From 878e3a0751e795f0d7cab5ab41e84844e7406bd1 Mon Sep 17 00:00:00 2001
From: hmelder <service@hugomelder.com>
Date: Mon, 28 Oct 2024 13:18:39 +0100
Subject: [PATCH] NSString: fix -commonPrefixWithString:options: behaviour

---
 Source/NSString.m           | 5 +++++
 Tests/base/NSString/basic.m | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/Source/NSString.m b/Source/NSString.m
index b0c85b4af9..8c7a296932 100644
--- a/Source/NSString.m
+++ b/Source/NSString.m
@@ -3227,6 +3227,11 @@ - (NSUInteger) hash
 - (NSString*) commonPrefixWithString: (NSString*)aString
 			     options: (NSUInteger)mask
 {
+  // Return empty string to match behaviour on macOS
+  if (nil == aString)
+    {
+      return @"";
+    }
   if (mask & NSLiteralSearch)
     {
       int prefix_len = 0;
diff --git a/Tests/base/NSString/basic.m b/Tests/base/NSString/basic.m
index d94b539c0b..2b87f05d2f 100644
--- a/Tests/base/NSString/basic.m
+++ b/Tests/base/NSString/basic.m
@@ -144,6 +144,9 @@ int main()
   PASS([@"" isEqual: nil] == NO, "an empty string is not null");
   PASS([@"" isEqualToString: nil] == NO, "an empty string is not null");
 
+  s = [@"test" commonPrefixWithString: nil options: 0];
+  PASS_EQUAL(s, @"", "Common prefix of some string with nil is empty string");
+
   [arp release]; arp = nil;
   return 0;
 }