From ca95edb122481479ca20227359816f8ccab74304 Mon Sep 17 00:00:00 2001
From: ksss <co000ri@gmail.com>
Date: Tue, 9 Jun 2026 16:16:10 +0900
Subject: [PATCH] `MatchData#[]` support `%a{implicitly-returns-nil}`

In the following case, even though the return value of `Regexp.last_match`
cannot possibly be `nil`, the type still retains the possibility of being `nil`.

```rb
when /\AArray<(?<inner_type>.+)>\z/
  inner_type = Regexp.last_match[:inner_type]
```

Just like `Array#[]` and others, it would be more practical to make the possibility of `nil` implicit.
---
 core/match_data.rbs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/match_data.rbs b/core/match_data.rbs
index c64d9b6cf..09b06dd6b 100644
--- a/core/match_data.rbs
+++ b/core/match_data.rbs
@@ -92,7 +92,7 @@ class MatchData
   #     #<MatchData "hoge" foo:nil foo:"oge" foo:nil>
   #     m[:foo] #=> "oge"
   #
-  def []: (capture backref, ?nil) -> String?
+  def []: %a{implicitly-returns-nil} (capture backref, ?nil) -> String
         | (int start, int length) -> Array[String?]
         | (range[int?] range) -> Array[String?]