Allow no-process-exit to be used in process event handlers (fixes #32) (#44)

Author: jfmengels

docs/rules/no-process-exit.md

@@ -1,6 +1,6 @@
 # Disallow `process.exit()`
 
-This rule is an extension to ESLint's [`no-process-exit` rule](http://eslint.org/docs/rules/no-process-exit), that allows `process.exit()` to be called in files that start with a [hashbang](https://en.wikipedia.org/wiki/Shebang_(Unix)) → `#!/usr/bin/env node`.
+This rule is an extension to ESLint's [`no-process-exit` rule](http://eslint.org/docs/rules/no-process-exit), that allows `process.exit()` to be called in files that start with a [hashbang](https://en.wikipedia.org/wiki/Shebang_(Unix)) → `#!/usr/bin/env node`. It also allows `process.exit()` to be called in `process.on('<event>', func)` event handlers.
 
 
 ## Fail
@@ -16,3 +16,10 @@ process.exit(0);
 #!/usr/bin/env node
 process.exit(0);
 ```
+
+```js
+process.on('SIGINT', () => {
+    console.log('Got SIGINT');
+    process.exit(1);
+});
+```

rules/no-process-exit.js

@@ -6,15 +6,29 @@ module.exports = context => {
 		return {};
 	}
 
+	let processEventHandler = null;
+
 	return {
-		CallExpression: node => {
+		'CallExpression': node => {
 			const callee = node.callee;
 
-			if (callee.type === 'MemberExpression' && callee.object.name === 'process' && callee.property.name === 'exit') {
-				context.report({
-					node,
-					message: 'Only use `process.exit()` in CLI apps. Throw an error instead.'
-				});
+			if (callee.type === 'MemberExpression' && callee.object.name === 'process') {
+				if (callee.property.name === 'on') {
+					processEventHandler = node;
+					return;
+				}
+
+				if (callee.property.name === 'exit' && !processEventHandler) {
+					context.report({
+						node,
+						message: 'Only use `process.exit()` in CLI apps. Throw an error instead.'
+					});
+				}
+			}
+		},
+		'CallExpression:exit': node => {
+			if (node === processEventHandler) {
+				processEventHandler = null;
 			}
 		}
 	};

test/no-process-exit.js

@@ -8,14 +8,22 @@ const ruleTester = avaRuleTester(test, {
 	}
 });
 
-const errors = [{ruleId: 'no-process-exit'}];
+const errors = [{
+	ruleId: 'no-process-exit',
+	message: 'Only use `process.exit()` in CLI apps. Throw an error instead.'
+}];
 
 ruleTester.run('no-process-exit', rule, {
 	valid: [
 		'#!/usr/bin/env node\n\nprocess.exit();',
 		'Process.exit()',
 		'const x = process.exit;',
 		'x(process.exit)',
+		'process.on("SIGINT", function() { process.exit(1); })',
+		'process.on("SIGKILL", function() { process.exit(1); })',
+		'process.on("SIGINT", () => { process.exit(1); })',
+		'process.on("SIGINT", () => process.exit(1))',
+		'process.on("SIGINT", () => { if (true) { process.exit(1); } })',
 		''
 	],
 	invalid: [