fix: check IndexByte return before adding in tagLength

tagLength() adds the return value of bytes.IndexByte directly to the
current index. When '>' is not found, IndexByte returns -1, which
decrements i instead of making it negative. The guard `if i < 0`
never triggers, causing leftAngle() to silently skip characters.

Store the IndexByte result in a separate variable and check it before
adding to i.

Author: vnykmshr

inline_test.go

@@ -1286,6 +1286,14 @@ func TestSkipHTML(t *testing.T) {
 	}, TestParams{Flags: html.SkipHTML})
 }
 
+func TestTagLengthUnclosedAngle(t *testing.T) {
+	// Unclosed angle brackets with short tag names should not lose content
+	doTestsParam(t, []string{
+		"click <a href content",
+		"<p>click &lt;a href content</p>\n",
+	}, TestParams{Flags: html.SkipHTML})
+}
+
 func TestInlineMath(t *testing.T) {
 	doTestsParam(t, []string{
 		"$a_b$",

parser/inline.go

@@ -1073,10 +1073,11 @@ func tagLength(data []byte) (autolink autolinkType, end int) {
 		// one of the forbidden chars has been found
 		autolink = notAutolink
 	}
-	i += bytes.IndexByte(data[i:], '>')
-	if i < 0 {
+	j = bytes.IndexByte(data[i:], '>')
+	if j < 0 {
 		return autolink, 0
 	}
+	i += j
 	return autolink, i + 1
 }