New Rule: disallowSemicolons

Only allows semicolons at the beginning of a line

Fixes gh-712
Closes gh-732

README.md

@@ -3667,6 +3667,34 @@ Invalid:
  */
 ```
 
+### disallowSemicolons
+
+Disallows lines from ending in a semicolon.
+
+Type: `Boolean`
+
+Value: `true`
+
+#### Example
+
+```js
+"disallowSemicolons": true
+```
+
+##### Valid
+
+```js
+var a = 1
+;[b].forEach(c)
+```
+
+##### Invalid
+
+```js
+var a = 1;
+[b].forEach(c);
+```
+
 ### ~~validateJSDoc~~
 
 Please use the [JSCS-JSDoc](https://github.com/jscs-dev/jscs-jsdoc) plugin instead.

lib/config/configuration.js

@@ -595,6 +595,8 @@ Configuration.prototype.registerDefaultRules = function() {
     this.registerRule(require('../rules/disallow-capitalized-comments'));
 
     this.registerRule(require('../rules/require-line-break-after-variable-assignment'));
+
+    this.registerRule(require('../rules/disallow-semicolons'));
 };
 
 /**

lib/rules/disallow-semicolons.js

@@ -0,0 +1,30 @@
+var assert = require('assert');
+var tokenHelper = require('../token-helper');
+
+module.exports = function() {};
+
+module.exports.prototype = {
+    configure: function(disallowSemicolons) {
+        assert(
+            disallowSemicolons === true,
+            'disallowSemicolons option requires true value or should be removed'
+        );
+    },
+
+    getOptionName: function() {
+        return 'disallowSemicolons';
+    },
+
+    check: function(file, errors) {
+        file.getTokens()
+            .filter(function(token) {
+                return token.type === 'Punctuator' && token.value === ';';
+            })
+            .forEach(function(token) {
+                var nextToken = file.getNextToken(token);
+                if (!nextToken || nextToken.loc.end.line > token.loc.end.line) {
+                    errors.add('semicolons are disallowed at the end of a line.', token.loc.end);
+                }
+            });
+    }
+};

test/rules/disallow-semicolons.js

@@ -0,0 +1,36 @@
+var Checker = require('../../lib/checker');
+var assert = require('assert');
+
+describe('rules/disallow-semicolons', function() {
+    var checker;
+
+    beforeEach(function() {
+        checker = new Checker();
+        checker.registerDefaultRules();
+        checker.configure({ disallowSemicolons: true });
+    });
+
+    it('should not allow semicolons at end of line', function() {
+        assert(checker.checkString([
+            'var a = 1;',
+            'var b = 2;',
+            'function c() {}',
+            'd();'
+        ].join('\n')).getErrorCount() === 3);
+    });
+
+    it('should allow semicolons inline', function() {
+        assert(checker.checkString([
+            'for (var i = 0; i < l; i++) {',
+            'go()',
+            '}'
+        ].join('\n')).isEmpty());
+    });
+
+    it('should allow semicolons at start of line', function() {
+        assert(checker.checkString([
+            'var foo = function () {}',
+            ';[1, 2].forEach(foo)'
+        ].join('\n')).isEmpty());
+    });
+});