tr: document what a SET may hold in the help

[Ascol57]

Fixes #14688

tr --help, and so the generated man page, listed the options and stopped
there. The synopsis mentions [sets] and nothing said what a SET may hold, so
there was no way to learn about ranges, repeats, escapes or character classes
from the page. It came to 18 lines against GNU's 54.

The reporter hit this after upgrading to Ubuntu 26.04, which ships uutils.

What is documented

The text is written from what src/uu/tr/src/operation.rs actually parses,
not translated from GNU's wording, since the licenses are not compatible.
Every claim was checked against the binary and against GNU 9.7:

• the escapes \NNN (one to three octal digits), \\, \a, \b, \f,
  \n, \r, \t, \v
• ranges CHAR1-CHAR2
• [CHAR*] and [CHAR*REPEAT], with REPEAT read as octal when it starts
  with 0
• equivalence classes [=CHAR=]
• all twelve character classes the parser accepts, each described from the
  byte set it expands to — [:graph:] excludes the space and [:print:]
  includes it, [:blank:] is tab and space while [:space:] adds the
  vertical whitespace
• when translation happens, how SET2 is padded with its last character and
  how --truncate-set1 shortens SET1 instead, that only [:lower:] and
  [:upper:] may appear in SET2, and that squeezing applies to the last SET
  after any translation or deletion

The sets operand also gets a help string, so it no longer shows as a bare
[sets]... with an empty description.

French

fr-FR.ftl was at full parity with en-US.ftl before this change, so it is
translated too rather than left to fall back to English.

Checks

• moz-fluent-lint --config .github/fluent_linter_config.yml src/uu/tr/locales/
  reports no errors on both files.
• The generated man page renders cleanly: uudoc manpage tr | groff -man -ww
  emits no warnings, and the escapes come out as \NNN, \\, \a rather
  than doubled. Entries were kept short enough not to wrap, matching how the
  stat after-help block renders.
• The new test asserts the help documents the ranges, repeats, equivalence
  classes, escapes, every one of the twelve class names, and the operand
  description. Restoring the old one-line after-help makes it fail with
  the help does not document CHAR1-CHAR2.
• 162 tr tests pass, 169 with feat_diagnostics. clippy and cargo fmt
  clean.

[Copilot]

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Copilot review overview

Review effort: Lite
Findings: 2

Open (2)

• This sentence is grammatically incomplete because the subject of commence is omitted. Use wording… · New
• The adjective must agree with the masculine noun espaces; use espaces horizontaux. The same… · New

What changed in this PR

Documents the syntax and behavior of tr SET operands in help output and adds coverage to ensure the generated help remains informative.

Changes:

• Adds comprehensive English and French documentation for escapes, ranges, repeats, equivalence classes, character classes, and translation behavior.
• Adds a localized help description for the sets operand.
• Adds a regression test covering the documented SET syntax and operand description.

File	Description
tests/​by-util/​test_tr.rs	Verifies that help output documents SET syntax and all supported character classes.
src/​uu/​tr/​src/​tr.rs	Associates the localized SET description with the positional operand.
src/​uu/​tr/​locales/​fr-FR.ftl	Adds the French SET syntax and behavior documentation.
src/​uu/​tr/​locales/​en-US.ftl	Adds the English SET syntax and behavior documentation.

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[Copilot]

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Copilot couldn't run its full agentic review because it didn't start before the timeout. Make sure your repository has a runner available, or add a copilot-code-review.yml file specifying one with the runs-on attribute. See the docs for more details.

Copilot review overview

Review effort: Lite
Findings: 2

Open (2)

• The adjective must agree with the masculine noun espaces; use espaces horizontaux. The same…
• This sentence is grammatically incomplete because the subject of commence is omitted. Use wording…

[codspeed]

Merging this PR will degrade performance by 6.15%

❌ 1 regressed benchmark
✅ 7 untouched benchmarks
⏩ 424 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	tr_ascii_range_lower_to_upper	124.7 KB	132.9 KB	-6.15%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing Ascol57:tr-document-sets-in-help (f060119) with main (406e5a8)}

Footnotes

1. 424 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[Copilot]

Copilot review overview

🔵 Needs a closer look

Address the incomplete escape and equivalence-class documentation, and pin LC_ALL in the locale-sensitive test.

Review effort: Lite
Findings: None

Resolved since last review (2)

• The adjective must agree with the masculine noun espaces; use espaces horizontaux. The same…
• This sentence is grammatically incomplete because the subject of commence is omitted. Use wording…

[Ascol57]

I work on it when I come back from school.

[sylvestre]

clippy is sad on 5 jobs :)

error: empty line after outer attribute
    --> tests/by-util/test_tr.rs:1655:1
     |
1655 | / #[cfg(all(feature = "feat_diagnostics", not(wasi_runner)))]
1656 | |
     | |_^
1657 |   mod diagnostics {
     |   --------------- the attribute applies to this module
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.98.0/index.html#empty_line_after_outer_attr
     = note: `-D clippy::empty-line-after-outer-attr` implied by `-D warnings`
     = help: to override `-D warnings` add `#[allow(clippy::empty_line_after_outer_attr)]`
     = help: if the empty line is unintentional, remove it