Cleanup more (?:) from patterns

src/xregexp.js

@@ -238,6 +238,21 @@ function getContextualTokenSeparator(match, scope, flags) {
         // No need to separate tokens if at the beginning or end of a group
         match.input[match.index - 1] === '(' ||
         match.input[match.index + match[0].length] === ')' ||
+
+        // No need to separate tokens if at the beginning of a non-capturing group or lookahead
+        //
+        // If `match.index - 3` is negative, the substring will be too short to match, so the test will fail.
+        // For example: '1234'.substr(-1, 3) === '4'
+        nativ.test.call(/\(\?[:=!]/, match.input.substr(match.index - 3, 3)) ||
+
+        // No need to separate tokens if before or after a `|`
+        match.input[match.index - 1] === '|' ||
+        match.input[match.index + match[0].length] === '|' ||
+
+        // No need to separate tokens if at the beginning or end of the pattern
+        match.index < 1 ||
+        match.index + match[0].length >= match.input.length ||
+
         // Avoid separating tokens when the following token is a quantifier
         isQuantifierNext(match.input, match.index + match[0].length, flags)
     ) {

tests/spec/s-xregexp.js

@@ -800,6 +800,34 @@ describe('XRegExp()', function() {
                 expect(XRegExp('(#\n.#\n)', 'x').source).toBe('(.)');
             });
 
+            it('should not add atom separator (?:) at the beginning or end of non-capturing groups in simple cases', function() {
+                expect(XRegExp('(?: . )', 'x').source).toBe('(?:.)');
+                expect(XRegExp('(?:#\n.#\n)', 'x').source).toBe('(?:.)');
+
+                expect(XRegExp(' (?: . )', 'x').source).toBe('(?:.)');
+                expect(XRegExp(' (?:#\n.#\n)', 'x').source).toBe('(?:.)');
+            });
+
+            it('should not add atom separator (?:) at the beginning or end of a lookahead in simple cases', function() {
+                expect(XRegExp('(?= . )', 'x').source).toBe('(?=.)');
+                expect(XRegExp('(?=#\n.#\n)', 'x').source).toBe('(?=.)');
+            });
+
+            it('should not add atom separator (?:) at the beginning or end of a negated lookahead in simple cases', function() {
+                expect(XRegExp('(?! . )', 'x').source).toBe('(?!.)');
+                expect(XRegExp('(?!#\n.#\n)', 'x').source).toBe('(?!.)');
+            });
+
+            it('should not add atom separator (?:) at the beginning or end of the pattern in simple cases', function() {
+                expect(XRegExp(' ( . ) ', 'x').source).toBe('(.)');
+                expect(XRegExp(' (#\n.#\n) ', 'x').source).toBe('(.)');
+            });
+
+            it('should not add atom separator (?:) around | in simple cases', function() {
+                expect(XRegExp('( a | b )', 'x').source).toBe('(a|b)');
+                expect(XRegExp('(#\na#\n|#\nb#\n)', 'x').source).toBe('(a|b)');
+            });
+
             it('should allow whitespace between ( and ? for special groups', function() {
                 expect(XRegExp('( ?:)', 'x').source).toBe('(?:)');
                 expect(XRegExp('( ?=)', 'x').source).toBe('(?=)');