refactor(preg): report unmatched groups as null throughout

The shim carried two reporting modes for the preg_* $matches maps: PHP's
default (trailing unmatched groups dropped, interior ones ""), and the
PREG_UNMATCHED_AS_NULL form, picked by calling a *_unmatched_as_null()
variant. The regex crate hands out Option<Match>, which maps onto the
null form directly, and no caller distinguished a dropped group from a
null one -- preg_match() and preg_match_all2() already reported nulls
unconditionally. Keep only the null form; the shim API no longer mirrors
PHP's flag set, which is intended.

Preg::is_match_with_indexed_captures() modelled PHP's "unset" as a
truncated Vec<String>, and now returns Vec<Option<String>>. That is what
Composer actually does: Preg::isMatch() always sets
PREG_UNMATCHED_AS_NULL, and its callers test groups with `!== null`.

preg_match_all(), preg_match_all_set_order() and
preg_split_delim_capture() still hand back Vec<String> and keep the ""
form.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/crates/shirabe/src/installer/binary_installer.rs b/crates/shirabe/src/installer/binary_installer.rs
index d5ece82f..606e943f 100644
--- a/crates/shirabe/src/installer/binary_installer.rs
+++ b/crates/shirabe/src/installer/binary_installer.rs
@@ -328,10 +328,10 @@ impl BinaryInstaller {
             &bin_contents,
         ) {
             // carry over the existing shebang if present, otherwise add our own
-            let proxy_code = if m.get(1).is_none() {
+            let proxy_code = if m[1].is_none() {
                 "#!/usr/bin/env php".to_string()
             } else {
-                trim(m.get(1).map(|s| s.as_str()).unwrap_or(""), None)
+                trim(m[1].as_deref().unwrap_or(""), None)
             };
             let bin_path_exported = self
                 .filesystem
@@ -377,7 +377,7 @@ impl BinaryInstaller {
                 $data = str_replace('__FILE__', var_export($this->realpath, true), $data);"
                     .to_string();
             }
-            if trim(m.first().map(|s| s.as_str()).unwrap_or(""), None) != "<?php" {
+            if trim(m[0].as_deref().unwrap_or(""), None) != "<?php" {
                 stream_hint =
                     " using a stream wrapper to prevent the shebang from being output on PHP<8\n *"
                         .to_string();