Add missing link about custom message option to rule docs (#6475)

This change also adds test cases to prevent such mistakes.

lib/rules/__tests__/index.test.js

@@ -31,3 +31,20 @@ describe('fixable rules', () => {
 		expect(rulesListDoc).toMatch(new RegExp(`^.+\\b${name}\\b.+\\(Autofixable\\)\\.$`, 'm'));
 	});
 });
+
+describe('custom message option', () => {
+	test.each(Object.keys(rules))(
+		'"%s" should describe a custom message option in the doc',
+		async (ruleName) => {
+			const jsFile = path.join(__dirname, '..', ruleName, 'index.js');
+			const jsCode = await fs.promises.readFile(jsFile, 'utf8');
+
+			// NOTE: If all rules support a custom message option, we should remove this `if` statement.
+			if (!jsCode.includes('\tmessageArgs: [')) return;
+
+			const doc = await fs.promises.readFile(jsFile.replace('index.js', 'README.md'), 'utf8');
+
+			expect(doc).toContain('`message` secondary option');
+		},
+	);
+});

lib/rules/custom-media-pattern/README.md

@@ -9,6 +9,8 @@ Specify a pattern for custom media query names.
  * The pattern of this */
 ```
 
+The [`message` secondary option](../../../docs/user-guide/configure.md#message) can accept the arguments of this rule.
+
 ## Options
 
 `regex|string`

lib/rules/custom-property-pattern/README.md

@@ -9,6 +9,8 @@ a { --foo-: 1px; }
  * The pattern of this */
 ```
 
+The [`message` secondary option](../../../docs/user-guide/configure.md#message) can accept the arguments of this rule.
+
 ## Options
 
 `regex|string`

lib/rules/keyframes-name-pattern/README.md

@@ -9,6 +9,8 @@ Specify a pattern for keyframe names.
  * The pattern of this */
 ```
 
+The [`message` secondary option](../../../docs/user-guide/configure.md#message) can accept the arguments of this rule.
+
 ## Options
 
 `regex|string`

lib/rules/selector-class-pattern/README.md

@@ -13,6 +13,8 @@ This rule ignores non-outputting Less mixin definitions and called Less mixins.
 
 Escaped selectors (e.g. `.u-size-11\/12\@sm`) are parsed as escaped twice (e.g. `.u-size-11\\/12\\@sm`). Your RegExp should account for that.
 
+The [`message` secondary option](../../../docs/user-guide/configure.md#message) can accept the arguments of this rule.
+
 ## Options
 
 `regex|string`

lib/rules/selector-id-pattern/README.md

@@ -9,6 +9,8 @@ Specify a pattern for ID selectors.
  * These ID selectors */
 ```
 
+The [`message` secondary option](../../../docs/user-guide/configure.md#message) can accept the arguments of this rule.
+
 ## Options
 
 `regex|string`

lib/rules/selector-nested-pattern/README.md

@@ -14,6 +14,8 @@ Specify a pattern for the selectors of rules nested within rules.
 
 Non-standard selectors (e.g. selectors with Sass or Less interpolation) and selectors of rules nested within at-rules are ignored.
 
+The [`message` secondary option](../../../docs/user-guide/configure.md#message) can accept the arguments of this rule.
+
 ## Options
 
 `regex|string`