Add ignore: [single-declaration] to declaration-block-trailing-semicolon

lib/rules/declaration-block-trailing-semicolon/README.md

@@ -88,3 +88,38 @@ a { color: pink }
 ```css
 a { background: orange; color: pink }
 ```
+
+## Optional secondary options
+
+### `ignore: ["single-declaration"]`
+
+#### `"single-declaration"`
+
+The following patterns are _not_ considered violations:
+
+<!-- prettier-ignore -->
+```css
+foo { property: value }
+```
+
+<!-- prettier-ignore -->
+```css
+foo { property: value; }
+```
+
+<!-- prettier-ignore -->
+```css
+@keyframes name { from { property: 0 } to { property: 1; } }
+```
+
+With `"always"`:
+
+The following pattern is _still_ considered a violation:
+
+<!-- prettier-ignore -->
+```css
+foo {
+  property: value;
+  bar: qux
+}
+```

lib/rules/declaration-block-trailing-semicolon/__tests__/index.js

@@ -62,6 +62,58 @@ testRule({
 	],
 });
 
+testRule({
+	ruleName,
+	config: ['always', { ignore: 'single-declaration' }],
+	fix: true,
+
+	accept: [
+		{
+			code: 'foo { property: value }',
+			description: 'single declaration without trailing semicolon',
+		},
+		{
+			code: 'foo { property: value; }',
+			description: 'single declaration with trailing semicolon',
+		},
+		{
+			code: '@keyframes name { from { property: 0 } to { property: 1; } }',
+			description: 'inconsistent case (with and without)',
+		},
+	],
+
+	reject: [
+		{
+			code: 'a { background: orange; color: pink }',
+			fixed: 'a { background: orange; color: pink; }',
+			description: 'multi declaration block without trailing semicolon',
+			message: messages.expected,
+			line: 1,
+			column: 35,
+		},
+	],
+});
+
+testRule({
+	ruleName,
+	config: ['never', { ignore: ['single-declaration'] }],
+
+	accept: [
+		{
+			code: 'foo { property: value }',
+			description: 'single declaration without trailing semicolon',
+		},
+		{
+			code: 'foo { property: value; }',
+			description: 'single declaration with trailing semicolon',
+		},
+		{
+			code: '@keyframes name { from { property: 0 } to { property: 1; } }',
+			description: 'inconsistent case (with and without)',
+		},
+	],
+});
+
 testRule({
 	ruleName,
 	config: ['never'],

lib/rules/declaration-block-trailing-semicolon/index.js

@@ -3,6 +3,7 @@
 'use strict';
 
 const hasBlock = require('../../utils/hasBlock');
+const optionsMatches = require('../../utils/optionsMatches');
 const report = require('../../utils/report');
 const ruleMessages = require('../../utils/ruleMessages');
 const validateOptions = require('../../utils/validateOptions');
@@ -14,12 +15,23 @@ const messages = ruleMessages(ruleName, {
 	rejected: 'Unexpected trailing semicolon',
 });
 
-function rule(expectation, _, context) {
+function rule(expectation, options, context) {
 	return (root, result) => {
-		const validOptions = validateOptions(result, ruleName, {
-			actual: expectation,
-			possible: ['always', 'never'],
-		});
+		const validOptions = validateOptions(
+			result,
+			ruleName,
+			{
+				actual: expectation,
+				possible: ['always', 'never'],
+			},
+			{
+				actual: options,
+				possible: {
+					ignore: ['single-declaration'],
+				},
+				optional: true,
+			},
+		);
 
 		if (!validOptions) {
 			return;
@@ -54,10 +66,16 @@ function rule(expectation, _, context) {
 		});
 
 		function checkLastNode(node) {
+			const hasSemicolon = node.parent.raws.semicolon;
+			const ignoreSingleDeclaration = optionsMatches(options, 'ignore', 'single-declaration');
 			let message;
 
+			if (ignoreSingleDeclaration && node.parent.first === node) {
+				return;
+			}
+
 			if (expectation === 'always') {
-				if (node.parent.raws.semicolon) {
+				if (hasSemicolon) {
 					return;
 				}
 
@@ -75,7 +93,7 @@ function rule(expectation, _, context) {
 
 				message = messages.expected;
 			} else if (expectation === 'never') {
-				if (!node.parent.raws.semicolon) {
+				if (!hasSemicolon) {
 					return;
 				}