more: add error message if the argument is a directory (#1983)

src/uu/more/src/more.rs

@@ -41,7 +41,7 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
 
     let matches = App::new(executable!())
         .version(VERSION)
-        .usage(&usage[..])
+        .usage(usage.as_str())
         .about(ABOUT)
         .arg(
             Arg::with_name(options::FILE)
@@ -52,10 +52,18 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
 
     // FixME: fail without panic for now; but `more` should work with no arguments (ie, for piped input)
     if let None | Some("-") = matches.value_of(options::FILE) {
-        println!("{}: incorrect usage", executable!());
+        show_usage_error!("Reading from stdin isn't supported yet.");
         return 1;
     }
 
+    if let Some(x) = matches.value_of(options::FILE) {
+        let path = std::path::Path::new(x);
+        if path.is_dir() {
+            show_usage_error!("'{}' is a directory.", x);
+            return 1;
+        }
+    }
+
     more(matches);
 
     0

tests/by-util/test_more.rs

@@ -6,3 +6,14 @@ fn test_more_no_arg() {
     let result = ucmd.run();
     assert!(!result.success);
 }
+
+#[test]
+fn test_more_dir_arg() {
+    let (_, mut ucmd) = at_and_ucmd!();
+    ucmd.arg(".");
+    let result = ucmd.run();
+    assert!(!result.success);
+    const EXPECTED_ERROR_MESSAGE: &str =
+        "more: '.' is a directory.\nTry 'more --help' for more information.";
+    assert_eq!(result.stderr.trim(), EXPECTED_ERROR_MESSAGE);
+}