From fdc2113ac0303dd50e901ad9435b3f1082f1e9e8 Mon Sep 17 00:00:00 2001
From: NAITOH Jun <naitoh@gmail.com>
Date: Mon, 8 Jan 2024 14:52:50 +0900
Subject: [PATCH] fix captures nil case

fix https://github.com/ruby/strscan/issues/70
---
 .../jruby/ext/strscan/RubyStringScanner.java   |  7 ++++++-
 ext/strscan/strscan.c                          | 18 +++++++++++-------
 test/strscan/test_stringscanner.rb             |  4 ++--
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java b/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
index 0b4d6338ff..89e7e09a05 100644
--- a/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
+++ b/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
@@ -901,9 +901,14 @@ public IRubyObject captures(ThreadContext context) {
         newAry = RubyArray.newArray(runtime, numRegs);
 
         for (i = 1; i < numRegs; i++) {
-            IRubyObject str = extractRange(runtime,
+            IRubyObject str;
+            if (REGION_ADAPTER.getBeg(regs, i) == -1) {
+                str = context.nil;
+            } else {
+                str = extractRange(runtime,
                     adjustRegisterPosition(REGION_ADAPTER.getBeg(regs, i)),
                     adjustRegisterPosition(REGION_ADAPTER.getEnd(regs, i)));
+            }
             newAry.push(str);
         }
 
diff --git a/ext/strscan/strscan.c b/ext/strscan/strscan.c
index a2bf56ce4f..7dbd971ae9 100644
--- a/ext/strscan/strscan.c
+++ b/ext/strscan/strscan.c
@@ -1243,10 +1243,10 @@ strscan_size(VALUE self)
  * If nothing was priorly matched, it returns nil.
  *
  *   s = StringScanner.new("Fri Dec 12 1975 14:39")
- *   s.scan(/(\w+) (\w+) (\d+) /)       # -> "Fri Dec 12 "
- *   s.captures                         # -> ["Fri", "Dec", "12"]
- *   s.scan(/(\w+) (\w+) (\d+) /)       # -> nil
- *   s.captures                         # -> nil
+ *   s.scan(/(\w+) (\w+) (\d+) (1980)?/)       # -> "Fri Dec 12 "
+ *   s.captures                                # -> ["Fri", "Dec", "12", nil]
+ *   s.scan(/(\w+) (\w+) (\d+) (1980)?/)       # -> nil
+ *   s.captures                                # -> nil
  */
 static VALUE
 strscan_captures(VALUE self)
@@ -1262,9 +1262,13 @@ strscan_captures(VALUE self)
     new_ary  = rb_ary_new2(num_regs);
 
     for (i = 1; i < num_regs; i++) {
-        VALUE str = extract_range(p,
-                                  adjust_register_position(p, p->regs.beg[i]),
-                                  adjust_register_position(p, p->regs.end[i]));
+        VALUE str;
+        if (p->regs.beg[i] == -1)
+            str = Qnil;
+        else
+            str = extract_range(p,
+                                adjust_register_position(p, p->regs.beg[i]),
+                                adjust_register_position(p, p->regs.end[i]));
         rb_ary_push(new_ary, str);
     }
 
diff --git a/test/strscan/test_stringscanner.rb b/test/strscan/test_stringscanner.rb
index 2fce4c3e74..29626b159f 100644
--- a/test/strscan/test_stringscanner.rb
+++ b/test/strscan/test_stringscanner.rb
@@ -737,8 +737,8 @@ def test_size
   def test_captures
     s = create_string_scanner("Timestamp: Fri Dec 12 1975 14:39")
     s.scan("Timestamp: ")
-    s.scan(/(\w+) (\w+) (\d+) /)
-    assert_equal(["Fri", "Dec", "12"], s.captures)
+    s.scan(/(\w+) (\w+) (\d+) (1980)?/)
+    assert_equal(["Fri", "Dec", "12", nil], s.captures)
     s.scan(/(\w+) (\w+) (\d+) /)
     assert_nil(s.captures)
   end