The Oniguruma C engine permanently stores the syntax pointer inside re_pattern_buffer (via onig_reg_init), but the safe Rust API did not express this dependency — allowing a custom Syntax to be dropped while the Regex was still live, yielding a dangling pointer.

Approach

Add a 'syntax lifetime parameter to Regex backed by PhantomData<&'syntax Syntax>, surfacing the C-level memory dependency to the borrow checker at zero runtime cost.

Changes

• Regex<'syntax> — new lifetime parameter + _syntax: PhantomData<&'syntax Syntax> field; Send/Sync/Drop impls updated accordingly.
• Constructors:
  • new / with_encoding → explicitly return Regex<'static> (use Syntax::default() which is 'static; no new restriction on callers)
  • with_options<'s>(..., syntax: &'s Syntax) -> Result<Regex<'s>, Error> — returned Regex cannot outlive syntax
  • with_options_and_encoding<'s, T>(..., syntax: &'s Syntax) -> Result<Regex<'s>, Error> — same
• Iterator types — 'syntax added as an independent lifetime parameter (separate from the regex reference lifetime 'r):
  • FindMatches<'r, 'syntax, 't>, FindCaptures<'r, 'syntax, 't>, RegexSplits<'r, 'syntax, 't>, RegexSplitsN<'r, 'syntax, 't>
• pattern.rs — RegexSearcher<'r, 'syntax, 'a>; impl<'r, 'syntax> Pattern for &'r Regex<'syntax>

Example

// Before: compiled fine, but custom_syntax could be freed while regex was live
let regex = {
    let custom_syntax = *Syntax::default();
    Regex::with_options("hello", RegexOptions::REGEX_OPTION_NONE, &custom_syntax).unwrap()
    // custom_syntax dropped here — dangling pointer in the C engine
};

// After: compiler rejects this — `custom_syntax does not live long enough`

Callers using Regex::new or Regex::with_options(..., Syntax::default()) are unaffected — the returned type is Regex<'static>.