realpath: Error when resolved symlink is absolute and ENOENT (#3037)

* realpath: Match behavior where resolving symlinks with absolute path is an error if ENOENT

This PR changes `realpath` to match the behavior in GNU where,

```shell
hbina@akarin ~/Documents> mkdir dir1
hbina@akarin ~/Documents> mkdir dir2
hbina@akarin ~/Documents> touch dir2/bar
hbina@akarin ~/Documents> ln -s ../dir2/bar dir1/foo1
hbina@akarin ~/Documents> ln -s /dir2/bar dir1/foo2
hbina@akarin ~/Documents> ln -s ../dir2/baz dir1/foo3
hbina@akarin ~/Documents> realpath ./dir1/foo1 ./dir1/foo2 ./dir1/foo3
/home/hbina/Documents/dir2/bar
realpath: ./dir1/foo2: No such file or directory
/home/hbina/Documents/dir2/baz
```

Currently, our `realpath` will happily print the second one out,

```shell
hbina@akarin ~/Documents> ~/git/uutils/target/debug/coreutils realpath ./dir1/foo1 ./dir1/foo2 ./dir1/foo3
/home/hbina/Documents/dir2/bar
/dir2/bar
/home/hbina/Documents/dir2/baz
```

Closes https://github.com/uutils/coreutils/issues/3036

Signed-off-by: Hanif Ariffin <hanif.ariffin.4326@gmail.com>

src/uucore/src/lib/features/fs.rs

@@ -223,15 +223,17 @@ pub fn normalize_path(path: &Path) -> PathBuf {
     ret
 }
 
-fn resolve<P: AsRef<Path>>(original: P) -> Result<PathBuf, (PathBuf, IOError)> {
+fn resolve<P: AsRef<Path>>(original: P) -> Result<PathBuf, (bool, PathBuf, IOError)> {
     const MAX_LINKS_FOLLOWED: u32 = 255;
     let mut followed = 0;
     let mut result = original.as_ref().to_path_buf();
-
+    let mut symlink_is_absolute = false;
     let mut first_resolution = None;
+
     loop {
         if followed == MAX_LINKS_FOLLOWED {
             return Err((
+                symlink_is_absolute,
                 // When we hit MAX_LINKS_FOLLOWED we should return the first resolution (that's what GNU does - for whatever reason)
                 first_resolution.unwrap(),
                 Error::new(ErrorKind::InvalidInput, "maximum links followed"),
@@ -244,16 +246,17 @@ fn resolve<P: AsRef<Path>>(original: P) -> Result<PathBuf, (PathBuf, IOError)> {
                     break;
                 }
             }
-            Err(e) => return Err((result, e)),
+            Err(e) => return Err((symlink_is_absolute, result, e)),
         }
 
         followed += 1;
         match fs::read_link(&result) {
             Ok(path) => {
                 result.pop();
+                symlink_is_absolute = path.is_absolute();
                 result.push(path);
             }
-            Err(e) => return Err((result, e)),
+            Err(e) => return Err((symlink_is_absolute, result, e)),
         }
 
         if first_resolution.is_none() {
@@ -343,8 +346,13 @@ pub fn canonicalize<P: AsRef<Path>>(
             }
 
             match resolve(&result) {
-                Err((path, _)) if miss_mode == MissingHandling::Missing => result = path,
+                Err((_, path, e)) => {
-                Err((_, e)) => return Err(e),
+                    if miss_mode == MissingHandling::Missing {
+                        result = path;
+                    } else {
+                        return Err(e);
+                    }
+                }
                 Ok(path) => {
                     result = path;
                 }
@@ -358,10 +366,20 @@ pub fn canonicalize<P: AsRef<Path>>(
         }
 
         match resolve(&result) {
-            Err((_, e)) if miss_mode == MissingHandling::Existing => {
+            Err((is_absolute, path, err)) => {
-                return Err(e);
+                // If the resolved symlink is an absolute path and non-existent,
+                // `realpath` throws no such file error.
+                if miss_mode == MissingHandling::Existing
+                    || (err.kind() == ErrorKind::NotFound
+                        && is_absolute
+                        && miss_mode == MissingHandling::Normal)
+                {
+                    return Err(err);
+                } else {
+                    result = path;
+                }
             }
-            Ok(path) | Err((path, _)) => {
+            Ok(path) => {
                 result = path;
             }
         }

tests/by-util/test_realpath.rs

@@ -149,8 +149,8 @@ fn test_realpath_dangling() {
     let (at, mut ucmd) = at_and_ucmd!();
     at.symlink_file("nonexistent-file", "link");
     ucmd.arg("link")
-        .succeeds()
+        .fails()
-        .stdout_only(at.plus_as_string("nonexistent-file\n"));
+        .stderr_contains("realpath: link: No such file or directory");
 }
 
 #[test]
@@ -202,3 +202,34 @@ fn test_realpath_missing() {
         .succeeds()
         .stdout_only(expect);
 }
+
+#[test]
+fn test_realpath_when_symlink_is_absolute_and_enoent() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.mkdir("dir2");
+    at.touch("dir2/bar");
+
+    at.mkdir("dir1");
+    at.symlink_file("dir2/bar", "dir1/foo1");
+    at.symlink_file("/dir2/bar", "dir1/foo2");
+    at.relative_symlink_file("dir2/baz", at.plus("dir1/foo3").to_str().unwrap());
+
+    #[cfg(unix)]
+    ucmd.arg("dir1/foo1")
+        .arg("dir1/foo2")
+        .arg("dir1/foo3")
+        .run()
+        .stdout_contains("/dir2/bar\n")
+        .stdout_contains("/dir2/baz\n")
+        .stderr_is("realpath: dir1/foo2: No such file or directory");
+
+    #[cfg(windows)]
+    ucmd.arg("dir1/foo1")
+        .arg("dir1/foo2")
+        .arg("dir1/foo3")
+        .run()
+        .stdout_contains("\\dir2\\bar\n")
+        .stdout_contains("\\dir2\\baz\n")
+        .stderr_is("realpath: dir1/foo2: No such file or directory");
+}

tests/common/util.rs

@@ -701,6 +701,11 @@ impl AtPath {
         symlink_file(&self.plus(original), &self.plus(link)).unwrap();
     }
 
+    pub fn relative_symlink_file(&self, original: &str, link: &str) {
+        log_info("symlink", &format!("{},{}", original, link));
+        symlink_file(original, link).unwrap();
+    }
+
     pub fn symlink_dir(&self, original: &str, link: &str) {
         log_info(
             "symlink",