tail: Reactivate ---presume-input-pipe option

src/uu/tail/src/tail.rs

@@ -159,7 +159,8 @@ fn tail_file(
             Ok(mut file) => {
                 input_service.print_header(input);
                 let mut reader;
-                if file.is_seekable(if input.is_stdin() { offset } else { 0 })
+                if !settings.presume_input_pipe
+                    && file.is_seekable(if input.is_stdin() { offset } else { 0 })
                     && metadata.as_ref().unwrap().get_block_size() > 0
                 {
                     bounded_tail(&mut file, settings);
@@ -379,9 +380,9 @@ fn backwards_thru_file(file: &mut File, num_delimiters: u64, delimiter: u8) {
 /// `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) {
+    debug_assert!(!settings.presume_input_pipe);
+
     // Find the position in the file to start printing from.
-    // dbg!("bounded");
-    // dbg!(&settings.mode);
     match &settings.mode {
         FilterMode::Lines(Signum::Negative(count), delimiter) => {
             backwards_thru_file(file, *count, *delimiter);
@@ -418,8 +419,6 @@ fn bounded_tail(file: &mut File, settings: &Settings) {
 fn unbounded_tail<T: Read>(reader: &mut BufReader<T>, settings: &Settings) -> UResult<()> {
     let stdout = stdout();
     let mut writer = BufWriter::new(stdout.lock());
-    // dbg!("unbounded");
-    // dbg!(&settings.mode);
     match &settings.mode {
         FilterMode::Lines(Signum::Negative(count), sep) => {
             let mut chunks = chunks::LinesChunkBuffer::new(*sep, *count);

tests/by-util/test_tail.rs

@@ -7,10 +7,9 @@
 // spell-checker:ignore (libs) kqueue
 // spell-checker:ignore (jargon) tailable untailable
 
-// TODO: add tests for presume_input_pipe
-
 extern crate tail;
 
+use crate::common::random::*;
 use crate::common::util::*;
 use std::char::from_digit;
 #[cfg(unix)]
@@ -2516,7 +2515,6 @@ fn test_illegal_seek() {
 #[cfg(all(not(target_os = "android"), not(target_os = "windows")))] // FIXME: See https://github.com/uutils/coreutils/issues/3881
 mod pipe_tests {
     use super::*;
-    use crate::common::random::*;
     use rand::distributions::Alphanumeric;
     use tail::chunks::BUFFER_SIZE as CHUNK_BUFFER_SIZE;
 
@@ -3251,3 +3249,75 @@ fn test_seek_bytes_forward_outside_file() {
         .run()
         .stdout_is("");
 }
+
+// Some basic tests for ---presume-input-pipe. These tests build upon the
+// debug_assert in bounded tail to detect that we're using the bounded_tail in
+// case the option is given on command line.
+#[cfg(all(not(target_os = "android"), not(target_os = "windows")))] // FIXME:
+#[test]
+fn test_args_when_presume_input_pipe_given_input_is_pipe() {
+    let random_string = RandomString::generate(AlphanumericNewline, 1000);
+    let random_string = random_string.as_str();
+
+    new_ucmd!()
+        .args(&["---presume-input-pipe", "-c", "-0"])
+        .pipe_in(random_string)
+        .ignore_stdin_write_error()
+        .succeeds()
+        .no_stdout()
+        .no_stderr();
+
+    new_ucmd!()
+        .args(&["---presume-input-pipe", "-c", "+0"])
+        .pipe_in(random_string)
+        .ignore_stdin_write_error()
+        .succeeds()
+        .stdout_only(random_string);
+
+    new_ucmd!()
+        .args(&["---presume-input-pipe", "-n", "-0"])
+        .pipe_in(random_string)
+        .ignore_stdin_write_error()
+        .succeeds()
+        .no_stdout()
+        .no_stderr();
+
+    new_ucmd!()
+        .args(&["---presume-input-pipe", "-n", "+0"])
+        .pipe_in(random_string)
+        .ignore_stdin_write_error()
+        .succeeds()
+        .stdout_only(random_string);
+}
+
+#[test]
+fn test_args_when_presume_input_pipe_given_input_is_file() {
+    let random_string = RandomString::generate(AlphanumericNewline, 1000);
+    let random_string = random_string.as_str();
+
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+    at.write("data", random_string);
+
+    ts.ucmd()
+        .args(&["---presume-input-pipe", "-c", "-0", "data"])
+        .succeeds()
+        .no_stdout()
+        .no_stderr();
+
+    ts.ucmd()
+        .args(&["---presume-input-pipe", "-c", "+0", "data"])
+        .succeeds()
+        .stdout_only(random_string);
+
+    ts.ucmd()
+        .args(&["---presume-input-pipe", "-n", "-0", "data"])
+        .succeeds()
+        .no_stdout()
+        .no_stderr();
+
+    ts.ucmd()
+        .args(&["---presume-input-pipe", "-n", "+0", "data"])
+        .succeeds()
+        .stdout_only(random_string);
+}