markup/goldmark: Fail on invalid Markdown attributes

common/herrors/error_locator.go

@@ -61,6 +61,16 @@ var OffsetMatcher = func(m LineMatcher) int {
 	return -1
 }
 
+// ContainsMatcher is a line matcher that matches by line content.
+func ContainsMatcher(text string) func(m LineMatcher) int {
+	return func(m LineMatcher) int {
+		if idx := strings.Index(m.Line, text); idx != -1 {
+			return idx + 1
+		}
+		return -1
+	}
+}
+
 // ErrorContext contains contextual information about an error. This will
 // typically be the lines surrounding some problem in a file.
 type ErrorContext struct {

common/herrors/file_error.go

@@ -392,3 +392,17 @@ func extractPosition(e error) (pos text.Position) {
 	}
 	return
 }
+
+// TextSegmentError is an error with a text segment attached.
+type TextSegmentError struct {
+	Segment string
+	Err     error
+}
+
+func (e TextSegmentError) Unwrap() error {
+	return e.Err
+}
+
+func (e TextSegmentError) Error() string {
+	return e.Err.Error()
+}