Add a scanner and parser for platform selectors.

test/backend/platform_selector/parser_test.dart

Index: test/backend/platform_selector/parser_test.dart
diff --git a/test/backend/platform_selector/parser_test.dart b/test/backend/platform_selector/parser_test.dart
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+// Copyright (c) 2015, 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.
+
+import 'package:unittest/unittest.dart';
+import 'package:unittest/src/backend/platform_selector/ast.dart';
+import 'package:unittest/src/backend/platform_selector/parser.dart';
+
+/// A matcher that asserts that a value is a [ConditionalNode].
+Matcher _isConditionalNode =
+    new isInstanceOf<ConditionalNode>("ConditionalNode");
+
+/// A matcher that asserts that a value is an [OrNode].
+Matcher _isOrNode = new isInstanceOf<OrNode>("OrNode");
+
+/// A matcher that asserts that a value is an [AndNode].
+Matcher _isAndNode = new isInstanceOf<AndNode>("AndNode");
+
+/// A matcher that asserts that a value is a [NotNode].
+Matcher _isNotNode = new isInstanceOf<NotNode>("NotNode");
+
+void main() {
+  group("parses a conditional expression", () {
+    test("with identifiers", () {
+      var node = _parse("  a ? b : c   ");
+      expect(node.toString(), equals("a ? b : c"));
+
+      expect(node.span.text, equals("a ? b : c"));
+      expect(node.span.start.offset, equals(2));
+      expect(node.span.end.offset, equals(11));
+    });
+
+    test("with nested ors", () {
+      // Should parse as "(a || b) ? (c || d) : (e || f)".
+      // Should not parse as "a || (b ? (c || d) : (e || f))".
+      // Should not parse as "((a || b) ? (c || d) : e) || f".
+      // Should not parse as "a || (b ? (c || d) : e) || f".
+      _expectToString("a || b ? c || d : e || f",
+          "a || b ? c || d : e || f");
+    });
+
+    test("with a conditional expression as branch 1", () {
+      // Should parse as "a ? (b ? c : d) : e".
+      var node = _parse("a ? b ? c : d : e");
+      expect(node, _isConditionalNode);
+      expect(node.condition, _isVar("a"));
+      expect(node.whenFalse, _isVar("e"));
+
+      expect(node.whenTrue, _isConditionalNode);
+      expect(node.whenTrue.condition, _isVar("b"));
+      expect(node.whenTrue.whenTrue, _isVar("c"));
+      expect(node.whenTrue.whenFalse, _isVar("d"));
+    });
+
+    test("with a conditional expression as branch 2", () {
+      // Should parse as "a ? b : (c ? d : e)".
+      // Should not parse as "(a ? b : c) ? d : e".
+      var node = _parse("a ? b : c ? d : e");
+      expect(node, _isConditionalNode);
+      expect(node.condition, _isVar("a"));
+      expect(node.whenTrue, _isVar("b"));
+
+      expect(node.whenFalse, _isConditionalNode);
+      expect(node.whenFalse.condition, _isVar("c"));
+      expect(node.whenFalse.whenTrue, _isVar("d"));
+      expect(node.whenFalse.whenFalse, _isVar("e"));
+    });
+
+    group("which must have", () {
+      test("an expression after the ?", () {
+        expect(() => _parse("a ?"), throwsFormatException);
+        expect(() => _parse("a ? && b"), throwsFormatException);
+      });
+
+      test("a :", () {
+        expect(() => _parse("a ? b"), throwsFormatException);
+        expect(() => _parse("a ? b && c"), throwsFormatException);
+      });
+
+      test("an expression after the :", () {
+        expect(() => _parse("a ? b :"), throwsFormatException);
+        expect(() => _parse("a ? b : && c"), throwsFormatException);
+      });
+    });
+  });
+
+  group("parses an or expression", () {
+    test("with identifiers", () {
+      var node = _parse("  a || b   ");
+      expect(node, _isOrNode);
+      expect(node.left, _isVar("a"));
+      expect(node.right, _isVar("b"));
+
+      expect(node.span.text, equals("a || b"));
+      expect(node.span.start.offset, equals(2));
+      expect(node.span.end.offset, equals(8));
+    });
+
+    test("with nested ands", () {
+      // Should parse as "(a && b) || (c && d)".
+      // Should not parse as "a && (b || c) && d".
+      var node = _parse("a && b || c && d");
+      expect(node, _isOrNode);
+
+      expect(node.left, _isAndNode);
+      expect(node.left.left, _isVar("a"));
+      expect(node.left.right, _isVar("b"));
+
+      expect(node.right, _isAndNode);
+      expect(node.right.left, _isVar("c"));
+      expect(node.right.right, _isVar("d"));
+    });
+
+    test("with trailing ors", () {
+      // Should parse as "a || (b || (c || d))", although it doesn't affect the
+      // semantics.
+      var node = _parse("a || b || c || d");
+
+      for (var variable in ["a", "b", "c"]) {
+        expect(node, _isOrNode);
+        expect(node.left, _isVar(variable));
+        node = node.right;
+      }
+      expect(node, _isVar("d"));
+    });
+
+    test("which must have an expression after the ||", () {
+      expect(() => _parse("a ||"), throwsFormatException);
+      expect(() => _parse("a || && b"), throwsFormatException);
+    });
+  });
+
+  group("parses an and expression", () {
+    test("with identifiers", () {
+      var node = _parse("  a && b   ");
+      expect(node, _isAndNode);
+      expect(node.left, _isVar("a"));
+      expect(node.right, _isVar("b"));
+
+      expect(node.span.text, equals("a && b"));
+      expect(node.span.start.offset, equals(2));
+      expect(node.span.end.offset, equals(8));
+    });
+
+    test("with nested nots", () {
+      // Should parse as "(!a) && (!b)", obviously.
+      // Should not parse as "!(a && (!b))".
+      var node = _parse("!a && !b");
+      expect(node, _isAndNode);
+
+      expect(node.left, _isNotNode);
+      expect(node.left.child, _isVar("a"));
+
+      expect(node.right, _isNotNode);
+      expect(node.right.child, _isVar("b"));
+    });
+
+    test("with trailing ands", () {
+      // Should parse as "a && (b && (c && d))", although it doesn't affect the
+      // semantics since .
+      var node = _parse("a && b && c && d");
+
+      for (var variable in ["a", "b", "c"]) {
+        expect(node, _isAndNode);
+        expect(node.left, _isVar(variable));
+        node = node.right;
+      }
+      expect(node, _isVar("d"));
+    });
+
+    test("which must have an expression after the &&", () {
+      expect(() => _parse("a &&"), throwsFormatException);
+      expect(() => _parse("a && && b"), throwsFormatException);
+    });
+  });
+
+  group("parses a not expression", () {
+    test("with an identifier", () {
+      var node = _parse("  ! a    ");
+      expect(node, _isNotNode);
+      expect(node.child, _isVar("a"));
+
+      expect(node.span.text, equals("! a"));
+      expect(node.span.start.offset, equals(2));
+      expect(node.span.end.offset, equals(5));
+    });
+
+    test("with a parenthesized expression", () {
+      var node = _parse("!(a || b)");
+      expect(node, _isNotNode);
+
+      expect(node.child, _isOrNode);
+      expect(node.child.left, _isVar("a"));
+      expect(node.child.right, _isVar("b"));
+    });
+
+    test("with a nested not", () {
+      var node = _parse("!!a");
+      expect(node, _isNotNode);
+      expect(node.child, _isNotNode);
+      expect(node.child.child, _isVar("a"));
+    });
+
+    test("which must have an expression after the !", () {
+      expect(() => _parse("!"), throwsFormatException);
+      expect(() => _parse("! && a"), throwsFormatException);
+    });
+  });
+
+  group("parses a parenthesized expression", () {
+    test("with an identifier", () {
+      var node = _parse("(a)");
+      expect(node, _isVar("a"));
+    });
+
+    test("controls precedence", () {
+      // Without parentheses, this would parse as "(a || b) ? c : d".
+      var node = _parse("a || (b ? c : d)");
+
+      expect(node, _isOrNode);
+      expect(node.left, _isVar("a"));
+
+      expect(node.right, _isConditionalNode);
+      expect(node.right.condition, _isVar("b"));
+      expect(node.right.whenTrue, _isVar("c"));
+      expect(node.right.whenFalse, _isVar("d"));
+    });
+
+    group("which must have", () {
+      test("an expression within the ()", () {
+        expect(() => _parse("()"), throwsFormatException);
+        expect(() => _parse("( && a )"), throwsFormatException);
+      });
+
+      test("a matching )", () {
+        expect(() => _parse("( a"), throwsFormatException);
+      });
+    });
+  });
+
+  group("disallows", () {
+    test("an empty selector", () {
+      expect(() => _parse(""), throwsFormatException);
+    });
+
+    test("too many expressions", () {
+      expect(() => _parse("a b"), throwsFormatException);
+    });
+  });
+}
+
+/// Parses [selector] and returns its root node.
+Node _parse(String selector) => new Parser(selector).parse();
+
+/// A matcher that asserts that a value is a [VariableNode] with the given
+/// [name].
+Matcher _isVar(String name) => predicate(
+    (value) => value is VariableNode && value.name == name,
+    'is a variable named "$name"');
+
+void _expectToString(String selector, [String result]) {
+  if (result == null) result = selector;
+  expect(_toString(selector), equals(result),
+      reason: 'Expected toString of "$selector" to be "$result".');
+}
+
+String _toString(String selector) => new Parser(selector).parse().toString();