nl: support --join-blank-lines over multiple files

src/uu/nl/src/nl.rs

@@ -303,15 +303,14 @@ pub fn uu_app() -> Command {
 // nl implements the main functionality for an individual buffer.
 fn nl<T: Read>(reader: &mut BufReader<T>, stats: &mut Stats, settings: &Settings) -> UResult<()> {
     let mut current_numbering_style = &settings.body_numbering;
-    let mut consecutive_empty_lines = stats.consecutive_empty_lines;
 
     for line in reader.lines() {
         let line = line.map_err_context(|| "could not read line".to_string())?;
 
         if line.is_empty() {
-            consecutive_empty_lines += 1;
+            stats.consecutive_empty_lines += 1;
         } else {
-            consecutive_empty_lines = 0;
+            stats.consecutive_empty_lines = 0;
         };
 
         // FIXME section delimiters are hardcoded and settings.section_delimiter is ignored
@@ -336,7 +335,7 @@ fn nl<T: Read>(reader: &mut BufReader<T>, stats: &mut Stats, settings: &Settings
                 // for numbering, and only number the last one
                 NumberingStyle::All
                     if line.is_empty()
-                        && consecutive_empty_lines % settings.join_blank_lines != 0 =>
+                        && stats.consecutive_empty_lines % settings.join_blank_lines != 0 =>
                 {
                     false
                 }

tests/by-util/test_nl.rs

@@ -284,6 +284,31 @@ fn test_join_blank_lines() {
     }
 }
 
+#[test]
+fn test_join_blank_lines_multiple_files() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    at.write("a.txt", "\n\n");
+    at.write("b.txt", "\n\n");
+    at.write("c.txt", "\n\n");
+
+    for arg in ["-l3", "--join-blank-lines=3"] {
+        scene
+            .ucmd()
+            .args(&[arg, "--body-numbering=a", "a.txt", "b.txt", "c.txt"])
+            .succeeds()
+            .stdout_is(concat!(
+                "       \n",
+                "       \n",
+                "     1\t\n",
+                "       \n",
+                "       \n",
+                "     2\t\n",
+            ));
+    }
+}
+
 #[test]
 fn test_join_blank_lines_zero() {
     for arg in ["-l0", "--join-blank-lines=0"] {