feat: add no-unmatchable-selectors rule

README.md

@@ -76,6 +76,7 @@ export default defineConfig([
 | [`no-invalid-at-rules`](./docs/rules/no-invalid-at-rules.md)                         | Disallow invalid at-rules                             |       yes       |
 | [`no-invalid-named-grid-areas`](./docs/rules/no-invalid-named-grid-areas.md)         | Disallow invalid named grid areas                     |       yes       |
 | [`no-invalid-properties`](./docs/rules/no-invalid-properties.md)                     | Disallow invalid properties                           |       yes       |
+| [`no-unmatchable-selectors`](./docs/rules/no-unmatchable-selectors.md)               | Disallow unmatchable selectors                        |       yes       |
 | [`prefer-logical-properties`](./docs/rules/prefer-logical-properties.md)             | Enforce the use of logical properties                 |       no        |
 | [`relative-font-units`](./docs/rules/relative-font-units.md)                         | Enforce the use of relative font units                |       no        |
 | [`selector-complexity`](./docs/rules/selector-complexity.md)                         | Disallow and limit CSS selectors                      |       no        |

docs/rules/no-unmatchable-selectors.md

@@ -0,0 +1,55 @@
+# no-unmatchable-selectors
+
+Disallow unmatchable selectors.
+
+## Background
+
+An unmatchable selector is one that can never match any element in any document. These are effectively dead code and usually indicate mistakes.
+
+For example:
+
+- `a:nth-child(0)` — the `An+B` formula never produces a positive position (≥ 1).
+- `a:nth-child(-n)` — a negative step with no offset never yields a positive position.
+
+## Rule Details
+
+This rule reports selectors that can never match any element.
+
+It currently checks:
+
+- `:nth-*()` pseudo-classes whose `An+B` formulas cannot produce a positive position (≥ 1).
+
+Examples of **incorrect** code:
+
+<!-- prettier-ignore -->
+```css
+/* eslint css/no-unmatchable-selectors: "error" */
+
+a:nth-child(0) {}
+a:nth-child(-n) {}
+a:nth-last-child(0 of .active) {}
+a:nth-of-type(0n) {}
+a:nth-last-of-type(0n+0) {}
+```
+
+Examples of **correct** code:
+
+<!-- prettier-ignore -->
+```css
+/* eslint css/no-unmatchable-selectors: "error" */
+
+a:nth-child(1) {}
+a:nth-child(even) {}
+a:nth-child(odd) {}
+a:nth-last-child(1 of .active) {}
+a:nth-of-type(1n) {}
+a:nth-last-of-type(1n+0) {}
+```
+
+## When Not to Use It
+
+If you intentionally use selectors that can never match (for example, as temporary placeholders during development), then you can safely disable this rule.
+
+## Prior Art
+
+- [`selector-anb-no-unmatchable`](https://stylelint.io/user-guide/rules/selector-anb-no-unmatchable/)

src/rules/no-unmatchable-selectors.js

@@ -0,0 +1,61 @@
+/**
+ * @fileoverview Rule to disallow unmatchable selectors.
+ * @author TKDev7
+ */
+
+//-----------------------------------------------------------------------------
+// Type Definitions
+//-----------------------------------------------------------------------------
+
+/**
+ * @import { CSSRuleDefinition } from "../types.js"
+ * @typedef {"unmatchableSelector"} NoUnmatchableSelectorsMessageIds
+ * @typedef {CSSRuleDefinition<{ RuleOptions: [], MessageIds: NoUnmatchableSelectorsMessageIds }>} NoUnmatchableSelectorsRuleDefinition
+ */
+
+//-----------------------------------------------------------------------------
+// Rule Definition
+//-----------------------------------------------------------------------------
+
+/** @type {NoUnmatchableSelectorsRuleDefinition} */
+export default {
+	meta: {
+		type: "problem",
+
+		docs: {
+			description: "Disallow unmatchable selectors",
+			recommended: true,
+			url: "https://github.com/eslint/css/blob/main/docs/rules/no-unmatchable-selectors.md",
+		},
+
+		messages: {
+			unmatchableSelector:
+				"Unexpected unmatchable selector '{{selector}}'.",
+		},
+	},
+
+	create(context) {
+		const { sourceCode } = context;
+
+		return {
+			AnPlusB(node) {
+				// Either node.a or node.b can be null; Number(null) === 0.
+				// This coercion is intentional so that omitted coefficients are treated as 0.
+				const a = Number(node.a);
+				const b = Number(node.b);
+
+				if (a <= 0 && b <= 0) {
+					const pseudo = sourceCode.getParent(
+						sourceCode.getParent(node),
+					);
+
+					context.report({
+						loc: pseudo.loc,
+						messageId: "unmatchableSelector",
+						data: { selector: sourceCode.getText(pseudo) },
+					});
+				}
+			},
+		};
+	},
+};

tests/rules/no-unmatchable-selectors.test.js

@@ -0,0 +1,264 @@
+/**
+ * @fileoverview Tests for no-unmatchable-selectors rule.
+ * @author TKDev7
+ */
+
+//------------------------------------------------------------------------------
+// Imports
+//------------------------------------------------------------------------------
+
+import rule from "../../src/rules/no-unmatchable-selectors.js";
+import css from "../../src/index.js";
+import { RuleTester } from "eslint";
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+const ruleTester = new RuleTester({
+	plugins: { css },
+	language: "css/css",
+});
+
+ruleTester.run("no-unmatchable-selectors", rule, {
+	valid: [
+		"li:nth-child(1) {}",
+		"li:nth-child(n) {}",
+		"li:nth-child(-n+2) {}",
+		"li:nth-child(-2n+1) {}",
+		"li:nth-child(0n+1) {}",
+		"li:nth-child(2n) {}",
+		"li:nth-child(2n+0) {}",
+		"li:nth-child(2n-0) {}",
+		"li:nth-child(2n+2) {}",
+		"li:nth-child(1 of a) {}",
+		"li:nth-last-child(1) {}",
+		"li:nth-of-type(1) {}",
+		"li:nth-last-of-type(1) {}",
+		"li:nth-child(odd) {}",
+		"li:nth-child(even) {}",
+	],
+	invalid: [
+		{
+			code: "li:nth-child(0) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 16,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(0n) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(0n)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 17,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(+0n) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(+0n)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 18,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(-0n) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(-0n)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 18,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(0n+0) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(0n+0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 19,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(0n-0) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(0n-0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 19,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(-0n-0) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(-0n-0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 20,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(0n-2) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(0n-2)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 19,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(-n) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(-n)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 17,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(-2n) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(-2n)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 18,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(-3n+0) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(-3n+0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 20,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(-1) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(-1)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 17,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(0 of a) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(0 of a)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 21,
+				},
+			],
+		},
+		{
+			code: "li:nth-last-child(0) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-last-child(0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 21,
+				},
+			],
+		},
+		{
+			code: "li:nth-of-type(0) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-of-type(0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 18,
+				},
+			],
+		},
+		{
+			code: "li:nth-last-of-type(0) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-last-of-type(0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 23,
+				},
+			],
+		},
+		{
+			code: "li:nth-child(0), li:nth-child(1) {}",
+			errors: [
+				{
+					messageId: "unmatchableSelector",
+					data: { selector: ":nth-child(0)" },
+					line: 1,
+					column: 3,
+					endLine: 1,
+					endColumn: 16,
+				},
+			],
+		},
+	],
+});