add some necessary exceptions to strict_variables = true handling

src/twig.expression.js

@@ -847,7 +847,25 @@ module.exports = function (Twig) {
                 return Twig.expression.resolveAsync.call(state, context[token.value], context)
                     .then(value => {
                         if (state.template.options.strictVariables && value === undefined) {
-                            throw new Twig.Error('Variable "' + token.value + '" does not exist.');
+                            let skipException = false;
+                            if (token.peek) {
+                                const {peek} = token;
+                                if (peek.type === Twig.expression.type.filter && peek.value === 'default') {
+                                    skipException = true;
+                                }
+
+                                if (peek.type === Twig.expression.type.operator.binary && peek.value === '??') {
+                                    skipException = true;
+                                }
+
+                                if (peek.type === Twig.expression.type.test && peek.filter === 'defined') {
+                                    skipException = true;
+                                }
+                            }
+
+                            if (!skipException) {
+                                throw new Twig.Error('Variable "' + token.value + '" does not exist.');
+                            }
                         }
 
                         stack.push(value);
@@ -1255,6 +1273,7 @@ module.exports = function (Twig) {
 
         while (tokens.length > 0) {
             token = tokens.shift();
+            token.peek = tokens[0];
             tokenTemplate = Twig.expression.handler[token.type];
 
             Twig.log.trace('Twig.expression.compile: ', 'Compiling ', token);

test/test.options.js

@@ -82,4 +82,36 @@ describe('Twig.js Optional Functionality ->', function () {
             }
         });
     });
+
+    describe('should not throw an error when `strict_variables` set to `true`', function () {
+        const filter = twig({
+            rethrow: true,
+            strict_variables: true,
+            data: '{{ test|default }}'
+        });
+
+        const nullcoalescing = twig({
+            rethrow: true,
+            strict_variables: true,
+            data: '{{ test ?? \'test\' }}'
+        });
+
+        const test = twig({
+            rethrow: true,
+            strict_variables: true,
+            data: '{% if test is defined %}{% endif %}'
+        });
+
+        it('For undefined variables with default filter', function () {
+            filter.render();
+        });
+
+        it('For undefined variables with ?? operator', function () {
+            nullcoalescing.render();
+        });
+
+        it('For undefined variables with defined test', function () {
+            test.render();
+        });
+    });
 });