From e85dbf37be64e22e2c1f3786539f2e6831085147 Mon Sep 17 00:00:00 2001
From: Vinayak Mishra <viks@vnykmshr.com>
Date: Tue, 17 Feb 2026 11:48:15 +0545
Subject: [PATCH] fix: skip empty citation segments after semicolon split

citation() panics with index-out-of-range when input contains empty
segments after splitting on semicolons (e.g. [@;], [@ref;], [@ref1;;@ref2]).

bytes.Split produces empty slices for adjacent/trailing semicolons.
Add a length check before indexing into the trimmed citation slice.
---
 parser/citation.go      |  3 +++
 parser/citation_test.go | 17 +++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/parser/citation.go b/parser/citation.go
index 217d4def..5790e22a 100644
--- a/parser/citation.go
+++ b/parser/citation.go
@@ -49,6 +49,9 @@ func citation(p *Parser, data []byte, offset int) (int, ast.Node) {
 	for _, citation := range citations {
 		var suffix []byte
 		citation = bytes.TrimSpace(citation)
+		if len(citation) == 0 {
+			continue
+		}
 		j := 0
 		if citation[j] != '@' {
 			// not a citation, drop out entirely.
diff --git a/parser/citation_test.go b/parser/citation_test.go
index 635d6f30..b6e0e51b 100644
--- a/parser/citation_test.go
+++ b/parser/citation_test.go
@@ -43,6 +43,23 @@ func TestCitationSuffix(t *testing.T) {
 	}
 }
 
+func TestCitationEmptySegment(t *testing.T) {
+	p := New()
+	p.extensions |= Mmark
+
+	// These inputs should not panic
+	inputs := [][]byte{
+		[]byte(`[@;]`),
+		[]byte(`[@ref;]`),
+		[]byte(`[@ref1;;@ref2]`),
+	}
+	for _, data := range inputs {
+		_, node := citation(p, data, 0)
+		// empty segments are skipped; result depends on remaining valid citations
+		_ = node
+	}
+}
+
 func TestCitationSuffixMultiple(t *testing.T) {
 	data := []byte(`[@?RFC1034; @!RFC1035, p. 144, more]`)