fix: Add support period-separated layer names in use-layers rule

docs/rules/use-layers.md

@@ -91,7 +91,7 @@ When `allowUnnamedLayers` is set to `true`, the following code is **correct**:
 
 #### `layerNamePattern`
 
-The `layerNamePattern` is a regular expression string that allows you to validate the name of layers and prevent misspellings.
+The `layerNamePattern` is a regular expression string that allows you to validate the name of layers and prevent misspellings. This option supports period-separated layer names (e.g., `foo.bar`) as defined in [CSS Cascade and Inheritance Level 5](https://drafts.csswg.org/css-cascade-5/#layer-names).
 
 Here's an example of **incorrect** code:
 
@@ -106,8 +106,21 @@ Here's an example of **incorrect** code:
 		color: red;
 	}
 }
+
+/* unknown period-separated layer name */
+@layer theme.custom {
+	a {
+		color: red;
+	}
+}
 ```
 
+Each part of a period-separated layer name is validated individually against the pattern. For example, with `layerNamePattern: "^(reset|theme|base)$"`:
+
+- `theme.base` is valid (both parts match the pattern)
+- `theme.custom` is invalid (`custom` doesn't match the pattern)
+- `other.base` is invalid (`other` doesn't match the pattern)
+
 #### `requireImportLayers: false`
 
 When `requireImportLayers` is set to `false`, the following code is **correct**:

src/rules/use-layers.js

@@ -89,16 +89,39 @@ export default {
 					return;
 				}
 
-				if (!layerNameRegex.test(node.name)) {
-					context.report({
-						loc: node.loc,
-						messageId: "layerNameMismatch",
-						data: {
-							name: node.name,
-							pattern: options.layerNamePattern,
-						},
-					});
-				}
+				const parts = node.name.split(".");
+				let currentPos = 0;
+
+				parts.forEach((part, index) => {
+					if (!layerNameRegex.test(part)) {
+						const startColumn = node.loc.start.column + currentPos;
+						const endColumn = startColumn + part.length;
+
+						context.report({
+							loc: {
+								start: {
+									line: node.loc.start.line,
+									column: startColumn,
+								},
+								end: {
+									line: node.loc.start.line,
+									column: endColumn,
+								},
+							},
+							messageId: "layerNameMismatch",
+							data: {
+								name: part,
+								pattern: options.layerNamePattern,
+							},
+						});
+					}
+
+					currentPos += part.length;
+					// add 1 to account for the . symbol
+					if (index < parts.length - 1) {
+						currentPos += 1;
+					}
+				});
 			},
 
 			"Atrule[name=layer]"(node) {

tests/rules/use-layers.test.js

@@ -57,6 +57,22 @@ ruleTester.run("use-layers", rule, {
 			code: "@import 'foo.css';",
 			options: [{ requireImportLayers: false }],
 		},
+		{
+			code: "@layer foo.bar { a { color: red; } }",
+			options: [{ layerNamePattern: "^(foo|bar)$" }],
+		},
+		{
+			code: "@layer foo.bar.baz { a { color: red; } }",
+			options: [{ layerNamePattern: "^(foo|bar|baz)$" }],
+		},
+		{
+			code: "@import 'foo.css' layer(foo.bar);",
+			options: [{ layerNamePattern: "^(foo|bar)$" }],
+		},
+		{
+			code: "@layer foo, bar.baz, baz.qux;",
+			options: [{ layerNamePattern: "^(foo|bar|baz|qux)$" }],
+		},
 	],
 	invalid: [
 		{
@@ -263,5 +279,134 @@ ruleTester.run("use-layers", rule, {
 				},
 			],
 		},
+		{
+			code: "@layer foo.bar { a { color: red; } }",
+			options: [{ layerNamePattern: "bar" }],
+			errors: [
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "foo",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 8,
+					endLine: 1,
+					endColumn: 11,
+				},
+			],
+		},
+		{
+			code: "@layer foo.baz { a { color: red; } }",
+			options: [{ layerNamePattern: "bar" }],
+			errors: [
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "foo",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 8,
+					endLine: 1,
+					endColumn: 11,
+				},
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "baz",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 12,
+					endLine: 1,
+					endColumn: 15,
+				},
+			],
+		},
+		{
+			code: "@layer foo.bar, baz.qux { a { color: red; } }",
+			options: [{ layerNamePattern: "bar" }],
+			errors: [
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "foo",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 8,
+					endLine: 1,
+					endColumn: 11,
+				},
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "baz",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 17,
+					endLine: 1,
+					endColumn: 20,
+				},
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "qux",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 21,
+					endLine: 1,
+					endColumn: 24,
+				},
+			],
+		},
+		{
+			code: "@import 'style.css' layer(foo.bar);",
+			options: [{ layerNamePattern: "bar" }],
+			errors: [
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "foo",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 27,
+					endLine: 1,
+					endColumn: 30,
+				},
+			],
+		},
+		{
+			code: "@import 'style.css' layer(foo.baz);",
+			options: [{ layerNamePattern: "bar" }],
+			errors: [
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "foo",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 27,
+					endLine: 1,
+					endColumn: 30,
+				},
+				{
+					messageId: "layerNameMismatch",
+					data: {
+						name: "baz",
+						pattern: "bar",
+					},
+					line: 1,
+					column: 31,
+					endLine: 1,
+					endColumn: 34,
+				},
+			],
+		},
 	],
 });