From d688a1d9ebbeac1dba1e51863d480640e420ae55 Mon Sep 17 00:00:00 2001
From: SAY-5 <say.apm35@gmail.com>
Date: Tue, 12 May 2026 11:22:06 -0700
Subject: [PATCH] fix: avoid panic formatting processing instructions without
 attributes

FormatXml indexed attrComponents[1] unconditionally when splitting a
processing instruction's pseudo-attributes on '=', causing an index out
of range panic for instructions like <?xml-stylesheet?> or any PI whose
body is empty or lacks an '=' separator.
---
 internal/utils/utils.go         | 14 ++++++++++----
 internal/utils/utils_test.go    |  1 +
 test/data/xml/formatted17.xml   |  8 ++++++++
 test/data/xml/unformatted17.xml |  4 ++++
 4 files changed, 23 insertions(+), 4 deletions(-)
 create mode 100644 test/data/xml/formatted17.xml
 create mode 100644 test/data/xml/unformatted17.xml

diff --git a/internal/utils/utils.go b/internal/utils/utils.go
index 2597b2a..ea7b479 100644
--- a/internal/utils/utils.go
+++ b/internal/utils/utils.go
@@ -94,10 +94,16 @@ func FormatXml(reader io.Reader, writer io.Writer, indent string, colors int) er
 			_, _ = fmt.Fprintf(writer, "%s%s", tagColor("<?"), typedToken.Target)
 
 			pi := strings.TrimSpace(string(typedToken.Inst))
-			attrs := strings.Split(pi, " ")
-			for _, attr := range attrs {
-				attrComponents := strings.SplitN(attr, "=", 2)
-				_, _ = fmt.Fprintf(writer, " %s%s", attrComponents[0], attrColor("="+attrComponents[1]))
+			if pi != "" {
+				attrs := strings.Split(pi, " ")
+				for _, attr := range attrs {
+					attrComponents := strings.SplitN(attr, "=", 2)
+					if len(attrComponents) == 2 {
+						_, _ = fmt.Fprintf(writer, " %s%s", attrComponents[0], attrColor("="+attrComponents[1]))
+					} else {
+						_, _ = fmt.Fprintf(writer, " %s", attrComponents[0])
+					}
+				}
 			}
 
 			_, _ = fmt.Fprint(writer, tagColor("?>"), newline)
diff --git a/internal/utils/utils_test.go b/internal/utils/utils_test.go
index b0ffd78..b3116ea 100644
--- a/internal/utils/utils_test.go
+++ b/internal/utils/utils_test.go
@@ -39,6 +39,7 @@ func TestFormatXml(t *testing.T) {
 		"unformatted14.xml": "formatted14.xml",
 		"unformatted15.xml": "formatted15.xml",
 		"unformatted16.xml": "formatted16.xml",
+		"unformatted17.xml": "formatted17.xml",
 	}
 
 	for unformattedFile, expectedFile := range files {
diff --git a/test/data/xml/formatted17.xml b/test/data/xml/formatted17.xml
new file mode 100644
index 0000000..56af9ae
--- /dev/null
+++ b/test/data/xml/formatted17.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<?xml-stylesheet?>
+<?xml-stylesheet type="text/xsl" href="style.xsl"?>
+<rss>
+  <channel>
+    <title>Test</title>
+  </channel>
+</rss>
diff --git a/test/data/xml/unformatted17.xml b/test/data/xml/unformatted17.xml
new file mode 100644
index 0000000..37933bc
--- /dev/null
+++ b/test/data/xml/unformatted17.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<?xml-stylesheet?>
+<?xml-stylesheet type="text/xsl" href="style.xsl"?>
+<rss><channel><title>Test</title></channel></rss>