Fix small problems with precedence of cascades.

frog/tests/leg_only/src/CascadePrecedenceTest.dart

+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+
+class A {
+  int value;
+  A(this.value);
+  void set(int value) { this.value = value; }
+  int get() => value;
+  int operator[](int index) => value + index;
+  void operator[]=(int index, int newValue) { value += -index + newValue; }
+  void test(int expected) {
+    Expect.equals(expected, value);
+  }
+  Function limp(int n) {
+    if (n == 0) return set;
+    return () => limp(n - 1);
+  }
+  A get self() => this;
+  A operator+(A other) {
+    this.value += other.value;
+    return this;
+  }
+}
+
+class Box {
+  A value;
+  Box(this.value);
+  A operator[](int pos) => value;
+  void operator[]=(int pos, A a) { value = a; }
+  A get x() => value;
+  void set x(A a) { value = a; }
+}
+
+// Subset of grammar being tested.
+//
+// expression:
+//       assignableExpression assignmentOperator expression
+//     | conditionalExpression cascadeSection*
+//     ;
+// expressionWithoutCascade:
+//       assignableExpression assignmentOperator expressionWithoutCascade
+//     | conditionalExpression
+//     ;
+// expressionList:
+//       expression (',' expression)*
+//     ;
+// assignableExpression:
+//       primary (arguments* assignableSelector)+
+//     | super assignableSelector
+//     | identifier
+//     ;
+// conditionalExpression:
+//     logicalOrExpression ('?' expressionWithoutCascade ':' expressionWithoutCascade)?
+//     ;
+// primary:
+//       thisExpression
+//     | super assignableSelector
+//     | functionExpression
+//     | literal
+//     | identifier
+//     | newExpression
+//     | constObjectExpression
+//     | '(' expression ')'
+//     ;
+// assignableSelector:
+//       '[' expression ']'
+//     | '.' identifier
+//     ;
+//
+// In words:
+//  An assignableExpression is either a variable or something ending in
+//  [expression] or .identifier.
+
+main() {
+  A a = new A(42);
+  A original = a;
+  A b = new A(87);
+  fa() => a;
+  Box box = new Box(a);
+  // Different expressions on the left-hand side of '..'.
+  //  conditionalExpression >> postfixExpression > primary selector*
+  Expect.equals(a, a..set(37)..get());
+  a.test(37);
+  Expect.equals(a, fa()..set(42)..get());
+  a.test(42);
+  Expect.equals(a, box.x..set(37)..get());
+  a.test(37);
+  // '..' binds to 'b + a', i.e., to the 'b' object, not to 'a'.
+  Expect.equals(b, b + a..test(124)..set(117)..get());
+  b.test(117);
+  a.test(37);
+
+  // expression :: conditionalExpression cascadeSection
+  // and conditionalExpression ends in expressionWithoutCascade.
+  // I.e., '..' binds to the entire condition expression, not to 'b'.
+  (a.value == 37) ? a : b..set(42);
+  a.test(42);
+
+  // This binds .. to 'a', not 'c=a', and performs assignment after reading
+  // c.get().
+  A c = new A(21);
+  c = a..set(c.get());  // FAILING.
+  Expect.equals(a, c);
+  Expect.equals(original, a);
+  a.test(21);  // Fails as 42 if above is parsed as (c = a)..set(c.get()).
+
+  // Should be parsed as (box..x = (c = a))..x.test(21).
+  c = null;
+  box..x = c = a..x.test(21);
+  c.test(21);
+  // Other variants
+  c = null;
+  box..x = c = (a..test(21))..x.test(21);
+  c.test(21);
+
+  c = null;
+  box..x = (c = a..test(21))..x.test(21);
+  c.test(21);
+
+  // Should work the same:
+  (a..set(42))..test(42);
+  a..set(21)..test(21);
+
+  c = null;
+  Box originalBox = box;
+  // Should parse as:
+  // box = (box..x = (a.value == 21 ? b : c)..x.test(117));
+  box = box..x = a.value == 21 ? b : c..x.test(117);
+  Expect.equals(originalBox, box);
+  Expect.equals(box.value, b);
+
+  // New cascades are allowed inside an expressionWithoutCascade if properly
+  // delimited.
+  box..x = (a..set(42)..test(42))..x.test(42);
+}