Add a scanner and parser for platform selectors.

test/backend/platform_selector/scanner_test.dart

+// 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/scanner.dart';
+import 'package:unittest/src/backend/platform_selector/token.dart';
+
+void main() {
+  group("peek()", () {
+    test("returns the next token without consuming it", () {
+      var scanner = new Scanner("( )");
+      expect(scanner.peek().type, equals(TokenType.leftParen));
+      expect(scanner.peek().type, equals(TokenType.leftParen));
+      expect(scanner.peek().type, equals(TokenType.leftParen));
+    });
+
+    test("returns an end-of-file token at the end of a file", () {
+      var scanner = new Scanner("( )");
+      scanner.next();
+      scanner.next();
+
+      var token = scanner.peek();
+      expect(token.type, equals(TokenType.endOfFile));
+      expect(token.span.start.offset, equals(3));
+      expect(token.span.end.offset, equals(3));
+    });
+
+    test("throws a StateError if peek() is called after end-of-file was "
+        "consumed", () {
+      var scanner = new Scanner("( )");
+      scanner.next();
+      scanner.next();
+      scanner.next();
+      expect(() => scanner.peek(), throwsStateError);
+    });
+  });
+
+  group("next()", () {
+    test("next() consumes and returns the next token", () {
+      var scanner = new Scanner("( )");
+      expect(scanner.next().type, equals(TokenType.leftParen));
+      expect(scanner.peek().type, equals(TokenType.rightParen));
+      expect(scanner.next().type, equals(TokenType.rightParen));
+    });
+
+    test("returns an end-of-file token at the end of a file", () {

[Bob Nystrom, 2015/03/11 20:05:53]

This is a dupe of line 18.

[nweiz, 2015/03/12 19:48:58]

It calls [scanner.next] instead of [scanner.peek].

[Bob Nystrom, 2015/03/12 20:37:21]

My reading comprehension grade: F.

+      var scanner = new Scanner("( )");
+      scanner.next();
+      scanner.next();
+
+      var token = scanner.next();
+      expect(token.type, equals(TokenType.endOfFile));
+      expect(token.span.start.offset, equals(3));
+      expect(token.span.end.offset, equals(3));
+    });
+
+    test("throws a StateError if peek() is called after end-of-file was "

[Bob Nystrom, 2015/03/11 20:05:53]

Ditto.

[nweiz, 2015/03/12 19:48:58]

Ditto.

+        "consumed", () {
+      var scanner = new Scanner("( )");
+      scanner.next();
+      scanner.next();
+      scanner.next();
+      expect(() => scanner.next(), throwsStateError);
+    });
+  });
+
+  group("scans a simple token:", () {
+    test("left paren", () => _expectSimpleScan("(", TokenType.leftParen));
+    test("right paren", () => _expectSimpleScan(")", TokenType.rightParen));
+    test("or", () => _expectSimpleScan("||", TokenType.or));
+    test("and", () => _expectSimpleScan("&&", TokenType.and));
+    test("not", () => _expectSimpleScan("!", TokenType.not));
+    test("question mark", () => _expectSimpleScan("?", TokenType.questionMark));
+    test("colon", () => _expectSimpleScan(":", TokenType.colon));
+  });
+
+  group("scans an identifier that", () {
+    test("is simple", () {
+      var token = _scan("   foo  ");
+      expect(token.name, equals("foo"));
+      expect(token.span.text, equals("foo"));
+      expect(token.span.start.offset, equals(3));
+      expect(token.span.end.offset, equals(6));
+    });
+
+    test("is a single character", () {
+      var token = _scan("f");
+      expect(token.name, equals("f"));
+    });
+
+    test("has a leading underscore", () {
+      var token = _scan("_foo");
+      expect(token.name, equals("_foo"));
+    });
+
+    test("has a leading dash", () {
+      var token = _scan("-foo");
+      expect(token.name, equals("-foo"));
+    });
+
+    test("contains an underscore", () {
+      var token = _scan("foo_bar");
+      expect(token.name, equals("foo_bar"));
+    });
+
+    test("contains a dash", () {
+      var token = _scan("foo-bar");
+      expect(token.name, equals("foo-bar"));
+    });
+
+    test("is capitalized", () {
+      var token = _scan("FOO");
+      expect(token.name, equals("FOO"));
+    });
+
+    test("contains numbers", () {
+      var token = _scan("foo123");
+      expect(token.name, equals("foo123"));
+    });
+  });
+
+  test("scans an empty selector", () {
+    expect(_scan("").type, equals(TokenType.endOfFile));
+  });
+
+  test("scans multiple tokens", () {
+    var scanner = new Scanner("(foo && bar)");
+
+    var token = scanner.next();
+    expect(token.type, equals(TokenType.leftParen));
+    expect(token.span.start.offset, equals(0));
+    expect(token.span.end.offset, equals(1));
+
+    token = scanner.next();
+    expect(token.type, equals(TokenType.identifier));
+    expect(token.name, equals("foo"));
+    expect(token.span.start.offset, equals(1));
+    expect(token.span.end.offset, equals(4));
+
+    token = scanner.next();
+    expect(token.type, equals(TokenType.and));
+    expect(token.span.start.offset, equals(5));
+    expect(token.span.end.offset, equals(7));
+
+    token = scanner.next();
+    expect(token.type, equals(TokenType.identifier));
+    expect(token.name, equals("bar"));
+    expect(token.span.start.offset, equals(8));
+    expect(token.span.end.offset, equals(11));
+
+    token = scanner.next();
+    expect(token.type, equals(TokenType.rightParen));
+    expect(token.span.start.offset, equals(11));
+    expect(token.span.end.offset, equals(12));
+
+    token = scanner.next();
+    expect(token.type, equals(TokenType.endOfFile));
+    expect(token.span.start.offset, equals(12));
+    expect(token.span.end.offset, equals(12));
+  });
+
+  group("ignores", () {
+    test("a single-line comment", () {
+      var scanner = new Scanner("( // &&\n// ||\n)");
+      expect(scanner.next().type, equals(TokenType.leftParen));
+      expect(scanner.next().type, equals(TokenType.rightParen));
+      expect(scanner.next().type, equals(TokenType.endOfFile));
+    });
+
+    test("a single-line comment without a trailing newline", () {
+      var scanner = new Scanner("( // &&");
+      expect(scanner.next().type, equals(TokenType.leftParen));
+      expect(scanner.next().type, equals(TokenType.endOfFile));
+    });
+
+    test("a multi-line comment", () {
+      var scanner = new Scanner("( /* && * /\n|| */\n)");
+      expect(scanner.next().type, equals(TokenType.leftParen));
+      expect(scanner.next().type, equals(TokenType.rightParen));
+      expect(scanner.next().type, equals(TokenType.endOfFile));
+    });
+
+    test("a multi-line nested comment", () {
+      var scanner = new Scanner("(/* && /* ? /* || */ : */ ! */)");
+      expect(scanner.next().type, equals(TokenType.leftParen));
+      expect(scanner.next().type, equals(TokenType.rightParen));
+      expect(scanner.next().type, equals(TokenType.endOfFile));
+    });
+
+    test("Dart's notion of whitespace", () {
+      var scanner = new Scanner("( \t \n)");
+      expect(scanner.next().type, equals(TokenType.leftParen));
+      expect(scanner.next().type, equals(TokenType.rightParen));
+      expect(scanner.next().type, equals(TokenType.endOfFile));
+    });
+  });
+
+  group("disallows", () {
+    test("a single |", () {
+      expect(() => _scan("|"), throwsFormatException);
+    });
+
+    test('"| |"', () {
+      expect(() => _scan("| |"), throwsFormatException);
+    });
+
+    test("a single &", () {
+      expect(() => _scan("&"), throwsFormatException);
+    });
+
+    test('"& &"', () {
+      expect(() => _scan("& &"), throwsFormatException);
+    });
+
+    test("an unknown operator", () {
+      expect(() => _scan("=="), throwsFormatException);
+    });
+
+    test("unicode", () {
+      expect(() => _scan("öh"), throwsFormatException);
+    });
+
+    test("an unclosed multi-line comment", () {
+      expect(() => _scan("/*"), throwsFormatException);
+    });
+
+    test("an unopened multi-line comment", () {
+      expect(() => _scan("*/"), throwsFormatException);
+    });
+  });
+}
+
+/// Asserts that the first token scanned from [selector] has type [type],
+/// and that that token's span is exactly [selector].
+void _expectSimpleScan(String selector, TokenType type) {
+  // Complicate the selector to test that the span covers it correctly.
+  var token = _scan("   $selector  ");
+  expect(token.type, equals(type));
+  expect(token.span.text, equals(selector));
+  expect(token.span.start.offset, equals(3));
+  expect(token.span.end.offset, equals(3 + selector.length));
+}
+
+/// Scans a single token from [selector].
+Token _scan(String selector) => new Scanner(selector).next();