From 00326a63ed6b07acfe437ccae1253b593463c75b Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Wed, 9 Nov 2022 21:34:36 +0330
Subject: [PATCH] LibRegex: Don't treat ForkReplace* as new forks

---
 Tests/LibRegex/Regex.cpp                      |  6 ++++++
 Userland/Libraries/LibRegex/RegexByteCode.cpp | 13 +++++++++----
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/Tests/LibRegex/Regex.cpp b/Tests/LibRegex/Regex.cpp
index abcfa93513..15e972a24d 100644
--- a/Tests/LibRegex/Regex.cpp
+++ b/Tests/LibRegex/Regex.cpp
@@ -1067,6 +1067,12 @@ TEST_CASE(negative_lookahead)
         EXPECT_EQ(re.match(":1"sv).success, false);
         EXPECT_EQ(re.match(":foobar"sv).success, true);
     }
+    {
+        // Correctly count forks with nested groups and optimised loops
+        Regex<ECMA262> re("^((?:[^\\n]|\\n(?! *\\n))+)(?:\\n *)+\\n");
+        EXPECT_EQ(re.match("foo\n\n"sv).success, true);
+        EXPECT_EQ(re.match("foo\n"sv).success, false);
+    }
 }
 
 TEST_CASE(single_match_flag)
diff --git a/Userland/Libraries/LibRegex/RegexByteCode.cpp b/Userland/Libraries/LibRegex/RegexByteCode.cpp
index e0c0ca4a27..e94ec356da 100644
--- a/Userland/Libraries/LibRegex/RegexByteCode.cpp
+++ b/Userland/Libraries/LibRegex/RegexByteCode.cpp
@@ -267,7 +267,6 @@ ALWAYS_INLINE ExecutionResult OpCode_ForkReplaceStay::execute(MatchInput const&
 {
     state.fork_at_position = state.instruction_position + size() + offset();
     input.fork_to_replace = state.instruction_position;
-    state.forks_since_last_save++;
     return ExecutionResult::Fork_PrioLow;
 }
 
@@ -384,8 +383,10 @@ ALWAYS_INLINE ExecutionResult OpCode_SaveRightCaptureGroup::execute(MatchInput c
 {
     auto& match = state.capture_group_matches.at(input.match_index).at(id());
     auto start_position = match.left_column;
-    if (state.string_position < start_position)
+    if (state.string_position < start_position) {
+        dbgln("Right capture group {} is before left capture group {}!", state.string_position, start_position);
         return ExecutionResult::Failed_ExecuteLowPrioForks;
+    }
 
     auto length = state.string_position - start_position;
 
@@ -1071,11 +1072,15 @@ ALWAYS_INLINE ExecutionResult OpCode_JumpNonEmpty::execute(MatchInput const& inp
 
         state.fork_at_position = state.instruction_position + size() + offset();
 
-        if (form == OpCodeId::ForkJump)
+        if (form == OpCodeId::ForkJump) {
+            state.forks_since_last_save++;
             return ExecutionResult::Fork_PrioHigh;
+        }
 
-        if (form == OpCodeId::ForkStay)
+        if (form == OpCodeId::ForkStay) {
+            state.forks_since_last_save++;
             return ExecutionResult::Fork_PrioLow;
+        }
 
         if (form == OpCodeId::ForkReplaceStay) {
             input.fork_to_replace = state.instruction_position;