feat: add checkFootnoteDefinitions option to no-empty-definitions

docs/rules/no-empty-definitions.md

@@ -4,19 +4,27 @@ Disallow empty definitions.
 
 ## Background
 
-Markdown allows you to specify a label as a placeholder for a URL in both links and images using square brackets, such as:
+Markdown allows you to specify a label as a placeholder for a URL in both links and images, or as a footnote reference, using square brackets. For example:
 
 ```markdown
 [ESLint][eslint]
 
 [eslint]: https://eslint.org
+
+[ESLint][^eslint]
+
+[^eslint]: Find and fix problmes in your JavaScript code
 ```
 
-If the definition's URL is empty or only contains an empty fragment (`#`), then it's not providing any useful information and could be a mistake.
+Definitions with an empty URL or only an empty fragment (`#`), as well as footnote definitions with no content, are usually mistakes and do not provide useful information.
 
 ## Rule Details
 
-This rule warns when it finds definitions where the URL is either not specified or contains only an empty fragment (`#`).
+> [!IMPORTANT] <!-- eslint-disable-line -- This should be fixed in https://github.com/eslint/markdown/issues/294 -->
+>
+> Footnotes are only supported when using `language` mode [`markdown/gfm`](/README.md#languages).
+
+This rule warns when it finds definitions where the URL is either not specified or contains only an empty fragment (`#`). It also warns for empty footnote definitions by default.
 
 Examples of **incorrect** code for this rule:
 
@@ -25,15 +33,31 @@ Examples of **incorrect** code for this rule:
 
 [earth]: <>
 [moon]: #
+[^note]:
 ```
 
-Examples of correct code:
+Examples of **correct** code for this rule:
 
 ```markdown
 <!-- eslint markdown/no-empty-definitions: "error" -->
 
 [earth]: https://example.com/earth/
 [moon]: #section
+[^note]: This is a footnote.
+```
+
+## Options
+
+The following options are available on this rule:
+
+* `checkFootnoteDefinitions: boolean` - When set to `false`, the rule will not report empty footnote definitions. (default: `true`).
+
+Examples of **correct** code for this rule with `checkFootnoteDefinitions: false`:
+
+```markdown
+<!-- eslint markdown/no-empty-definitions: ["error", { checkFootnoteDefinitions: false }] -->
+
+[^note]:
 ```
 
 ## When Not to Use It

src/rules/no-empty-definitions.js

@@ -8,10 +8,29 @@
 //-----------------------------------------------------------------------------
 
 /**
- * @typedef {import("../types.ts").MarkdownRuleDefinition<{ RuleOptions: []; }>}
- * NoEmptyDefinitionsRuleDefinition
+ * @import { MarkdownRuleDefinition } from "../types.js";
+ * @typedef {"emptyDefinition" | "emptyFootnoteDefinition"} NoEmptyDefinitionsMessageIds
+ * @typedef {[{ checkFootnoteDefinitions?: boolean }]} NoEmptyDefinitionsOptions
+ * @typedef {MarkdownRuleDefinition<{ RuleOptions: NoEmptyDefinitionsOptions, MessageIds: NoEmptyDefinitionsMessageIds }>} NoEmptyDefinitionsRuleDefinition
  */
 
+//-----------------------------------------------------------------------------
+// Helpers
+//-----------------------------------------------------------------------------
+
+const htmlCommentPattern = /<!--[\s\S]*?-->/gu;
+
+/**
+ * Checks if a string contains only HTML comments.
+ * @param {string} value The input string to check.
+ * @returns {boolean} True if the string contains only HTML comments, false otherwise.
+ */
+function isOnlyComments(value) {
+	const withoutComments = value.replace(htmlCommentPattern, "");
+
+	return withoutComments.trim().length === 0;
+}
+
 //-----------------------------------------------------------------------------
 // Rule Definition
 //-----------------------------------------------------------------------------
@@ -29,10 +48,28 @@ export default {
 
 		messages: {
 			emptyDefinition: "Unexpected empty definition found.",
+			emptyFootnoteDefinition:
+				"Unexpected empty footnote definition found.",
 		},
+
+		schema: [
+			{
+				type: "object",
+				properties: {
+					checkFootnoteDefinitions: {
+						type: "boolean",
+					},
+				},
+				additionalProperties: false,
+			},
+		],
+
+		defaultOptions: [{ checkFootnoteDefinitions: true }],
 	},
 
 	create(context) {
+		const [{ checkFootnoteDefinitions }] = context.options;
+
 		return {
 			definition(node) {
 				if (!node.url || node.url === "#") {
@@ -42,6 +79,23 @@ export default {
 					});
 				}
 			},
+
+			footnoteDefinition(node) {
+				if (
+					checkFootnoteDefinitions &&
+					(node.children.length === 0 ||
+						node.children.every(
+							child =>
+								child.type === "html" &&
+								isOnlyComments(child.value),
+						))
+				) {
+					context.report({
+						loc: node.position,
+						messageId: "emptyFootnoteDefinition",
+					});
+				}
+			},
 		};
 	},
 };

tests/rules/no-empty-definitions.test.js

@@ -20,7 +20,7 @@ const ruleTester = new RuleTester({
 	plugins: {
 		markdown,
 	},
-	language: "markdown/commonmark",
+	language: "markdown/gfm",
 });
 
 ruleTester.run("no-empty-definitions", rule, {
@@ -29,6 +29,28 @@ ruleTester.run("no-empty-definitions", rule, {
 		"[foo]: #bar",
 		"[foo]: http://bar.com",
 		"[foo]: <https://bar.com>",
+		"[^note]: This is a footnote.",
+		"[^note]: ![]()",
+		"[^note]: [text](url)",
+		"[^note]:\n    Content",
+		"[^note]:\n    > blockquote",
+		"[^note]: <span></span>",
+		"\\[^note]:",
+		"[\\^note]:",
+		"[^note\\]:",
+		"[^note]\\:",
+		"[^foo]: <span></span> <!-- comment -->",
+		"[^foo]: content <!-- comment -->",
+		"[^foo]: <!-- comment --> content",
+		"[^foo]: <!-- comment --> content <!-- comment -->",
+		dedent`
+		[^foo]: <!-- comm
+		    ent --> content <!-- comment -->
+		`,
+		{
+			code: "[^note]:",
+			options: [{ checkFootnoteDefinitions: false }],
+		},
 	],
 	invalid: [
 		{
@@ -77,5 +99,132 @@ ruleTester.run("no-empty-definitions", rule, {
 				},
 			],
 		},
+		{
+			code: "[^note]:",
+			errors: [
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 1,
+					column: 1,
+					endLine: 1,
+					endColumn: 9,
+				},
+			],
+		},
+		{
+			code: "[^note]:   ",
+			errors: [
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 1,
+					column: 1,
+					endLine: 1,
+					endColumn: 12,
+				},
+			],
+		},
+		{
+			code: "[^note]:\n",
+			errors: [
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 1,
+					column: 1,
+					endLine: 1,
+					endColumn: 9,
+				},
+			],
+		},
+		{
+			code: "[^a]:\n[^b]:",
+			errors: [
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 1,
+					column: 1,
+					endLine: 1,
+					endColumn: 6,
+				},
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 2,
+					column: 1,
+					endLine: 2,
+					endColumn: 6,
+				},
+			],
+		},
+		{
+			code: "[foo]: #\n[^note]:",
+			errors: [
+				{
+					messageId: "emptyDefinition",
+					line: 1,
+					column: 1,
+					endLine: 1,
+					endColumn: 9,
+				},
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 2,
+					column: 1,
+					endLine: 2,
+					endColumn: 9,
+				},
+			],
+		},
+		{
+			code: "[foo]: #\n[^note]:",
+			options: [{ checkFootnoteDefinitions: false }],
+			errors: [
+				{
+					messageId: "emptyDefinition",
+					line: 1,
+					column: 1,
+					endLine: 1,
+					endColumn: 9,
+				},
+			],
+		},
+		{
+			code: "[^foo]: <!-- comment -->",
+			errors: [
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 1,
+					column: 1,
+					endLine: 1,
+					endColumn: 25,
+				},
+			],
+		},
+		{
+			code: dedent`
+			[^foo]: <!-- comment
+			    -->`,
+			errors: [
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 1,
+					column: 1,
+					endLine: 2,
+					endColumn: 8,
+				},
+			],
+		},
+		{
+			code: dedent`
+			[^foo]: <!-- comment -->
+			    <!-- another comment -->`,
+			errors: [
+				{
+					messageId: "emptyFootnoteDefinition",
+					line: 1,
+					column: 1,
+					endLine: 2,
+					endColumn: 29,
+				},
+			],
+		},
 	],
 });