expand: avoid an infinite loop

src/uu/expand/src/expand.rs

@@ -11,11 +11,12 @@ use std::fmt;
 use std::fs::File;
 use std::io::{stdin, stdout, BufRead, BufReader, BufWriter, Read, Write};
 use std::num::IntErrorKind;
+use std::path::Path;
 use std::str::from_utf8;
 use unicode_width::UnicodeWidthChar;
 use uucore::display::Quotable;
-use uucore::error::{FromIo, UError, UResult};
-use uucore::{format_usage, help_about, help_usage};
+use uucore::error::{set_exit_code, FromIo, UError, UResult};
+use uucore::{format_usage, help_about, help_usage, show_error};
 
 const ABOUT: &str = help_about!("expand.md");
 const USAGE: &str = help_usage!("expand.md");
@@ -465,6 +466,12 @@ fn expand(options: &Options) -> UResult<()> {
     let mut buf = Vec::new();
 
     for file in &options.files {
+        if Path::new(file).is_dir() {
+            show_error!("{}: Is a directory", file);
+            set_exit_code(1);
+            continue;
+        }
+
         let mut fh = open(file)?;
 
         while match fh.read_until(b'\n', &mut buf) {

tests/by-util/test_expand.rs

@@ -409,3 +409,11 @@ int main() {
 ",
         );
 }
+
+#[test]
+fn test_expand_directory() {
+    new_ucmd!()
+        .args(&["."])
+        .fails()
+        .stderr_contains("expand: .: Is a directory");
+}