HTML export: Improve handling of missing footnote definitions

org/html_writer.go

@@ -151,6 +151,16 @@ func (w *HTMLWriter) WriteFootnotes(d *Document) {
 	w.WriteString(`<hr class="footnotes-separatator">` + "\n")
 	w.WriteString(`<div class="footnote-definitions">` + "\n")
 	for i, definition := range w.footnotes.list {
+		if definition == nil {
+			name := ""
+			for k, v := range w.footnotes.mapping {
+				if v == i {
+					name = k
+				}
+			}
+			w.log.Printf("Missing footnote definition for [fn:%s] (#%d)", name, i)
+			continue
+		}
 		w.WriteString(`<div class="footnote-definition">` + "\n")
 		w.WriteString(fmt.Sprintf(`<sup id="footnote-%d"><a href="#footnote-reference-%d">%d</a></sup>`, i, i, i) + "\n")
 		w.WriteString(`<div class="footnote-body">` + "\n")

org/testdata/footnotes.html

@@ -36,15 +36,20 @@ Footnote definitions are not printed where they appear.
 Rather, they are gathered and exported at the end of the document in the footnote section. <sup class="footnote-reference"><a id="footnote-reference-5" href="#footnote-5">5</a></sup>
 </p>
 </li>
+<li>
+<p>
+footnotes that reference a non-existant definition are rendered but log a warning <sup class="footnote-reference"><a id="footnote-reference-6" href="#footnote-6">6</a></sup>
+</p>
+</li>
 </ul>
 <h1 id="headline-2">
 Footnotes
 </h1>
 <p>
-Please note that the footnotes section is not automatically excluded from the export like in emacs. <sup class="footnote-reference"><a id="footnote-reference-6" href="#footnote-6">6</a></sup>
+Please note that the footnotes section is not automatically excluded from the export like in emacs. <sup class="footnote-reference"><a id="footnote-reference-7" href="#footnote-7">7</a></sup>
 </p>
 <p>
-this is not part of <sup class="footnote-reference"><a id="footnote-reference-6" href="#footnote-6">6</a></sup> anymore as there are 2 blank lines in between!
+this is not part of <sup class="footnote-reference"><a id="footnote-reference-7" href="#footnote-7">7</a></sup> anymore as there are 2 blank lines in between!
 </p>
 <div class="footnotes">
 <hr class="footnotes-separatator">
@@ -147,7 +152,7 @@ Rather, it will be somewhere down below in the footnotes section.
 </div>
 </div>
 <div class="footnote-definition">
-<sup id="footnote-6"><a href="#footnote-reference-6">6</a></sup>
+<sup id="footnote-7"><a href="#footnote-reference-7">7</a></sup>
 <div class="footnote-body">
 <p>
 There&#39;s multiple reasons for that. Among others, doing so requires i18n (to recognize the section) and silently

org/testdata/footnotes.org

@@ -5,6 +5,7 @@
 - anonymous inline footnotes are also supported via [fn::the anonymous inline footnote definition].
 - Footnote definitions are not printed where they appear.
   Rather, they are gathered and exported at the end of the document in the footnote section. [fn:4]
+- footnotes that reference a non-existant definition are rendered but log a warning [fn:does-not-exist]
 
 [fn:4] so this definition will not be at the end of this section in the exported document.
 Rather, it will be somewhere down below in the footnotes section.

org/testdata/footnotes.pretty_org

@@ -5,6 +5,7 @@
 - anonymous inline footnotes are also supported via [fn::the anonymous inline footnote definition].
 - Footnote definitions are not printed where they appear.
   Rather, they are gathered and exported at the end of the document in the footnote section. [fn:4]
+- footnotes that reference a non-existant definition are rendered but log a warning [fn:does-not-exist]
 
 [fn:4] so this definition will not be at the end of this section in the exported document.
 Rather, it will be somewhere down below in the footnotes section.