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date: width prefix in %N format specifier fix #12098

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date: width prefix in %N format specifier fix #12098

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6df88d3
Implement no_pad logic for 'N' specifier
blixygetir Apr 27, 2026
93ad040
Fix negative width prefix handling for %N format specifier
Apr 29, 2026
88f389b
my test
Apr 30, 2026
864853b
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Apr 30, 2026
86c66d7
fix-two
May 1, 2026
a6b25ac
fix three
May 1, 2026
b241b1c
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] May 1, 2026
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14 changes: 12 additions & 2 deletions src/uu/date/src/format_modifiers.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -75,8 +75,7 @@ struct ParsedSpec<'a> {
/// Flag characters from `[_0^#+-]`.
flags: &'a str,
/// Explicit width, if present. `None` means no width was specified.
/// A value that overflows `usize` is represented as `Some(usize::MAX)` so
/// the downstream allocation check surfaces it as `FieldWidthTooLarge`.
/// Width overflows are handled naturally by usize parsing.
width: Option<usize>,
/// The specifier itself, including any leading colons (e.g. `Y`, `:z`, `::z`).
spec: &'a str,
Expand Down Expand Up @@ -411,6 +410,16 @@ fn apply_modifiers(value: &str, parsed: &ParsedSpec<'_>) -> Result<String, Forma

// If no_pad flag is active, suppress all padding and return
if no_pad {
if specifier.ends_with('N') {
if let Some(w) = width {
// Truncate from the right by keeping the leftmost characters,
// using char iteration to avoid slicing at a non-UTF-8 boundary.
let truncated: String = result.chars().take(w).collect();
// Return truncated nanoseconds without trimming trailing zeros (GNU behavior)
return Ok(truncated);
}
Comment on lines 411 to +420
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Copilot AI Apr 30, 2026

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The new no_pad handling truncates result whenever a width is present, and returns early without strip_default_padding. This breaks existing documented/tested behavior that %-5d ignores width and still strips default padding (see tests in this module). Additionally, &result[..end] truncates from the left and can panic on non-ASCII output (not guaranteed to be on a UTF-8 char boundary). This truncation logic should be limited to the %N specifier (if required), should preserve existing no-pad behavior for other specifiers, and should implement the intended direction (right-truncation per PR description) safely.

Suggested change
// If no_pad flag is active, suppress all padding and return
if no_pad {
if let Some(w) = width {
let abs_w = w.abs() as usize;
let end = abs_w.min(result.len());
let truncated = &result[..end];
// Return truncated nanoseconds without trimming trailing zeros (GNU behavior)
return Ok(truncated.to_string());
}
// If no_pad flag is active, suppress all padding and return.
// Width-based truncation only applies to %N; other specifiers keep the
// documented behavior of ignoring width and stripping default padding.
if no_pad {
if specifier == "N" {
if let Some(w) = width {
let abs_w = w.abs() as usize;
// Truncate from the right by keeping the leftmost characters,
// using char iteration to avoid slicing at a non-UTF-8 boundary.
let truncated: String = result.chars().take(abs_w).collect();
// Return truncated nanoseconds without trimming trailing zeros (GNU behavior)
return Ok(truncated);
}
}

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}
// For all other specifiers (and %N without width), just strip padding
return Ok(strip_default_padding(&result));
}

Expand Down Expand Up @@ -988,6 +997,7 @@ mod tests {

for (input, expected) in cases {
let actual = parse_format_spec(input).map(|p| (p.flags, p.width, p.spec, p.len));

assert_eq!(actual, *expected, "input = {input:?}");
}
}
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