feat(eslint-plugin): Add a new blank-line-declaration-usage rule that lints against a missing empty line between variable declaration and its usage

Author: kresimir-coko

projects/eslint-plugin/configs/general.js

@@ -93,6 +93,7 @@ const config = {
 		'@liferay/aui/no-node': 'error',
 		'@liferay/aui/no-object': 'error',
 		'@liferay/aui/no-one': 'error',
+		'@liferay/blank-line-declaration-usage': 'error',
 		'@liferay/destructure-requires': 'error',
 		'@liferay/empty-line-between-elements': 'error',
 		'@liferay/expect-assert': 'error',

projects/eslint-plugin/rules/general/index.js

@@ -6,6 +6,7 @@
 module.exports = {
 	'array-is-array': require('./lib/rules/array-is-array'),
 	'destructure-requires': require('./lib/rules/destructure-requires'),
+	'blank-line-declaration-usage': require('./lib/rules/blank-line-declaration-usage'),
 	'empty-line-between-elements': require('./lib/rules/empty-line-between-elements'),
 	'expect-assert': require('./lib/rules/expect-assert'),
 	'group-imports': require('./lib/rules/group-imports'),

projects/eslint-plugin/rules/general/lib/rules/blank-line-declaration-usage.js

@@ -0,0 +1,72 @@
+/**
+ * SPDX-FileCopyrightText: © 2017 Liferay, Inc. <https://liferay.com>
+ * SPDX-License-Identifier: MIT
+ */
+
+const message =
+	'Expected an empty line between variable declaration and usage.';
+
+module.exports = {
+	create(context) {
+		const sourceCode = context.getSourceCode();
+
+		return {
+			VariableDeclaration(node) {
+				if (
+					node.parent.type === 'ForStatement' ||
+					node.parent.type === 'ForInStatement' ||
+					node.parent.type === 'ForOfStatement' ||
+					node.parent.type === 'WhileStatement'
+				) {
+					return;
+				}
+
+				const varsDeclaredOnLine = context.getDeclaredVariables(node);
+
+				const declarationLine =
+					varsDeclaredOnLine[0].identifiers[0].loc.start.line;
+
+				varsDeclaredOnLine.forEach((reference) => {
+					const varReference = reference.references[1];
+
+					if (varReference === undefined) {
+						return;
+					}
+
+					const referenceLine =
+						varReference.identifier.loc.start.line;
+
+					if (
+						sourceCode.lines
+							.slice(declarationLine, referenceLine - 1)
+							.indexOf('') === -1
+					) {
+						context.report({
+							fix: (fixer) => {
+								const declarationEndLine = node.loc.end.line;
+
+								if (referenceLine === declarationEndLine + 1) {
+									return fixer.insertTextAfter(node, '\n');
+								}
+							},
+							message,
+							node: reference.references[1].identifier,
+						});
+					}
+				});
+			},
+		};
+	},
+
+	meta: {
+		docs: {
+			category: 'Best Practices',
+			description: message,
+			recommended: false,
+			url: 'https://github.com/liferay/eslint-config-liferay/issues/139',
+		},
+		fixable: 'code',
+		schema: [],
+		type: 'problem',
+	},
+};

projects/eslint-plugin/rules/general/tests/lib/rules/blank-line-declaration-usage.js

@@ -0,0 +1,243 @@
+/**
+ * SPDX-FileCopyrightText: © 2017 Liferay, Inc. <https://liferay.com>
+ * SPDX-License-Identifier: MIT
+ */
+
+const MultiTester = require('../../../../../scripts/MultiTester');
+const rule = require('../../../lib/rules/blank-line-declaration-usage');
+
+const parserOptions = {
+	parserOptions: {
+		ecmaVersion: 6,
+	},
+};
+
+const message =
+	'Expected an empty line between variable declaration and usage.';
+
+const ruleTester = new MultiTester(parserOptions);
+
+ruleTester.run('blank-line-declaration-usage', rule, {
+	invalid: [
+		{
+			code: `
+				const test = 'test';
+				const testLength = test.length;
+			`,
+			errors: [
+				{
+					message,
+					type: 'Identifier',
+				},
+			],
+			output: `
+				const test = 'test';
+
+				const testLength = test.length;
+			`,
+		},
+		{
+			code: `
+				const obj = {
+					foo: 'bar',
+					bar: 'foo',
+					life: 'ray',
+				}
+				Object.keys(obj)
+			`,
+			errors: [
+				{
+					message,
+					type: 'Identifier',
+				},
+			],
+			output: `
+				const obj = {
+					foo: 'bar',
+					bar: 'foo',
+					life: 'ray',
+				}
+
+				Object.keys(obj)
+			`,
+		},
+		{
+			code: `
+				function updateData() {
+					const obj = {
+						foo: 'bar',
+						bar: 'foo',
+						life: 'ray',
+					}
+
+					const ids = Object.keys(obj).length
+						? 'superLongStringSoThatItForcesTheLineToBeWrapped'
+						: 'justASimpleString';
+					ids.length;
+				}
+			`,
+			errors: [
+				{
+					message,
+					type: 'Identifier',
+				},
+			],
+			output: `
+				function updateData() {
+					const obj = {
+						foo: 'bar',
+						bar: 'foo',
+						life: 'ray',
+					}
+
+					const ids = Object.keys(obj).length
+						? 'superLongStringSoThatItForcesTheLineToBeWrapped'
+						: 'justASimpleString';
+
+					ids.length;
+				}
+			`,
+		},
+		{
+			code: `
+				const obj = {
+					foo: 'bar',
+					bar: 'foo',
+					life: 'ray',
+				}
+
+				const {foo} = obj;
+				const length = foo.length;
+			`,
+			errors: [
+				{
+					message,
+					type: 'Identifier',
+				},
+			],
+			output: `
+				const obj = {
+					foo: 'bar',
+					bar: 'foo',
+					life: 'ray',
+				}
+
+				const {foo} = obj;
+
+				const length = foo.length;
+			`,
+		},
+		{
+			code: `
+				const {foo, bar, life} = obj;
+				const length = life.length;
+			`,
+			errors: [
+				{
+					message,
+					type: 'Identifier',
+				},
+			],
+			output: `
+				const {foo, bar, life} = obj;
+
+				const length = life.length;
+			`,
+		},
+		{
+			code: `
+				const filePath = context.getFilename();
+				const filename = path.basename(something, filePath);
+			`,
+			errors: [
+				{
+					message,
+					type: 'Identifier',
+				},
+			],
+			output: `
+				const filePath = context.getFilename();
+
+				const filename = path.basename(something, filePath);
+			`,
+		},
+		{
+			code: `
+				for (const file of files) {
+					const contents = readFileAsync(file, 'utf8');
+					const length = contents.length;
+				}
+			`,
+			errors: [
+				{
+					message,
+					type: 'Identifier',
+				},
+			],
+			output: `
+				for (const file of files) {
+					const contents = readFileAsync(file, 'utf8');
+
+					const length = contents.length;
+				}
+			`,
+		},
+		{
+			code: `
+				const cbSpy = sinon.spy();
+				prototype.rows = [cbSpy];
+			`,
+			errors: [
+				{
+					message,
+					type: 'Identifier',
+				},
+			],
+			output: `
+				const cbSpy = sinon.spy();
+
+				prototype.rows = [cbSpy];
+			`,
+		},
+	],
+	valid: [
+		{
+			code: `
+				const test = 'test';
+
+				const testLength = test.length;
+			`,
+		},
+		{
+			code: `
+				const obj = {
+					foo: 'bar',
+					bar: 'foo',
+					life: 'ray',
+				}
+
+				Object.keys(obj).map(key => {});
+			`,
+		},
+		{
+			code: `
+				const obj = {
+					foo: 'bar',
+					bar: 'foo',
+					life: 'ray',
+				}
+
+				const {foo} = obj;
+
+				const length = foo.length;
+			`,
+		},
+		{
+			code: `
+				for (const file of files) {
+					const contents = readFileAsync(file, 'utf8');
+				}
+			`,
+		},
+	],
+});