refactor(dirname): implement pure string manipulation per POSIX

src/uu/dirname/src/dirname.rs

@@ -5,7 +5,6 @@
 
 use clap::{Arg, ArgAction, Command};
 use std::ffi::OsString;
-use std::path::Path;
 use uucore::display::print_verbatim;
 use uucore::error::{UResult, UUsageError};
 use uucore::format_usage;
@@ -18,51 +17,84 @@ mod options {
     pub const DIR: &str = "dir";
 }
 
-/// Handle the special case where a path ends with "/."
+/// Perform dirname as pure string manipulation per POSIX/GNU behavior.
+///
+/// dirname should NOT normalize paths. It does simple string manipulation:
+/// 1. Strip trailing slashes (unless path is all slashes)
+/// 2. If ends with `/.` (possibly `//.` or `///.`), strip the `/+.` pattern
+/// 3. Otherwise, remove everything after the last `/`
+/// 4. If no `/` found, return `.`
+/// 5. Strip trailing slashes from result (unless result would be empty)
+///
+/// Examples:
+/// - `foo/.` → `foo`
+/// - `foo/./bar` → `foo/.`
+/// - `foo/bar` → `foo`
+/// - `a/b/c` → `a/b`
 ///
-/// This matches GNU/POSIX behavior where `dirname("/home/dos/.")` returns "/home/dos"
-/// rather than "/home" (which would be the result of `Path::parent()` due to normalization).
 /// Per POSIX.1-2017 dirname specification and GNU coreutils manual:
 /// - POSIX: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/dirname.html>
 /// - GNU: <https://www.gnu.org/software/coreutils/manual/html_node/dirname-invocation.html>
 ///
-/// dirname should do simple string manipulation without path normalization.
 /// See issue #8910 and similar fix in basename (#8373, commit c5268a897).
-///
-/// Returns `Some(())` if the special case was handled (output already printed),
-/// or `None` if normal `Path::parent()` logic should be used.
-fn handle_trailing_dot(path_bytes: &[u8]) -> Option<()> {
-    if !path_bytes.ends_with(b"/.") {
-        return None;
+fn dirname_string_manipulation(path_bytes: &[u8]) -> Vec<u8> {
+    if path_bytes.is_empty() {
+        return b".".to_vec();
     }
 
-    // Strip the "/." suffix and print the result
-    if path_bytes.len() == 2 {
-        // Special case: "/." -> "/"
-        print!("/");
-        Some(())
-    } else {
-        // General case: "/home/dos/." -> "/home/dos"
-        let stripped = &path_bytes[..path_bytes.len() - 2];
-        #[cfg(unix)]
-        {
-            use std::os::unix::ffi::OsStrExt;
-            let result = std::ffi::OsStr::from_bytes(stripped);
-            print_verbatim(result).unwrap();
-            Some(())
-        }
-        #[cfg(not(unix))]
-        {
-            // On non-Unix, fall back to lossy conversion
-            if let Ok(s) = std::str::from_utf8(stripped) {
-                print!("{s}");
-                Some(())
-            } else {
-                // Can't handle non-UTF-8 on non-Unix, fall through to normal logic
-                None
+    let mut bytes = path_bytes;
+
+    // Step 1: Strip trailing slashes (but not if the entire path is slashes)
+    let all_slashes = bytes.iter().all(|&b| b == b'/');
+    if all_slashes {
+        return b"/".to_vec();
+    }
+
+    while bytes.len() > 1 && bytes.ends_with(b"/") {
+        bytes = &bytes[..bytes.len() - 1];
+    }
+
+    // Step 2: Check if it ends with `/.` and strip the `/+.` pattern
+    if bytes.ends_with(b".") && bytes.len() >= 2 {
+        let dot_pos = bytes.len() - 1;
+        if bytes[dot_pos - 1] == b'/' {
+            // Find where the slashes before the dot start
+            let mut slash_start = dot_pos - 1;
+            while slash_start > 0 && bytes[slash_start - 1] == b'/' {
+                slash_start -= 1;
+            }
+            // Return the stripped result
+            if slash_start == 0 {
+                // Result would be empty
+                return if path_bytes.starts_with(b"/") {
+                    b"/".to_vec()
+                } else {
+                    b".".to_vec()
+                };
             }
+            return bytes[..slash_start].to_vec();
         }
     }
+
+    // Step 3: Normal dirname - find last / and remove everything after it
+    if let Some(last_slash_pos) = bytes.iter().rposition(|&b| b == b'/') {
+        // Found a slash, remove everything after it
+        let mut result = &bytes[..last_slash_pos];
+
+        // Strip trailing slashes from result (but keep at least one if at the start)
+        while result.len() > 1 && result.ends_with(b"/") {
+            result = &result[..result.len() - 1];
+        }
+
+        if result.is_empty() {
+            return b"/".to_vec();
+        }
+
+        return result.to_vec();
+    }
+
+    // No slash found, return "."
+    b".".to_vec()
 }
 
 #[uucore::main]
@@ -83,27 +115,25 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 
     for path in &dirnames {
         let path_bytes = uucore::os_str_as_bytes(path.as_os_str()).unwrap_or(&[]);
+        let result = dirname_string_manipulation(path_bytes);
 
-        if handle_trailing_dot(path_bytes).is_none() {
-            // Normal path handling using Path::parent()
-            let p = Path::new(path);
-            match p.parent() {
-                Some(d) => {
-                    if d.components().next().is_none() {
-                        print!(".");
-                    } else {
-                        print_verbatim(d).unwrap();
-                    }
-                }
-                None => {
-                    if p.is_absolute() || path.as_os_str() == "/" {
-                        print!("/");
-                    } else {
-                        print!(".");
-                    }
-                }
+        #[cfg(unix)]
+        {
+            use std::os::unix::ffi::OsStrExt;
+            let result_os = std::ffi::OsStr::from_bytes(&result);
+            print_verbatim(result_os).unwrap();
+        }
+        #[cfg(not(unix))]
+        {
+            // On non-Unix, fall back to lossy conversion
+            if let Ok(s) = std::str::from_utf8(&result) {
+                print!("{s}");
+            } else {
+                // Fallback for non-UTF-8 paths on non-Unix systems
+                print!(".");
             }
         }
+
         print!("{line_ending}");
     }
 

tests/by-util/test_dirname.rs

@@ -9,6 +9,13 @@ fn test_invalid_arg() {
     new_ucmd!().arg("--definitely-invalid").fails_with_code(1);
 }
 
+#[test]
+fn test_missing_operand() {
+    // Test calling dirname with no arguments - should fail
+    // This covers the error path at line 80-82 in dirname.rs
+    new_ucmd!().fails_with_code(1);
+}
+
 #[test]
 fn test_path_with_trailing_slashes() {
     new_ucmd!()
@@ -156,7 +163,7 @@ fn test_trailing_dot_edge_cases() {
     new_ucmd!()
         .arg("/home/dos//.")
         .succeeds()
-        .stdout_is("/home/dos/\n");
+        .stdout_is("/home/dos\n");
 
     // Path with . in middle (should use normal logic)
     new_ucmd!()
@@ -216,3 +223,68 @@ fn test_existing_behavior_preserved() {
         .succeeds()
         .stdout_is("/home/dos\n");
 }
+
+#[test]
+fn test_multiple_paths_comprehensive() {
+    // Comprehensive test for multiple paths in single invocation
+    // Tests the loop at line 84 with various edge cases mixed
+    new_ucmd!()
+        .args(&[
+            "/home/dos/.",   // trailing dot case
+            "/var/log",      // normal path
+            ".",             // current directory
+            "/tmp/.",        // another trailing dot
+            "",              // empty string
+            "/",             // root
+            "relative/path", // relative path
+        ])
+        .succeeds()
+        .stdout_is("/home/dos\n/var\n.\n/tmp\n.\n/\nrelative\n");
+}
+
+#[test]
+fn test_all_dot_slash_variations() {
+    // Tests for all the cases mentioned in issue #8910 comment
+    // https://github.com/uutils/coreutils/issues/8910#issuecomment-3408735720
+
+    // foo//. -> foo
+    new_ucmd!().arg("foo//.").succeeds().stdout_is("foo\n");
+
+    // foo///. -> foo
+    new_ucmd!().arg("foo///.").succeeds().stdout_is("foo\n");
+
+    // foo/./ -> foo
+    new_ucmd!().arg("foo/./").succeeds().stdout_is("foo\n");
+
+    // foo/bar/./ -> foo/bar
+    new_ucmd!()
+        .arg("foo/bar/./")
+        .succeeds()
+        .stdout_is("foo/bar\n");
+
+    // foo/./bar -> foo/.
+    new_ucmd!().arg("foo/./bar").succeeds().stdout_is("foo/.\n");
+}
+
+#[test]
+fn test_dot_slash_component_preservation() {
+    // Ensure that /. components in the middle are preserved
+    // These should NOT be normalized away
+
+    new_ucmd!().arg("a/./b").succeeds().stdout_is("a/.\n");
+
+    new_ucmd!()
+        .arg("a/./b/./c")
+        .succeeds()
+        .stdout_is("a/./b/.\n");
+
+    new_ucmd!()
+        .arg("foo/./bar/baz")
+        .succeeds()
+        .stdout_is("foo/./bar\n");
+
+    new_ucmd!()
+        .arg("/path/./to/file")
+        .succeeds()
+        .stdout_is("/path/./to\n");
+}