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tac: fix stdin piping on Windows by skipping empty mmap results #10795

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Merged
RenjiSann merged 1 commit into from
Feb 7, 2026
+5 −28
Merged

tac: fix stdin piping on Windows by skipping empty mmap results #10795

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6 changes: 5 additions & 1 deletion src/uu/tac/src/tac.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -411,7 +411,11 @@ fn tac(filenames: &[OsString], before: bool, regex: bool, separator: &str) -> UR
fn try_mmap_stdin() -> Option<Mmap> {
// SAFETY: If the file is truncated while we map it, SIGBUS will be raised
// and our process will be terminated, thus preventing access of invalid memory.
unsafe { Mmap::map(&stdin()).ok() }
let mmap = unsafe { Mmap::map(&stdin()).ok()? };
// On Windows, mmap on a pipe handle can "succeed" but return 0 bytes
// (the file size of a pipe is reported as 0). When that happens, return
// None so we fall through to buffer_stdin() which reads the pipe properly.
if mmap.is_empty() { None } else { Some(mmap) }
}

enum StdinData {
Expand Down
27 changes: 0 additions & 27 deletions tests/by-util/test_tac.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,8 +29,6 @@ fn test_invalid_arg() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_stdin_default() {
new_ucmd!()
.pipe_in("100\n200\n300\n400\n500")
Expand All @@ -39,8 +37,6 @@ fn test_stdin_default() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_stdin_non_newline_separator() {
new_ucmd!()
.args(&["-s", ":"])
Expand All @@ -50,8 +46,6 @@ fn test_stdin_non_newline_separator() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_stdin_non_newline_separator_before() {
new_ucmd!()
.args(&["-b", "-s", ":"])
Expand Down Expand Up @@ -104,14 +98,11 @@ fn test_invalid_input() {
}

#[test]
#[cfg(not(windows))] // FIXME: https://github.com/uutils/coreutils/issues/4204
fn test_no_line_separators() {
new_ucmd!().pipe_in("a").succeeds().stdout_is("a");
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_before_trailing_separator_no_leading_separator() {
new_ucmd!()
.arg("-b")
Expand All @@ -121,8 +112,6 @@ fn test_before_trailing_separator_no_leading_separator() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_before_trailing_separator_and_leading_separator() {
new_ucmd!()
.arg("-b")
Expand All @@ -132,8 +121,6 @@ fn test_before_trailing_separator_and_leading_separator() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_before_leading_separator_no_trailing_separator() {
new_ucmd!()
.arg("-b")
Expand All @@ -143,8 +130,6 @@ fn test_before_leading_separator_no_trailing_separator() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_before_no_separator() {
new_ucmd!()
.arg("-b")
Expand All @@ -154,15 +139,11 @@ fn test_before_no_separator() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_before_empty_file() {
new_ucmd!().arg("-b").pipe_in("").succeeds().stdout_is("");
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_multi_char_separator() {
new_ucmd!()
.args(&["-s", "xx"])
Expand Down Expand Up @@ -204,8 +185,6 @@ fn test_multi_char_separator_overlap() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_multi_char_separator_overlap_before() {
// With the "-b" option, the line separator is assumed to be at the
// beginning of the line. In this case, That is, "axxx" is
Expand Down Expand Up @@ -248,8 +227,6 @@ fn test_multi_char_separator_overlap_before() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_null_separator() {
new_ucmd!()
.args(&["-s", ""])
Expand All @@ -259,8 +236,6 @@ fn test_null_separator() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_regex() {
new_ucmd!()
.args(&["-r", "-s", "[xyz]+"])
Expand Down Expand Up @@ -289,8 +264,6 @@ fn test_regex() {
}

#[test]
// FIXME: See https://github.com/uutils/coreutils/issues/4204
#[cfg(not(windows))]
fn test_regex_before() {
new_ucmd!()
.args(&["-b", "-r", "-s", "[xyz]+"])
Expand Down
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