new("/a/b/../c/../.."));
+
+    // Test leading `.` and `..` components
+    let curdir = crate::env::current_dir().unwrap();
+    assert_eq!(absolute("./a").unwrap().as_os_str(), curdir.join("a").as_os_str());
+    assert_eq!(absolute("../a").unwrap().as_os_str(), curdir.join("../a").as_os_str()); // return /pwd/../a
 }
 
 #[test]

library/std/src/sys/unix/path.rs

@@ -28,7 +28,8 @@ pub(crate) fn absolute(path: &Path) -> io::Result<PathBuf> {
     // See 4.13 Pathname Resolution, IEEE Std 1003.1-2017
     // https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13
 
-    let mut components = path.components();
+    // Get the components, skipping the redundant leading "." component if it exists.
+    let mut components = path.strip_prefix(".").unwrap_or(path).components();
     let path_os = path.as_os_str().bytes();
 
     let mut normalized = if path.is_absolute() {