Disallow link when a footnote is nested inside it

Fixes #400.

Author: robinst

CHANGELOG.md

@@ -7,9 +7,16 @@ This project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html
 with the exception that 0.x versions can break between minor versions.
 
 ## Unreleased
+### Changed
+- A `LinkProcessor` using `replaceWith` now also stops outer links from being
+  parsed as links, same as with `wrapTextIn`. This prevents nested links, see
+  footnotes change below.
 ### Fixed
-
 - Fix rendering of image alt text to include contents of code spans (`` `code` ``). (#398)
+- footnotes: Fix footnotes nested within links. Before, both the link and the
+  footnote reference would be parsed and lead to nested `<a>` elements, which
+  is disallowed. Now, only the footnote is parsed and the outer link becomes
+  plain text; this matches the behavior of links. (#400)
 
 ## [0.25.1] - 2025-08-01
 ### Fixed

commonmark-ext-footnotes/src/test/java/org/commonmark/ext/footnotes/FootnotesTest.java

@@ -254,6 +254,29 @@ public void testReferenceLinkWithoutDefinition() {
         assertText("[foo]", paragraph.getLastChild());
     }
 
+    @Test
+    public void testFootnoteInLink() {
+        // Expected to behave the same way as a link within a link, see https://spec.commonmark.org/0.31.2/#example-518
+        // i.e. the first (inner) link is parsed, which means the outer one becomes plain text, as nesting links is not
+        // allowed.
+        var doc = PARSER.parse("[link with footnote ref [^1]](https://example.com)\n\n[^1]: footnote\n");
+        var ref = find(doc, FootnoteReference.class);
+        assertThat(ref.getLabel()).isEqualTo("1");
+        var paragraph = doc.getFirstChild();
+        assertText("[link with footnote ref ", paragraph.getFirstChild());
+        assertText("](https://example.com)", paragraph.getLastChild());
+    }
+
+    @Test
+    public void testFootnoteWithMarkerInLink() {
+        var doc = PARSER.parse("[link with footnote ref ![^1]](https://example.com)\n\n[^1]: footnote\n");
+        var ref = find(doc, FootnoteReference.class);
+        assertThat(ref.getLabel()).isEqualTo("1");
+        var paragraph = doc.getFirstChild();
+        assertText("[link with footnote ref !", paragraph.getFirstChild());
+        assertText("](https://example.com)", paragraph.getLastChild());
+    }
+
     @Test
     public void testInlineFootnote() {
         var extension = FootnotesExtension.builder().inlineFootnotes(true).build();

commonmark/src/main/java/org/commonmark/internal/InlineParserImpl.java

@@ -440,16 +440,9 @@ private Node wrapBracket(Bracket opener, Node wrapperNode, boolean includeMarker
         opener.bracketNode.unlink();
         removeLastBracket();
 
-        // Links within links are not allowed. We found this link, so there can be no other link around it.
+        // Links within links are not allowed. We found this link, so there can be no other links around it.
         if (opener.markerNode == null) {
-            Bracket bracket = lastBracket;
-            while (bracket != null) {
-                if (bracket.markerNode == null) {
-                    // Disallow link opener. It will still get matched, but will not result in a link.
-                    bracket.allowed = false;
-                }
-                bracket = bracket.previous;
-            }
+            disallowPreviousLinks();
         }
 
         return wrapperNode;
@@ -475,6 +468,15 @@ private Node replaceBracket(Bracket opener, Node node, boolean includeMarker) {
             n.unlink();
             n = next;
         }
+
+        // Links within links are not allowed. We found this link, so there can be no other links around it.
+        // Note that this makes any syntax like `[foo]` behave the same as built-in links, which is probably a good
+        // default (it works for footnotes). It might be useful for a `LinkProcessor` to be able to specify the
+        // behavior; something we could add to `LinkResult` in the future if requested.
+        if (opener.markerNode == null || !includeMarker) {
+            disallowPreviousLinks();
+        }
+
         return node;
     }
 
@@ -489,6 +491,17 @@ private void removeLastBracket() {
         lastBracket = lastBracket.previous;
     }
 
+    private void disallowPreviousLinks() {
+        Bracket bracket = lastBracket;
+        while (bracket != null) {
+            if (bracket.markerNode == null) {
+                // Disallow link opener. It will still get matched, but will not result in a link.
+                bracket.allowed = false;
+            }
+            bracket = bracket.previous;
+        }
+    }
+
     /**
      * Try to parse the destination and an optional title for an inline link/image.
      */