[RegExp] Add support for arbitrary repetition ranges.

Author: renggli

lib/src/regexp/node.dart

@@ -159,29 +159,50 @@ class QuantificationNode extends Node {
 
   @override
   Nfa toNfa() {
-    final start = NfaState(isEnd: false);
-    final end = NfaState(isEnd: true);
-    final childNfa = child.toNfa();
     if (min == 0 && max == null) {
+      final start = NfaState(isEnd: false);
+      final end = NfaState(isEnd: true);
+      final childNfa = child.toNfa();
       start.epsilons.add(end);
       start.epsilons.add(childNfa.start);
       childNfa.end.epsilons.add(end);
       childNfa.end.epsilons.add(childNfa.start);
       childNfa.end.isEnd = false;
+      return Nfa(start: start, end: end);
     } else if (min == 0 && max == 1) {
+      final start = NfaState(isEnd: false);
+      final end = NfaState(isEnd: true);
+      final childNfa = child.toNfa();
       start.epsilons.add(end);
       start.epsilons.add(childNfa.start);
       childNfa.end.epsilons.add(end);
       childNfa.end.isEnd = false;
-    } else if (min == 1 && max == null) {
-      start.epsilons.add(childNfa.start);
-      childNfa.end.epsilons.add(end);
-      childNfa.end.epsilons.add(childNfa.start);
-      childNfa.end.isEnd = false;
+      return Nfa(start: start, end: end);
+    }
+    final nfas = <Nfa>[];
+    for (var i = 0; i < min; i++) {
+      nfas.add(child.toNfa());
+    }
+    if (max == null) {
+      nfas.add(QuantificationNode(child, 0, null).toNfa());
     } else {
-      throw UnsupportedError(toString());
+      for (var i = 0; i < max! - min; i++) {
+        nfas.add(QuantificationNode(child, 0, 1).toNfa());
+      }
     }
-    return Nfa(start: start, end: end);
+    if (nfas.isEmpty) {
+      final start = NfaState(isEnd: false);
+      final end = NfaState(isEnd: true);
+      start.epsilons.add(end);
+      return Nfa(start: start, end: end);
+    }
+    for (var i = 0; i < nfas.length - 1; i++) {
+      final current = nfas[i];
+      final next = nfas[i + 1];
+      current.end.epsilons.add(next.start);
+      current.end.isEnd = false;
+    }
+    return Nfa(start: nfas.first.start, end: nfas.last.end);
   }
 
   @override

test/regexp_test.dart

@@ -136,7 +136,6 @@ void main() {
       });
     }
     test('unsupported', () {
-      expect(() => Node.fromString(r'a{2,}').toNfa(), throwsUnsupportedError);
       expect(() => Node.fromString(r'a&b').toNfa(), throwsUnsupportedError);
       expect(() => Node.fromString(r'!a').toNfa(), throwsUnsupportedError);
     });
@@ -377,6 +376,34 @@ const tests = [
     Expect('aababab', false),
     Expect('aabbbbb', false),
   ]),
+  // Arbitrary ranges
+  Test(r'a{3}', [
+    Expect('', false),
+    Expect('a', false),
+    Expect('aa', false),
+    Expect('aaa', true),
+    Expect('aaaa', false),
+  ]),
+  Test(r'a{2,}', [
+    Expect('', false),
+    Expect('a', false),
+    Expect('aa', true),
+    Expect('aaa', true),
+    Expect('aaaa', true),
+  ]),
+  Test(r'a{1,3}', [
+    Expect('', false),
+    Expect('a', true),
+    Expect('aa', true),
+    Expect('aaa', true),
+    Expect('aaaa', false),
+  ]),
+  Test(r'a{,2}', [
+    Expect('', true),
+    Expect('a', true),
+    Expect('aa', true),
+    Expect('aaa', false),
+  ]),
   // https://github.com/xysun/regex/blob/master/testing.py
   Test(r'(ab|a)(bc|c)', [Expect('abc', true), Expect('acb', false)]),
   Test(r'(ab)c|abc', [Expect('abc', true), Expect('ab', false)]),