tr: generate an error for real if the input is a directory

src/uu/tr/Cargo.toml

@@ -19,7 +19,7 @@ path = "src/tr.rs"
 [dependencies]
 nom = { workspace = true }
 clap = { workspace = true }
-uucore = { workspace = true }
+uucore = { workspace = true, features = ["fs"] }
 
 [[bin]]
 name = "tr"

src/uu/tr/src/tr.rs

@@ -8,17 +8,17 @@
 mod operation;
 mod unicode_table;
 
+use crate::operation::DeleteOperation;
 use clap::{crate_version, value_parser, Arg, ArgAction, Command};
 use operation::{
     translate_input, Sequence, SqueezeOperation, SymbolTranslator, TranslateOperation,
 };
 use std::ffi::OsString;
 use std::io::{stdin, stdout, BufWriter};
-use uucore::{format_usage, help_about, help_section, help_usage, os_str_as_bytes, show};
-
-use crate::operation::DeleteOperation;
 use uucore::display::Quotable;
 use uucore::error::{UResult, USimpleError, UUsageError};
+use uucore::fs::is_stdin_directory;
+use uucore::{format_usage, help_about, help_section, help_usage, os_str_as_bytes, show};
 
 const ABOUT: &str = help_about!("tr.md");
 const AFTER_HELP: &str = help_section!("after help", "tr.md");
@@ -126,6 +126,13 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         translating,
     )?;
 
+    if is_stdin_directory(&stdin) {
+        return Err(USimpleError::new(
+            1,
+            format!("{}: read error: Is a directory", uucore::util_name()),
+        ));
+    }
+
     // '*_op' are the operations that need to be applied, in order.
     if delete_flag {
         if squeeze_flag {

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

@@ -20,6 +20,7 @@ use std::ffi::{OsStr, OsString};
 use std::fs;
 use std::fs::read_dir;
 use std::hash::Hash;
+use std::io::Stdin;
 use std::io::{Error, ErrorKind, Result as IOResult};
 #[cfg(unix)]
 use std::os::unix::{fs::MetadataExt, io::AsRawFd};
@@ -721,6 +722,34 @@ pub fn path_ends_with_terminator(path: &Path) -> bool {
         .map_or(false, |wide| wide == b'/'.into() || wide == b'\\'.into())
 }
 
+/// Checks if the standard input (stdin) is a directory.
+///
+/// # Arguments
+///
+/// * `stdin` - A reference to the standard input handle.
+///
+/// # Returns
+///
+/// * `bool` - Returns `true` if stdin is a directory, `false` otherwise.
+pub fn is_stdin_directory(stdin: &Stdin) -> bool {
+    #[cfg(unix)]
+    {
+        use nix::sys::stat::fstat;
+        let mode = fstat(stdin.as_raw_fd()).unwrap().st_mode as mode_t;
+        has!(mode, S_IFDIR)
+    }
+
+    #[cfg(windows)]
+    {
+        use std::os::windows::io::AsRawHandle;
+        let handle = stdin.as_raw_handle();
+        if let Ok(metadata) = fs::metadata(format!("{}", handle as usize)) {
+            return metadata.is_dir();
+        }
+        false
+    }
+}
+
 pub mod sane_blksize {
 
     #[cfg(not(target_os = "windows"))]

tests/by-util/test_tr.rs

@@ -20,6 +20,14 @@ fn test_invalid_input() {
         .fails()
         .code_is(1)
         .stderr_contains("tr: extra operand '<'");
+    #[cfg(unix)]
+    new_ucmd!()
+        .args(&["1", "1"])
+        // will test "tr 1 1 < ."
+        .set_stdin(std::process::Stdio::from(std::fs::File::open(".").unwrap()))
+        .fails()
+        .code_is(1)
+        .stderr_contains("tr: read error: Is a directory");
 }
 
 #[test]