Fix Rust wdirname and wbasename and port the C++ tests

These functions were rather buggy; add tests and fix the test failures.

fish-rust/src/wutil/mod.rs

@@ -327,12 +327,12 @@ pub fn wdirname(mut path: WString) -> WString {
     // This follows OpenGroup dirname recipe.
 
     // 1: Double-slash stays.
-    if path == "//"L {
+    if path == "//" {
         return path;
     }
 
     // 2: All slashes => return slash.
-    if !path.is_empty() && path.chars().find(|c| *c == '/').is_none() {
+    if !path.is_empty() && path.chars().all(|c| c == '/') {
         return "/"L.to_owned();
     }
 
@@ -342,7 +342,7 @@ pub fn wdirname(mut path: WString) -> WString {
     }
 
     // 4: No slashes left => return period.
-    let Some(last_slash) = path.chars().rev().position(|c| c == '/') else {
+    let Some(last_slash) = path.chars().rposition(|c| c == '/') else {
         return "."L.to_owned()
     };
 
@@ -373,19 +373,18 @@ pub fn wbasename(mut path: WString) -> WString {
 
     // 2: Skip as permitted.
     // 3: All slashes => return slash.
-    if !path.is_empty() && path.chars().find(|c| *c == '/').is_none() {
+    if !path.is_empty() && path.chars().all(|c| c == '/') {
         return "/"L.to_owned();
     }
 
     // 4: Remove trailing slashes.
-    // while (!path.is_empty() && path.back() == '/') path.pop_back();
     while path.as_char_slice().last() == Some(&'/') {
         path.pop();
     }
 
     // 5: Remove up to and including last slash.
-    if let Some(last_slash) = path.chars().rev().position(|c| c == '/') {
+    if let Some(last_slash) = path.chars().rposition(|c| c == '/') {
-        path.truncate(last_slash + 1);
+        path.replace_range(..last_slash + 1, ""L);
     };
     path
 }
@@ -871,3 +870,53 @@ fn test_wstr_offset_in() {
     assert_eq!(wstr_offset_in(&base[6..], &base[6..]), 0);
     assert_eq!(wstr_offset_in(&base[base.len()..], base), base.len());
 }
+
+#[test]
+#[widestrs]
+fn test_wdirname_wbasename() {
+    // path, dir, base
+    struct Test(&'static wstr, &'static wstr, &'static wstr);
+    const testcases: &[Test] = &[
+        Test(""L, "."L, "."L),
+        Test("foo//"L, "."L, "foo"L),
+        Test("foo//////"L, "."L, "foo"L),
+        Test("/////foo"L, "/"L, "foo"L),
+        Test("//foo/////bar"L, "//foo"L, "bar"L),
+        Test("foo/////bar"L, "foo"L, "bar"L),
+        // Examples given in XPG4.2.
+        Test("/usr/lib"L, "/usr"L, "lib"L),
+        Test("usr"L, "."L, "usr"L),
+        Test("/"L, "/"L, "/"L),
+        Test("."L, "."L, "."L),
+        Test(".."L, "."L, ".."L),
+    ];
+
+    for tc in testcases {
+        let Test(path, tc_dir, tc_base) = *tc;
+        let dir = wdirname(path.to_owned());
+        assert_eq!(
+            dir, tc_dir,
+            "\npath: {:?}, dir: {:?}, tc.dir: {:?}",
+            path, dir, tc_dir
+        );
+
+        let base = wbasename(path.to_owned());
+        assert_eq!(
+            base, tc_base,
+            "\npath: {:?}, base: {:?}, tc.base: {:?}",
+            path, base, tc_base
+        );
+    }
+
+    // Ensure strings which greatly exceed PATH_MAX still work (#7837).
+    const PATH_MAX: usize = libc::PATH_MAX as usize;
+    let mut longpath = WString::new();
+    longpath.reserve(PATH_MAX * 2 + 10);
+    while longpath.char_count() <= PATH_MAX * 2 {
+        longpath.push_str("/overlong");
+    }
+    let last_slash = longpath.chars().rposition(|c| c == '/').unwrap();
+    let longpath_dir = &longpath[..last_slash];
+    assert_eq!(wdirname(longpath.clone()), longpath_dir);
+    assert_eq!(wbasename(longpath), "overlong"L);
+}