From 072331e88cab8e85c2ea2ec84e0f454ae32a97e2 Mon Sep 17 00:00:00 2001
From: xtqqczze <45661989+xtqqczze@users.noreply.github.com>
Date: Mon, 5 Oct 2026 15:56:14 +0100
Subject: [PATCH] Revert "tail: stop reading past the original end of file"

This reverts commit 781ddfc58cd5a283c5e53b3d5c8743d046afd366.
---
 src/uu/tail/src/tail.rs    | 13 ++-----------
 tests/by-util/test_tail.rs | 28 ----------------------------
 2 files changed, 2 insertions(+), 39 deletions(-)

diff --git a/src/uu/tail/src/tail.rs b/src/uu/tail/src/tail.rs
index 3c097f8f3..9db1ceadf 100644
--- a/src/uu/tail/src/tail.rs
+++ b/src/uu/tail/src/tail.rs
@@ -178,7 +178,7 @@ fn tail_file(
                     && file.is_seekable(if input.is_stdin() { offset } else { 0 })
                     && (!st.is_file() || st.len() > blksize_limit)
                 {
-                    bounded_tail(&mut file, settings, st.is_file().then_some(st.len()))?;
+                    bounded_tail(&mut file, settings)?;
                     reader = BufReader::new(file);
                 } else {
                     reader = BufReader::new(file);
@@ -452,7 +452,7 @@ fn backwards_thru_file(file: &mut File, num_delimiters: u64, delimiter: u8) {
 /// end of the file, and then read the file "backwards" in blocks of size
 /// `BLOCK_SIZE` until we find the location of the first line/byte. This ends up
 /// being a nice performance win for very large files.
-fn bounded_tail(file: &mut File, settings: &Settings, file_size: Option<u64>) -> UResult<()> {
+fn bounded_tail(file: &mut File, settings: &Settings) -> UResult<()> {
     debug_assert!(!settings.presume_input_pipe);
     let mut limit = None;
 
@@ -460,15 +460,6 @@ fn bounded_tail(file: &mut File, settings: &Settings, file_size: Option<u64>) ->
     match &settings.mode {
         FilterMode::Lines(Signum::Negative(count), delimiter) => {
             backwards_thru_file(file, *count, *delimiter);
-            // Print only up to the end the file had when it was opened.
-            // Otherwise, if the output is appended back to the input file
-            // (e.g. `tail -n1 f >> f`), reading until EOF never terminates
-            // because our own output keeps extending it.
-            if let Some(size) = file_size
-                && let Ok(pos) = file.stream_position()
-            {
-                limit = Some(size.saturating_sub(pos));
-            }
         }
         FilterMode::Lines(Signum::Positive(count), delimiter) if count > &1 => {
             let i = forwards_thru_file(file, *count - 1, *delimiter).unwrap();
diff --git a/tests/by-util/test_tail.rs b/tests/by-util/test_tail.rs
index 7c229fd35..9758f5cf7 100644
--- a/tests/by-util/test_tail.rs
+++ b/tests/by-util/test_tail.rs
@@ -263,34 +263,6 @@ fn test_n0_with_follow() {
     child.kill();
 }
 
-#[test]
-#[cfg(unix)]
-#[cfg_attr(wasi_runner, ignore = "WASI: no rlimit support")]
-fn test_output_appended_to_input_file_terminates() {
-    // $ tail -n1 f >> f
-    // Appends the last line once and exits; it must not read back its
-    // own output forever. The file size limit makes a broken
-    // implementation fail instead of filling the disk.
-    use rustix::process::Resource;
-
-    let (at, mut ucmd) = at_and_ucmd!();
-
-    // Larger than the filesystem block size so `tail` reads from the end.
-    let content = "x".repeat(256 * 1024) + "\n";
-    at.write("f", &content);
-    let out = std::fs::OpenOptions::new()
-        .append(true)
-        .open(at.plus("f"))
-        .unwrap();
-
-    ucmd.args(&["-n1", "f"])
-        .set_stdout(Stdio::from(out))
-        .limit(Resource::Fsize, 4 * 1024 * 1024, 4 * 1024 * 1024)
-        .succeeds();
-
-    assert_eq!(at.read("f"), content.repeat(2));
-}
-
 // TODO: Add similar test for windows
 #[test]
 #[cfg(unix)]