add number-literal-case rule - fixes #55

docs/rules/number-literal-case.md

@@ -0,0 +1,27 @@
+# Enforce a lowercase literal identifier and an uppercase value
+
+Enforces a convention in defining number literals where the literal identifier is written in lowercase and the value in uppercase.
+
+
+## Fail
+
+```js
+const foo = 0XFF;
+const foo = 0xff;
+const foo = 0Xff;
+
+const foo = 0B11;
+
+const foo = 0O10;
+```
+
+
+## Pass
+
+```js
+const foo = 0xFF;
+
+const foo = 0b11;
+
+const foo = 0o10;
+```

index.js

@@ -18,7 +18,8 @@ module.exports = {
 				'unicorn/filename-case': ['error', {case: 'kebabCase'}],
 				'unicorn/no-abusive-eslint-disable': 'error',
 				'unicorn/no-process-exit': 'error',
-				'unicorn/throw-new-error': 'error'
+				'unicorn/throw-new-error': 'error',
+				'unicorn/number-literal-case': 'error'
 			}
 		}
 	}

readme.md

@@ -38,7 +38,8 @@ Configure it in `package.json`.
 			"unicorn/filename-case": ["error", {"case": "kebabCase"}],
 			"unicorn/no-abusive-eslint-disable": "error",
 			"unicorn/no-process-exit": "error",
-			"unicorn/throw-new-error": "error"
+			"unicorn/throw-new-error": "error",
+			"unicorn/number-literal-case": "error"
 		}
 	}
 }
@@ -53,6 +54,7 @@ Configure it in `package.json`.
 - [no-abusive-eslint-disable](docs/rules/no-abusive-eslint-disable.md) - Enforce specifying rules to disable in `eslint-disable` comments.
 - [no-process-exit](docs/rules/no-process-exit.md) - Disallow `process.exit()`.
 - [throw-new-error](docs/rules/throw-new-error.md) - Require `new` when throwing an error. *(fixable)*
+- [number-literal-case](docs/rules/number-literal-case.md) - Enforce a lowercase literal identifier and an uppercase value. *(fixable)*
 
 
 ## Recommended config

rules/number-literal-case.js

@@ -0,0 +1,41 @@
+'use strict';
+const fix = value => {
+	if (!/^0[a-zA-Z]/.test(value)) {
+		return value;
+	}
+
+	const indicator = value[1].toLowerCase();
+	const val = value.substring(2).toUpperCase();
+
+	return `0${indicator}${val}`;
+};
+
+const create = context => {
+	return {
+		Literal: node => {
+			const value = node.raw;
+			const fixedValue = fix(value);
+
+			if (value !== fixedValue) {
+				context.report({
+					node,
+					message: 'Invalid number literal casing',
+					fix: fixer => fixer.replaceText(node, fixedValue)
+				});
+			}
+		}
+	};
+};
+
+module.exports = {
+	meta: {
+		meta: {
+			docs: {
+				description: 'Enforce a lowercase literal identifier and an uppercase value',
+				recommended: 'error'
+			}
+		},
+		fixable: 'code'
+	},
+	create
+};

test/number-literal-case.js

@@ -0,0 +1,75 @@
+import test from 'ava';
+import avaRuleTester from 'eslint-ava-rule-tester';
+import rule from '../rules/number-literal-case';
+
+const ruleTester = avaRuleTester(test, {
+	env: {
+		es6: true
+	},
+	parserOptions: {
+		sourceType: 'module'
+	}
+});
+
+const error = {
+	ruleId: 'number-literal-case',
+	message: 'Invalid number literal casing'
+};
+
+ruleTester.run('number-literal-case', rule, {
+	valid: [
+		'const foo = 0xFF',
+		'const foo = 0b11',
+		'const foo = 0o10',
+		`const foo = '0Xff'`
+	],
+	invalid: [
+		{
+			code: 'const foo = 0XFF',
+			errors: [error],
+			output: 'const foo = 0xFF'
+		},
+		{
+			code: 'const foo = 0xff',
+			errors: [error],
+			output: 'const foo = 0xFF'
+		},
+		{
+			code: 'const foo = 0Xff',
+			errors: [error],
+			output: 'const foo = 0xFF'
+		},
+		{
+			code: 'const foo = 0Xff',
+			errors: [error],
+			output: 'const foo = 0xFF'
+		},
+		{
+			code: 'const foo = 0B11',
+			errors: [error],
+			output: 'const foo = 0b11'
+		},
+		{
+			code: 'const foo = 0O10',
+			errors: [error],
+			output: 'const foo = 0o10'
+		},
+		{
+			code: `
+				const foo = 255;
+
+				if (foo === 0xff) {
+					console.log('invalid');
+				}
+			`,
+			errors: [error],
+			output: `
+				const foo = 255;
+
+				if (foo === 0xFF) {
+					console.log('invalid');
+				}
+			`
+		}
+	]
+});