From abc40bf770e2bff2ea1d3867b8853c1f8ee5c1d7 Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Mon, 27 Jan 2025 16:07:23 -0500
Subject: [PATCH] Return an error if a POSIX charclass is specified outside of
 brackets

---
 compile.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/compile.go b/compile.go
index 91b098c..93dc54d 100644
--- a/compile.go
+++ b/compile.go
@@ -481,6 +481,16 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 			if i >= len(re_postfix) {
 				return nil, fmt.Errorf("Opening bracket with no closing bracket.")
 			}
+
+			// Check if a POSIX character class was specified ouside a bracket. This is an error.
+			// Eg. [:digit:] should lead to an error, telling the user that the right syntax is [[:digit:]]
+			if re_postfix[i] == ':' {
+				posixClassPresent, _ := getPOSIXClass(re_postfix[i+1:])
+				if posixClassPresent {
+					return nil, fmt.Errorf("The syntax for POSIX character classes is [[:digit:]], not [:digit:]")
+				}
+			}
+
 			var invertMatch bool
 			if re_postfix[i] == '^' {
 				invertMatch = true