feat: new rule attr-value-no-duplication

src/core/rules/attr-value-no-duplication.ts

@@ -0,0 +1,37 @@
+import { Rule } from '../types'
+
+export default {
+  id: 'attr-value-no-duplication',
+  description: 'Attribute values should not contain duplicates.',
+  init(parser, reporter) {
+    parser.addListener('tagstart', (event) => {
+      const attrs = event.attrs
+      let attr
+      const col = event.col + event.tagName.length + 1
+
+      for (let i = 0, l = attrs.length; i < l; i++) {
+        attr = attrs[i]
+
+        if (attr.value) {
+          // Split attribute value by whitespace to get individual values
+          const values = attr.value.trim().split(/\s+/)
+          const duplicateMap: { [value: string]: boolean } = {}
+
+          for (const value of values) {
+            if (duplicateMap[value] === true) {
+              reporter.error(
+                `Duplicate value [ ${value} ] was found in attribute [ ${attr.name} ].`,
+                event.line,
+                col + attr.index,
+                this,
+                attr.raw
+              )
+              break // Only report the first duplicate found per attribute
+            }
+            duplicateMap[value] = true
+          }
+        }
+      }
+    })
+  },
+} as Rule

src/core/rules/index.ts

@@ -2,6 +2,7 @@ export { default as altRequire } from './alt-require'
 export { default as attrLowercase } from './attr-lowercase'
 export { default as attrNoDuplication } from './attr-no-duplication'
 export { default as attrNoUnnecessaryWhitespace } from './attr-no-unnecessary-whitespace'
+export { default as attrValueNoDuplication } from './attr-value-no-duplication'
 export { default as attrSort } from './attr-sorted'
 export { default as attrUnsafeChars } from './attr-unsafe-chars'
 export { default as attrValueDoubleQuotes } from './attr-value-double-quotes'

src/core/types.ts

@@ -17,6 +17,7 @@ export interface Ruleset {
   'attr-value-double-quotes'?: boolean
   'attr-value-not-empty'?: boolean
   'attr-value-single-quotes'?: boolean
+  'attr-value-no-duplication'?: boolean
   'attr-whitespace'?: boolean
   'doctype-first'?: boolean
   'doctype-html5'?: boolean

test/cli/formatters/sarif.sarif

@@ -15,7 +15,7 @@
               "helpUri": "https://htmlhint.com/rules/attr-value-double-quotes",
               "help": {
                 "text": "Attribute values must be in double quotes.",
-                "markdown": "\nAttribute value must closed by double quotes.\n\nLevel: Error\n\n## Config value\n\n1. true: enable rule\n2. false: disable rule\n\n### The following patterns are **not** considered rule violations\n\n```html\n`<a href=\"\" title=\"abc\">``</a>`\n```\n\n### The following pattern is considered a rule violation:\n\n```html\n`<a href='' title='abc'>``</a>`\n```"
+                "markdown": "\nAttribute value must closed by double quotes.\n\nLevel: Error\n\n## Config value\n\n- `true`: enable rule\n- `false`: disable rule\n\n### The following patterns are **not** considered rule violations\n\n```html\n`<a href=\"\" title=\"abc\">``</a>`\n```\n\n### The following pattern is considered a rule violation:\n\n```html\n`<a href='' title='abc'>``</a>`\n```"
               }
             },
             {
@@ -26,7 +26,7 @@
               "helpUri": "https://htmlhint.com/rules/attr-no-duplication",
               "help": {
                 "text": "Elements cannot have duplicate attributes.",
-                "markdown": "\nThe same attribute can't be specified twice.\n\nLevel: Error\n\n## Config value\n\n1. true: enable rule\n2. false: disable rule\n\n### The following patterns are **not** considered rule violations\n\n```html\n`<img src=\"a.png\" />`\n```\n\n### The following pattern is considered a rule violation:\n\n```html\n`<img src=\"a.png\" src=\"b.png\" />`\n```"
+                "markdown": "\nThe same attribute can't be specified twice.\n\nLevel: Error\n\n## Config value\n\n- `true`: enable rule\n- `false`: disable rule\n\n### The following patterns are **not** considered rule violations\n\n```html\n`<img src=\"a.png\" />`\n```\n\n### The following pattern is considered a rule violation:\n\n```html\n`<img src=\"a.png\" src=\"b.png\" />`\n```"
               }
             },
             {
@@ -37,7 +37,7 @@
               "helpUri": "https://htmlhint.com/rules/tag-pair",
               "help": {
                 "text": "Tag must be paired.",
-                "markdown": "\nTag must be paired.\n\nLevel: Error\n\n## Config value\n\n1. true: enable rule\n2. false: disable rule\n\n### The following patterns are **not** considered rule violations\n\n```html\n`<ul>``<li>``</li>``</ul>`\n```\n\n### The following pattern is considered a rule violation:\n\n```html\n`<ul>``<li>``</ul>`\n`<ul>``</li>``</ul>`\n```"
+                "markdown": "\nTag must be paired.\n\nLevel: Error\n\n## Config value\n\n- `true`: enable rule\n- `false`: disable rule\n\n### The following patterns are **not** considered rule violations\n\n```html\n`<ul>``<li>``</li>``</ul>`\n```\n\n### The following pattern is considered a rule violation:\n\n```html\n`<ul>``<li>``</ul>`\n`<ul>``</li>``</ul>`\n```"
               }
             },
             {
@@ -48,7 +48,7 @@
               "helpUri": "https://htmlhint.com/rules/spec-char-escape",
               "help": {
                 "text": "Special characters must be escaped.",
-                "markdown": "\nSpecial characters must be escaped.\n\nLevel: Error\n\n## Config value\n\n1. true: enable rule\n2. false: disable rule\n\n### The following patterns are **not** considered violations\n\n```html\n`<span>`aaa&gt;bbb&lt;ccc`</span>`\n`<span>`Steinway &amp; Sons, Q&amp;A`</span>`\n`<span>`Steinway & Sons, Q&A`</span>`\n```\n\n### The following pattern is considered a rule violation:\n\n```html\n`<span>`aaa>bbb`<ccc</span>`\n```"
+                "markdown": "\nSpecial characters must be escaped.\n\nLevel: Error\n\n## Config value\n\n- `true`: enable rule\n- `false`: disable rule\n\n### The following patterns are **not** considered violations\n\n```html\n`<span>`aaa&gt;bbb&lt;ccc`</span>`\n`<span>`Steinway &amp; Sons, Q&amp;A`</span>`\n`<span>`Steinway & Sons, Q&A`</span>`\n```\n\n### The following pattern is considered a rule violation:\n\n```html\n`<span>`aaa>bbb`<ccc</span>`\n```"
               }
             }
           ],

test/rules/attr-value-no-duplication.spec.js

@@ -0,0 +1,67 @@
+const HTMLHint = require('../../dist/htmlhint.js').HTMLHint
+
+const ruleId = 'attr-value-no-duplication'
+const ruleOptions = {}
+
+ruleOptions[ruleId] = true
+
+describe(`Rules: ${ruleId}`, () => {
+  it('Duplicate values in class attribute should result in an error', () => {
+    const code = '<div class="d-none small d-none">Test</div>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).toBe(1)
+    expect(messages[0].rule.id).toBe(ruleId)
+    expect(messages[0].line).toBe(1)
+    expect(messages[0].col).toBe(5)
+    expect(messages[0].message).toBe(
+      'Duplicate value [ d-none ] was found in attribute [ class ].'
+    )
+  })
+
+  it('Duplicate values in data attribute should result in an error', () => {
+    const code = '<span data-attributes="dark light dark">Test</span>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).toBe(1)
+    expect(messages[0].rule.id).toBe(ruleId)
+    expect(messages[0].line).toBe(1)
+    expect(messages[0].col).toBe(6)
+    expect(messages[0].message).toBe(
+      'Duplicate value [ dark ] was found in attribute [ data-attributes ].'
+    )
+  })
+
+  it('No duplicate values should not result in an error', () => {
+    const code = '<div class="container fluid small">Test</div>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).toBe(0)
+  })
+
+  it('Single value should not result in an error', () => {
+    const code = '<div class="container">Test</div>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).toBe(0)
+  })
+
+  it('Empty attribute value should not result in an error', () => {
+    const code = '<div class="">Test</div>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).toBe(0)
+  })
+
+  it('Multiple attributes with no duplicates should not result in an error', () => {
+    const code =
+      '<div class="btn btn-primary" id="submit-button" data-toggle="modal">Test</div>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).toBe(0)
+  })
+
+  it('Multiple spaces between values should still detect duplicates', () => {
+    const code = '<div class="btn    primary   btn">Test</div>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).toBe(1)
+    expect(messages[0].rule.id).toBe(ruleId)
+    expect(messages[0].message).toBe(
+      'Duplicate value [ btn ] was found in attribute [ class ].'
+    )
+  })
+})

website/src/content/docs/rules/attr-value-no-duplication.mdx

@@ -0,0 +1,59 @@
+---
+id: attr-value-no-duplication
+title: attr-value-no-duplication
+description: Prevents duplicate values within the same attribute to ensure clean and efficient markup.
+draft: true
+sidebar:
+  badge: New
+
+---
+
+import { Badge } from '@astrojs/starlight/components';
+
+Attribute values should not contain duplicates.
+
+Level: <Badge text="Error" variant="danger" />
+
+## Config value
+
+- `true`: enable rule
+- `false`: disable rule
+
+### The following patterns are **not** considered rule violations
+
+```html
+<div class="container fluid small">Content</div>
+```
+
+```html
+<span data-toggle="modal">Content</span>
+```
+
+```html
+<div class="btn btn-primary btn-large">Button</div>
+```
+
+### The following patterns are considered rule violations:
+
+```html
+<div class="d-none small d-none">Content</div>
+```
+
+```html
+<span data-attributes="dark light dark">Content</span>
+```
+
+```html
+<div class="btn    primary   btn">Button</div>
+```
+
+## Why does this rule exist?
+
+Having duplicate values in attributes like `class` or custom data attributes can:
+
+- Make the markup unnecessarily verbose
+- Cause confusion during development
+- Lead to inefficient CSS specificity calculations
+- Indicate potential copy-paste errors or oversight
+
+This rule helps maintain clean, efficient markup by catching these duplicates early.

website/src/content/docs/rules/index.mdx

@@ -31,6 +31,8 @@ description: A complete list of all the rules for HTMLHint
 - [`button-type-require`](button-type-require/): The type attribute of a button element must be present with a valid value: "button", "submit", or "reset".
 - [`input-requires-label`](input-requires-label/): All [ input ] tags must have a corresponding [ label ] tag.
 
+{/* [`attr-value-no-duplication`](attr-value-no-duplication/): Attribute values should not contain duplicates. */}
+
 ## Tags
 
 - [`empty-tag-not-self-closed`](empty-tag-not-self-closed/): The empty tag should not be closed by self.