uutils/coreutils

date: strftime flags propagate into composite specifiers (%-D, %-F, …)

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#11657 opened on Apr 5, 2026

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U - datefuzzinggood first issue

Description

Summary

GNU date treats composite strftime specifiers (%D, %F, %T, %r, %R, %c, %x, %X) as atomic: flags like - apply to the whole expansion, not to inner sub-fields. uutils lets the - flag propagate into the inner %m, producing 6/15/24 instead of 06/15/24.

Found by a fuzz_date run.

Reproduction

$ LC_ALL=C TZ=UTC /usr/bin/date -d '2024-06-15' '+%-D'
06/15/24

$ LC_ALL=C TZ=UTC target/debug/coreutils date -d '2024-06-15' '+%-D'
6/15/24

Test

#[test]
fn test_date_strftime_flag_on_composite() {
    new_ucmd!()
        .env("LC_ALL", "C")
        .env("TZ", "UTC")
        .arg("-d")
        .arg("2024-06-15")
        .arg("+%-D")
        .succeeds()
        .stdout_is("06/15/24\n");
}

Contributor guide

Tech stack
rust
Domain
cli
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Ruststrftime format specificationcoreutils date source
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Investigate the handling of strftime flags in the date command's format string parsing. Focus on how composite specifiers like %D are processed and whether flags propagate into sub specifiers. Look at the cross platform strftime implementation or the date module's format parsing code, likely in src/uu/date/src/. The existing test in the issue can be used as a baseline.