Add declaration-block-no-duplicate-custom-properties

docs/user-guide/rules/list.md

@@ -41,6 +41,7 @@ Grouped first by the following categories and then by the [_thing_](http://apps.
 
 ### Declaration block
 
+- [`declaration-block-no-duplicate-custom-properties`](../../../lib/rules/declaration-block-no-duplicate-custom-properties/README.md): Disallow duplicate custom properties within declaration blocks.
 - [`declaration-block-no-duplicate-properties`](../../../lib/rules/declaration-block-no-duplicate-properties/README.md): Disallow duplicate properties within declaration blocks.
 - [`declaration-block-no-shorthand-property-overrides`](../../../lib/rules/declaration-block-no-shorthand-property-overrides/README.md): Disallow shorthand properties that override related longhand properties.
 

lib/rules/declaration-block-no-duplicate-custom-properties/README.md

@@ -0,0 +1,40 @@
+# declaration-block-no-duplicate-custom-properties
+
+Disallow duplicate custom properties within declaration blocks.
+
+<!-- prettier-ignore -->
+```css
+a { --custom-property: pink; --custom-property: orange; }
+/** ↑                        ↑
+ * These duplicated custom properties */
+```
+
+This rule is case-sensitive.
+
+## Options
+
+### `true`
+
+The following patterns are considered violations:
+
+<!-- prettier-ignore -->
+```css
+a { --custom-property: pink; --custom-property: orange; }
+```
+
+<!-- prettier-ignore -->
+```css
+a { --custom-property: pink; background: orange; --custom-property: orange }
+```
+
+The following patterns are _not_ considered violations:
+
+<!-- prettier-ignore -->
+```css
+a { --custom-property: pink; }
+```
+
+<!-- prettier-ignore -->
+```css
+a { --custom-property: pink; --cUstOm-prOpErtY: orange; }
+```

lib/rules/declaration-block-no-duplicate-custom-properties/__tests__/index.js

@@ -0,0 +1,165 @@
+'use strict';
+
+const { messages, ruleName } = require('..');
+
+testRule({
+	ruleName,
+	config: [true],
+
+	accept: [
+		{
+			code: 'a { --custom-property: 1 }',
+		},
+		{
+			code: 'a { --custom-property: 1; --cUstOm-prOpErtY: 1 }',
+		},
+		{
+			code: 'a { --custom-property: 1; color: pink; --cUstOm-prOpErtY: 1 }',
+		},
+		{
+			code: 'a { color: var(--custom-property, --custom-property) }',
+		},
+		{
+			code: 'a { --custom-property: pink; @media { --custom-property: orange; } }',
+			description: 'nested',
+		},
+		{
+			code:
+				'a { --custom-property: pink; @media { --custom-property: orange; &::before { --custom-property: black; } } }',
+			description: 'double nested',
+		},
+		{
+			code:
+				'a { --custom-property: pink; { &:hover { --custom-property: orange; --cUstOm-prOpErtY: black; } } }',
+			description: 'spec nested',
+		},
+		{
+			code:
+				'a { --cUstOm-prOpErtY: pink; { &:hover { --custom-property: orange; --cUstOm-prOpErtY: black; } } }',
+			description: 'spec nested',
+		},
+	],
+
+	reject: [
+		{
+			code: 'a { --custom-property: 1; --custom-property: 2; }',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code: 'a { --custom-property: 1; color: pink; --custom-property: 1; }',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code: 'a { --custom-property: 1; --cUstOm-prOpErtY: 1; color: pink; --cUstOm-prOpErtY: 1; }',
+			message: messages.rejected('--cUstOm-prOpErtY'),
+		},
+		{
+			code:
+				'a { --custom-property: pink; { &:hover { --custom-property: orange; --custom-property: black; } } }',
+			description: 'spec nested',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code:
+				'a { --custom-property: pink; @media { --custom-property: orange; --custom-property: black; } }',
+			description: 'nested',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code:
+				'@media { --custom-property: orange; .foo { --custom-property: black; --custom-property: white; } }',
+			description: 'nested',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code:
+				'a { --custom-property: pink; @media { --custom-property: orange; &::before { --custom-property: black; --custom-property: white; } } }',
+			description: 'double nested',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code:
+				'a { --custom-property: pink; @media { --custom-property: orange; .foo { --custom-property: black; --custom-property: white; } } }',
+			description: 'double nested again',
+			message: messages.rejected('--custom-property'),
+		},
+	],
+});
+
+testRule({
+	ruleName,
+	config: [true],
+	skipBasicChecks: true,
+	syntax: 'html',
+
+	accept: [
+		{
+			code: '<style>a { --custom-property: pink; }</style>',
+		},
+		{
+			code: '<a style="--custom-property: pink;"></a>',
+		},
+		{
+			code:
+				'<style>a { --custom-property: pink; }</style><style>a { --custom-property: pink; }</style>',
+		},
+		{
+			code: '<a style="--custom-property: pink;"></a><a style="--custom-property: pink;"></a>',
+		},
+		{
+			code:
+				'<a style="--custom-property: pink; --cUstOm-prOpErtY: pink;"></a><a style="--custom-property: pink;"></a>',
+		},
+	],
+
+	reject: [
+		{
+			code: '<a style="--custom-property: pink; --custom-property: orange"></a>',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code:
+				'<style>p { color: pink; --custom-property: orange; --custom-property: white; }</style>',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code: '<a style="--custom-property: orange; color: pink; --custom-property: white;"></a>',
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code:
+				'<a style="--cUstOm-prOpErtY: orange; color: pink; --custom-property: white; --cUstOm-prOpErtY: black;"></a>',
+			message: messages.rejected('--cUstOm-prOpErtY'),
+		},
+	],
+});
+
+testRule({
+	ruleName,
+	config: [true],
+	skipBasicChecks: true,
+	syntax: 'css-in-js',
+
+	accept: [
+		{
+			code:
+				"import styled from 'react-emotion'\nexport default styled.div` --custom-property: pink; `;",
+		},
+		{
+			code:
+				"import styled from 'react-emotion'\nexport default styled.div` --custom-property: pink; --cUstOm-prOpErtY: pink; `;",
+		},
+	],
+	reject: [
+		{
+			code:
+				"import styled from 'styled-components';\nexport default styled.div` --custom-property: pink; --custom-property: orange; `;",
+			message: messages.rejected('--custom-property'),
+		},
+		{
+			code:
+				"import styled from 'react-emotion'\nexport default styled.div` --custom-property: pink; --custom-property: orange; `;",
+			message: messages.rejected('--custom-property'),
+		},
+	],
+});

lib/rules/declaration-block-no-duplicate-custom-properties/index.js

@@ -0,0 +1,61 @@
+// @ts-nocheck
+
+'use strict';
+
+const eachDeclarationBlock = require('../../utils/eachDeclarationBlock');
+const isCustomProperty = require('../../utils/isCustomProperty');
+const isStandardSyntaxProperty = require('../../utils/isStandardSyntaxProperty');
+const report = require('../../utils/report');
+const ruleMessages = require('../../utils/ruleMessages');
+const validateOptions = require('../../utils/validateOptions');
+
+const ruleName = 'declaration-block-no-duplicate-custom-properties';
+
+const messages = ruleMessages(ruleName, {
+	rejected: (property) => `Unexpected duplicate "${property}"`,
+});
+
+function rule(on) {
+	return (root, result) => {
+		const validOptions = validateOptions(result, ruleName, { actual: on });
+
+		if (!validOptions) {
+			return;
+		}
+
+		eachDeclarationBlock(root, (eachDecl) => {
+			const decls = new Set();
+
+			eachDecl((decl) => {
+				const prop = decl.prop;
+
+				if (!isStandardSyntaxProperty(prop)) {
+					return;
+				}
+
+				if (!isCustomProperty(prop)) {
+					return;
+				}
+
+				const isDuplicate = decls.has(prop);
+
+				if (isDuplicate) {
+					report({
+						message: messages.rejected(prop),
+						node: decl,
+						result,
+						ruleName,
+					});
+
+					return;
+				}
+
+				decls.add(prop);
+			});
+		});
+	};
+}
+
+rule.ruleName = ruleName;
+rule.messages = messages;
+module.exports = rule;

lib/rules/index.js

@@ -72,6 +72,9 @@ const rules = {
 	'custom-property-pattern': importLazy(() => require('./custom-property-pattern'))(),
 	'declaration-bang-space-after': importLazy(() => require('./declaration-bang-space-after'))(),
 	'declaration-bang-space-before': importLazy(() => require('./declaration-bang-space-before'))(),
+	'declaration-block-no-duplicate-custom-properties': importLazy(() =>
+		require('./declaration-block-no-duplicate-custom-properties'),
+	)(),
 	'declaration-block-no-duplicate-properties': importLazy(() =>
 		require('./declaration-block-no-duplicate-properties'),
 	)(),