Update MD053/link-image-reference-definitions to add ignored_definiti…

…ons parameter (default to ["//"]) (fixes #545).

demo/markdownlint-browser.js

@@ -3658,7 +3658,7 @@ module.exports = {
                     if (!linkDestinationRe.test(prefix)) {
                         const unescaped = unescapeMarkdown(prefix + "<", "_");
                         if (!unescaped.endsWith("_")) {
-                            addError(onError, lineIndex + 1, "Element: " + element, null, [match.index + 1, tag.length]);
+                            addError(onError, lineIndex + 1, "Element: " + element, undefined, [match.index + 1, tag.length]);
                         }
                     }
                 }
@@ -4727,7 +4727,8 @@ module.exports = {
     "description": "Link and image reference definitions should be needed",
     "tags": ["images", "links"],
     "function": function MD053(params, onError) {
-        const { lines } = params;
+        const ignored = new Set(params.config.ignored_definitions || ["//"]);
+        const lines = params.lines;
         const { references, shortcuts, definitions, duplicateDefinitions } = referenceLinkImageData();
         const singleLineDefinition = (line) => (line.replace(linkReferenceDefinitionRe, "").trim().length > 0);
         const deleteFixInfo = {
@@ -4736,16 +4737,20 @@ module.exports = {
         // Look for unused link references (unreferenced by any link/image)
         for (const definition of definitions.entries()) {
             const [label, lineIndex] = definition;
-            if (!references.has(label) && !shortcuts.has(label)) {
+            if (!ignored.has(label) &&
+                !references.has(label) &&
+                !shortcuts.has(label)) {
                 const line = lines[lineIndex];
                 addError(onError, lineIndex + 1, `Unused link or image reference definition: "${label}"`, ellipsify(line), [1, line.length], singleLineDefinition(line) ? deleteFixInfo : 0);
             }
         }
         // Look for duplicate link references (defined more than once)
         for (const duplicateDefinition of duplicateDefinitions) {
             const [label, lineIndex] = duplicateDefinition;
-            const line = lines[lineIndex];
-            addError(onError, lineIndex + 1, `Duplicate link or image reference definition: "${label}"`, ellipsify(line), [1, line.length], singleLineDefinition(line) ? deleteFixInfo : 0);
+            if (!ignored.has(label)) {
+                const line = lines[lineIndex];
+                addError(onError, lineIndex + 1, `Duplicate link or image reference definition: "${label}"`, ellipsify(line), [1, line.length], singleLineDefinition(line) ? deleteFixInfo : 0);
+            }
         }
     }
 };

doc/Rules.md

@@ -1315,7 +1315,7 @@ To fix this, use 'pure' Markdown instead of including raw HTML:
 # Markdown heading
 ```
 
-Note: To allow specific HTML elements, use the 'allowed_elements' parameter.
+Note: To allow specific HTML elements, use the `allowed_elements` parameter.
 
 Rationale: Raw HTML is allowed in Markdown, but this rule is included for
 those who want their documents to only include "pure" Markdown, or for those
@@ -2075,6 +2075,8 @@ Tags: images, links
 
 Aliases: link-image-reference-definitions
 
+Parameters: ignored_definitions (array of string; default [ "//" ])
+
 Fixable: Most violations can be fixed by tooling
 
 Links and images in Markdown can provide the link destination or image source
@@ -2092,9 +2094,18 @@ unnecessary:
    used and the others can be deleted.
 
 This rule considers a reference definition to be used if any link or image
-reference has the corresponding label. "Full", "collapsed", and "shortcut"
+reference has the corresponding label. The "full", "collapsed", and "shortcut"
 formats are all supported.
 
+If there are reference definitions that are deliberately unreferenced, they can
+be ignored by setting the `ignored_definitions` parameter. The default value of
+this parameter ignores the following convention for adding non-HTML comments to
+Markdown:
+
+```md
+[//]: # (This behaves like a comment)
+```
+
 <!-- markdownlint-configure-file {
   "no-inline-html": {
     "allowed_elements": [

lib/md033.js

@@ -38,7 +38,7 @@ module.exports = {
             const unescaped = unescapeMarkdown(prefix + "<", "_");
             if (!unescaped.endsWith("_")) {
               addError(onError, lineIndex + 1, "Element: " + element,
-                null, [ match.index + 1, tag.length ]);
+                undefined, [ match.index + 1, tag.length ]);
             }
           }
         }

lib/md053.js

@@ -11,7 +11,8 @@ module.exports = {
   "description": "Link and image reference definitions should be needed",
   "tags": [ "images", "links" ],
   "function": function MD053(params, onError) {
-    const { lines } = params;
+    const ignored = new Set(params.config.ignored_definitions || [ "//" ]);
+    const lines = params.lines;
     const { references, shortcuts, definitions, duplicateDefinitions } =
       referenceLinkImageData();
     const singleLineDefinition = (line) => (
@@ -23,7 +24,11 @@ module.exports = {
     // Look for unused link references (unreferenced by any link/image)
     for (const definition of definitions.entries()) {
       const [ label, lineIndex ] = definition;
-      if (!references.has(label) && !shortcuts.has(label)) {
+      if (
+        !ignored.has(label) &&
+        !references.has(label) &&
+        !shortcuts.has(label)
+      ) {
         const line = lines[lineIndex];
         addError(
           onError,
@@ -38,15 +43,17 @@ module.exports = {
     // Look for duplicate link references (defined more than once)
     for (const duplicateDefinition of duplicateDefinitions) {
       const [ label, lineIndex ] = duplicateDefinition;
-      const line = lines[lineIndex];
-      addError(
-        onError,
-        lineIndex + 1,
-        `Duplicate link or image reference definition: "${label}"`,
-        ellipsify(line),
-        [ 1, line.length ],
-        singleLineDefinition(line) ? deleteFixInfo : 0
-      );
+      if (!ignored.has(label)) {
+        const line = lines[lineIndex];
+        addError(
+          onError,
+          lineIndex + 1,
+          `Duplicate link or image reference definition: "${label}"`,
+          ellipsify(line),
+          [ 1, line.length ],
+          singleLineDefinition(line) ? deleteFixInfo : 0
+        );
+      }
     }
   }
 };

schema/.markdownlint.jsonc

@@ -275,5 +275,10 @@
   "MD052": true,
 
   // MD053/link-image-reference-definitions - Link and image reference definitions should be needed
-  "MD053": true
+  "MD053": {
+    // Ignored definitions
+    "ignored_definitions": [
+      "//"
+    ]
+  }
 }

schema/.markdownlint.yaml

@@ -249,4 +249,8 @@ MD051: true
 MD052: true
 
 # MD053/link-image-reference-definitions - Link and image reference definitions should be needed
-MD053: true
+MD053:
+  # Ignored definitions
+  ignored_definitions: [
+    "//"
+  ]

schema/build-config-schema.js

@@ -463,6 +463,18 @@ for (const rule of rules) {
         }
       };
       break;
+    case "MD053":
+      scheme.properties = {
+        "ignored_definitions": {
+          "description": "Ignored definitions",
+          "type": "array",
+          "items": {
+            "type": "string"
+          },
+          "default": [ "//" ]
+        }
+      };
+      break;
     default:
       custom = false;
       break;

schema/markdownlint-config-schema.json

@@ -909,8 +909,24 @@
     },
     "MD053": {
       "description": "MD053/link-image-reference-definitions - Link and image reference definitions should be needed",
-      "type": "boolean",
-      "default": true
+      "type": [
+        "boolean",
+        "object"
+      ],
+      "default": true,
+      "properties": {
+        "ignored_definitions": {
+          "description": "Ignored definitions",
+          "type": "array",
+          "items": {
+            "type": "string"
+          },
+          "default": [
+            "//"
+          ]
+        }
+      },
+      "additionalProperties": false
     },
     "link-image-reference-definitions": {
       "$ref": "#/properties/MD053"

test/markdownlint-test.js

@@ -921,7 +921,7 @@ test("readme", (t) => new Promise((resolve) => {
 }));
 
 test("rules", (t) => new Promise((resolve) => {
-  t.plan(373);
+  t.plan(374);
   fs.readFile("doc/Rules.md", "utf8",
     (err, contents) => {
       t.falsy(err);

test/reference-links-and-images.md

@@ -166,6 +166,12 @@ https://example.com/multi-line-label
 [unique6]: https://example.com/unique6
 [unique7]: https://example.com/unique7
 
+## Ignored Labels
+
+[//]: # (This is a technique for putting comments in Markdown)
+
+[//]: <> (Here is another variant)
+
 ## Invalid Labels
 
 Duplicate:

test/reference-links-ignored-definitions-empty.md

@@ -0,0 +1,13 @@
+# Reference Links Ignored Definitions (Empty)
+
+Used reference link: [label]
+
+[label]: https://example.com/label
+[oops]: https://example.com/{MD053}
+[//]: <> ({MD053})
+
+<!-- markdownlint-configure-file {
+  "link-image-reference-definitions": {
+    "ignored_definitions": []
+  }
+} -->

test/reference-links-ignored-definitions.md

@@ -0,0 +1,17 @@
+# Reference Links Ignored Definitions
+
+Used reference link: [label]
+
+[label]: https://example.com/label
+[oops]: https://example.com/{MD053}
+[okay]: https://example.com/ignored
+[yep]: https://example.com/ignored
+
+<!-- markdownlint-configure-file {
+  "link-image-reference-definitions": {
+    "ignored_definitions": [
+      "okay",
+      "yep"
+    ]
+  }
+} -->