expr: switch to leftmost-longest regex matching behavior

[keith-hall]

Fixes a bug in expr whereby it was using leftmost-first match semantics instead of leftmost-longest as required by POSIX

[Copilot]

🟢 Approval recommended

No unresolved review issues remain, and all reviewed changes are covered.

Pull request overview

Updates expr to use POSIX leftmost-longest regex matching.

Changes:

• Enables fancy-regex leftmost-longest matching.
• Adds an alternation regression test.
• Updates dependency metadata and lockfile.

File summaries

File	Description
src/uu/expr/src/syntax_tree.rs	Configures matching behavior and adds a regression test.
Cargo.toml	Updates and configures fancy-regex.
Cargo.lock	Records dependency metadata changes.

Review details

• Files reviewed: 2/3 changed files
• Comments generated: 0
• Review effort level: Lite

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[keith-hall]

Thankyou for adding unit test. But we prefer testing by actual expr binary at https://github.com/uutils/coreutils/blob/main/tests/by-util/test_expr.rs .

thanks, added a test here too

[Copilot]

🟢 Approval recommended

No unresolved review issues were identified.

Review details

• Files reviewed: 3/4 changed files
• Comments generated: 0 new
• Review effort level: Lite

[sylvestre]

please also update Cargo.lock in fuzz/

[keith-hall]

please also update Cargo.lock in fuzz/

done, thanks

[Copilot]

🟢 Approval recommended

No unresolved issues were identified.

Review details

• Files reviewed: 3/5 changed files
• Comments generated: 0 new
• Review effort level: Lite

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/cut/bounded-memory is now being skipped but was previously passing.

[sylvestre]

cool stuff, thanks

[oech3]

@keith-hall Should we use .seek(true) at expr too?

[keith-hall]

I would suggest to benchmark it and decide - if a match would be found at the beginning of the haystack, seeking might add unnecessary extra overhead... If the pattern is unanchored and the haystack is large, then likely it would make sense to seek.