join: print unsorted line in error message

This expands the error message that is printed if either input file has
an unsorted line. Both the program name (join) and the offending line
are printed out with the message to match the behaviour of the GNU
utility.

src/uu/join/src/join.rs

@@ -235,6 +235,7 @@ impl Spec {
 
 struct Line {
     fields: Vec<Vec<u8>>,
+    string: Vec<u8>,
 }
 
 impl Line {
@@ -247,10 +248,10 @@ impl Line {
                 .map(Vec::from)
                 .collect(),
             Sep::Char(sep) => string.split(|c| *c == sep).map(Vec::from).collect(),
-            Sep::Line => vec![string],
+            Sep::Line => vec![string.clone()],
         };
 
-        Line { fields }
+        Line { fields, string }
     }
 
     /// Get field at index.
@@ -444,9 +445,11 @@ impl<'a> State<'a> {
 
         if diff == Ordering::Greater {
             eprintln!(
-                "{}:{}: is not sorted",
+                "{}: {}:{}: is not sorted: {}",
+                uucore::execution_phrase(),
                 self.file_name.maybe_quote(),
-                self.line_num
+                self.line_num,
+                String::from_utf8_lossy(&line.string)
             );
 
             // This is fatal if the check is enabled.

tests/by-util/test_join.rs

@@ -283,11 +283,16 @@ fn missing_format_fields() {
 
 #[test]
 fn wrong_line_order() {
+    let ts = TestScenario::new(util_name!());
     new_ucmd!()
         .arg("fields_2.txt")
         .arg("fields_4.txt")
         .fails()
-        .stderr_is("fields_4.txt:5: is not sorted");
+        .stderr_is(&format!(
+            "{} {}: fields_4.txt:5: is not sorted: 11 g 5 gh",
+            ts.bin_path.to_string_lossy(),
+            ts.util_name
+        ));
 }
 
 #[test]