Tail macos stdin ran from script fix (#7844)

* fixes #7763

- introduce macOS-specific config guard
- added test for testing tail stdin when redirected (`>`) from file and
  when through a pipe (`|`)

* created test to mock behavior in #7763, with comments

added drop line

* re-enabled test_stdin_redirect_dir_when_target_os_is_macos, and added a check to handle error message

* added location of current directory so test env can find script

* adjusting to try to have FreeBSD find the file in CI test

* putting in /env instead of assuming bash

* removed ignore macro

* added comments explaining the need for specific macOS cases, including reference to rust-lang issue: rust-lang/rust#95239

Author: hz2

src/uu/tail/src/paths.rs

@@ -78,14 +78,18 @@ impl Input {
                 path.canonicalize().ok()
             }
             InputKind::File(_) | InputKind::Stdin => {
-                if cfg!(unix) {
-                    match PathBuf::from(text::DEV_STDIN).canonicalize().ok() {
-                        Some(path) if path != PathBuf::from(text::FD0) => Some(path),
-                        Some(_) | None => None,
-                    }
-                } else {
+                // on macOS, /dev/fd isn't backed by /proc and canonicalize()
+                // on dev/fd/0 (or /dev/stdin) will fail (NotFound),
+                // so we treat stdin as a pipe here
+                // https://github.com/rust-lang/rust/issues/95239
+                #[cfg(target_os = "macos")]
+                {
                     None
                 }
+                #[cfg(not(target_os = "macos"))]
+                {
+                    PathBuf::from(text::FD0).canonicalize().ok()
+                }
             }
         }
     }

src/uu/tail/src/tail.rs

@@ -189,6 +189,29 @@ fn tail_stdin(
     input: &Input,
     observer: &mut Observer,
 ) -> UResult<()> {
+    // on macOS, resolve() will always return None for stdin,
+    // we need to detect if stdin is a directory ourselves.
+    // fstat-ing certain descriptors under /dev/fd fails with
+    // bad file descriptor or might not catch directory cases
+    // e.g. see the differences between running ls -l /dev/stdin /dev/fd/0
+    // on macOS and Linux.
+    #[cfg(target_os = "macos")]
+    {
+        if let Ok(mut stdin_handle) = Handle::stdin() {
+            if let Ok(meta) = stdin_handle.as_file_mut().metadata() {
+                if meta.file_type().is_dir() {
+                    set_exit_code(1);
+                    show_error!(
+                        "cannot open '{}' for reading: {}",
+                        input.display_name,
+                        text::NO_SUCH_FILE
+                    );
+                    return Ok(());
+                }
+            }
+        }
+    }
+
     match input.resolve() {
         // fifo
         Some(path) => {

tests/by-util/test_tail.rs

@@ -346,6 +346,55 @@ fn test_stdin_redirect_dir_when_target_os_is_macos() {
         .stderr_is("tail: cannot open 'standard input' for reading: No such file or directory\n");
 }
 
+#[test]
+#[cfg(unix)]
+fn test_stdin_via_script_redirection_and_pipe() {
+    // $ touch file.txt
+    // $ echo line1 > file.txt
+    // $ echo line2 >> file.txt
+    // $ chmod +x test.sh
+    // $ ./test.sh < file.txt
+    // line1
+    // line2
+    // $ cat file.txt | ./test.sh
+    // line1
+    // line2
+    use std::os::unix::fs::PermissionsExt;
+
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+    let data = "line1\nline2\n";
+
+    at.write("file.txt", data);
+
+    let mut script = at.make_file("test.sh");
+    writeln!(script, "#!/usr/bin/env sh").unwrap();
+    writeln!(script, "tail").unwrap();
+    script
+        .set_permissions(PermissionsExt::from_mode(0o755))
+        .unwrap();
+
+    drop(script); // close the file handle to ensure file is not busy
+
+    // test with redirection
+    scene
+        .cmd("sh")
+        .current_dir(at.plus(""))
+        .arg("-c")
+        .arg("./test.sh < file.txt")
+        .succeeds()
+        .stdout_only(data);
+
+    // test with pipe
+    scene
+        .cmd("sh")
+        .current_dir(at.plus(""))
+        .arg("-c")
+        .arg("cat file.txt | ./test.sh")
+        .succeeds()
+        .stdout_only(data);
+}
+
 #[test]
 fn test_follow_stdin_descriptor() {
     let ts = TestScenario::new(util_name!());