requireTemplateStrings: should not report string to binary

For `{"allExcept": ["stringConcatenation"]}`

Fixes #2050

Author: markelog

lib/rules/require-template-strings.js

@@ -93,15 +93,26 @@ module.exports.prototype = {
             );
         }
 
+        var i = 0;
         file.iterateNodesByType('BinaryExpression', function(node) {
             if (node.operator !== '+') {
                 return;
             }
 
-            var leftIsString = typeof node.left.value === 'string' ||
-                node.left.type === 'TemplateLiteral';
-            var rightIsString = typeof node.right.value === 'string' ||
-                node.right.type === 'TemplateLiteral';
+            var leftIsString = node.left;
+            var rightIsString = node.right;
+
+            // Left side could also be binary expression (See gh-2050),
+            // but not the right one
+            while (leftIsString.type === 'BinaryExpression') {
+                leftIsString = leftIsString.left;
+            }
+
+            leftIsString = typeof leftIsString.value === 'string' ||
+                leftIsString.type === 'TemplateLiteral'
+
+            rightIsString = typeof rightIsString.value === 'string' ||
+                rightIsString.type === 'TemplateLiteral';
 
             if (allowStringConcatenation && leftIsString && rightIsString) {
                 return;

test/specs/rules/require-template-strings.js

@@ -153,6 +153,18 @@ describe('rules/require-template-strings', function() {
         it('should not report the use of string concatenation with two template strings', function() {
             expect(checker.checkString('`a` + `a`')).to.have.no.errors();
         });
+
+        it('should not report string with binary concatination', function() {
+            expect(checker.checkString('"a" + "b" + "c";')).to.have.no.errors();
+        });
+
+        it('should not report string with binary concatination for three operands', function() {
+            expect(checker.checkString('"a" + "b" + "c";')).to.have.no.errors();
+        });
+
+        it('should not report string with binary concatination for four operands', function() {
+            expect(checker.checkString('"a" + "b" + "c" + "d";')).to.have.no.errors();
+        });
     });
 
     describe('invalid options', function() {