Optimize a{0,1} → a?

Author: Richienb

src/optimizer/transforms/__tests__/quantifier-range-to-symbol-transform-test.js

@@ -45,4 +45,11 @@ describe('quantifier range to symbol', () => {
     expect(re.toString()).toBe('/[a-z]{3}/');
   });
 
+  it('a{0,1} -> a?', () => {
+    const re = transform('/[a-z]{0,1}/', [
+      quantifierRangeToSymbol
+    ]);
+    expect(re.toString()).toBe('/[a-z]?/');
+  });
+
 });

src/optimizer/transforms/quantifier-range-to-symbol-transform.js

@@ -12,6 +12,7 @@
  * a{0,} -> a*
  * a{1,} -> a+
  * a{1} -> a
+ * a{0,1} -> a?
  *
  * NOTE: the following is automatically handled in the generator:
  *
@@ -33,6 +34,9 @@ module.exports = {
 
     // a{1} -> a
     rewriteExactOne(path);
+
+    // a{0,1} -> a?
+    rewriteZeroOne(path);
   }
 };
 
@@ -67,3 +71,14 @@ function rewriteExactOne(path) {
 
   path.parentPath.replace(path.parentPath.node.expression);
 }
+
+function rewriteZeroOne(path) {
+  const {node} = path;
+
+  if (node.from !== 0 || node.to !== 1) {
+    return;
+  }
+
+  node.kind = '?';
+  delete node.from;
+}