From 1c584e9d801632f28b43da490656a8123b549f50 Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Sat, 10 Jul 2021 22:02:18 +0430
Subject: [PATCH] LibRegex: Correctly parse BRE bracket expressions

Commonly, bracket expressions are in fact, enclosed in brackets.
---
 Tests/LibRegex/RegexLibC.cpp                |  6 ++++++
 Userland/Libraries/LibRegex/RegexParser.cpp | 18 +++++++++++++-----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/Tests/LibRegex/RegexLibC.cpp b/Tests/LibRegex/RegexLibC.cpp
index e922e4525e..04794dbc08 100644
--- a/Tests/LibRegex/RegexLibC.cpp
+++ b/Tests/LibRegex/RegexLibC.cpp
@@ -1149,4 +1149,10 @@ TEST_CASE(bre_basic)
     EXPECT_EQ(regcomp(&regex, "15{1,2}", REG_NOSUB | REG_ICASE), REG_NOERR);
     EXPECT_EQ(regexec(&regex, "15{1,2}", 0, NULL, 0), REG_NOERR);
     regfree(&regex);
+
+    EXPECT_EQ(regcomp(&regex, "1[56]", REG_NOSUB | REG_ICASE), REG_NOERR);
+    EXPECT_EQ(regexec(&regex, "15", 0, NULL, 0), REG_NOERR);
+    EXPECT_EQ(regexec(&regex, "16", 0, NULL, 0), REG_NOERR);
+    EXPECT_EQ(regexec(&regex, "17", 0, NULL, 0), REG_NOMATCH);
+    regfree(&regex);
 }
diff --git a/Userland/Libraries/LibRegex/RegexParser.cpp b/Userland/Libraries/LibRegex/RegexParser.cpp
index d794721d94..814759de4e 100644
--- a/Userland/Libraries/LibRegex/RegexParser.cpp
+++ b/Userland/Libraries/LibRegex/RegexParser.cpp
@@ -481,12 +481,20 @@ bool PosixBasicParser::parse_one_char_or_collation_element(ByteCode& bytecode, s
 
     Vector<CompareTypeAndValuePair> values;
     size_t bracket_minimum_length = 0;
-    if (!AbstractPosixParser::parse_bracket_expression(values, bracket_minimum_length))
-        return false;
 
-    bytecode.insert_bytecode_compare_values(move(values));
-    match_length_minimum += bracket_minimum_length;
-    return !has_error();
+    if (match(TokenType::LeftBracket)) {
+        consume();
+        if (!AbstractPosixParser::parse_bracket_expression(values, bracket_minimum_length))
+            return false;
+
+        consume(TokenType::RightBracket, Error::MismatchingBracket);
+
+        bytecode.insert_bytecode_compare_values(move(values));
+        match_length_minimum += bracket_minimum_length;
+        return !has_error();
+    }
+
+    return set_error(Error::InvalidPattern);
 }
 
 // =============================