Add assignment expressions. (#13)

Add assignment expressions.

Assignment expressions can be either normal or null-aware
(using ??=). This commit also does some cleanup regarding
Tokens, moving all Token literals to a shared file.

lib/code_builder.dart

@@ -30,11 +30,11 @@ library code_builder;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/token.dart';
-import 'package:analyzer/src/dart/ast/token.dart';
 import 'package:dart_style/dart_style.dart';
 import 'package:meta/meta.dart';
 
 import 'src/analyzer_patch.dart';
+import 'src/tokens.dart';
 
 part 'src/builders/annotation_builder.dart';
 part 'src/builders/class_builder.dart';
@@ -56,13 +56,10 @@ final DartFormatter _dartfmt = new DartFormatter();
 @visibleForTesting
 String dartfmt(String source) => _dartfmt.format(source);
 
-Identifier _stringIdentifier(String s) {
-  return new SimpleIdentifier(new StringToken(TokenType.STRING, s, 0));
-}
+SimpleIdentifier _stringIdentifier(String s) =>
+    new SimpleIdentifier(stringToken(s));
 
-Literal _stringLiteral(String s) {
-  return new SimpleStringLiteral(new StringToken(TokenType.STRING, s, 0), s);
-}
+Literal _stringLiteral(String s) => new SimpleStringLiteral(stringToken(s), s);
 
 /// Base class for building and emitting a Dart language [AstNode].
 abstract class CodeBuilder<A extends AstNode> {

lib/src/builders/class_builder.dart

@@ -6,11 +6,6 @@ part of code_builder;
 
 /// Builds a [ClassDeclaration] AST.
 class ClassBuilder implements CodeBuilder<ClassDeclaration> {
-  static Token _abstract = new KeywordToken(Keyword.ABSTRACT, 0);
-  static Token _extends = new KeywordToken(Keyword.EXTENDS, 0);
-  static Token _implements = new KeywordToken(Keyword.IMPLEMENTS, 0);
-  static Token _with = new KeywordToken(Keyword.WITH, 0);
-
   final String _name;
   final bool _isAbstract;
   final TypeBuilder _extend;
@@ -85,18 +80,18 @@ class ClassBuilder implements CodeBuilder<ClassDeclaration> {
   ClassDeclaration toAst([Scope scope = const Scope.identity()]) {
     var astNode = _emptyClassDeclaration()..name = _stringIdentifier(_name);
     if (_isAbstract) {
-      astNode.abstractKeyword = _abstract;
+      astNode.abstractKeyword = $abstract;
     }
     if (_extend != null) {
-      astNode.extendsClause = new ExtendsClause(_extends, _extend.toAst(scope));
+      astNode.extendsClause = new ExtendsClause($extends, _extend.toAst(scope));
     }
     if (_implement.isNotEmpty) {
-      astNode.implementsClause = new ImplementsClause(_implements,
+      astNode.implementsClause = new ImplementsClause($implements,
           _implement.map/*<TypeName>*/((i) => i.toAst(scope)).toList());
     }
     if (_mixin.isNotEmpty) {
       astNode.withClause = new WithClause(
-          _with, _mixin.map/*<TypeName>*/((i) => i.toAst(scope)).toList());
+          $with, _mixin.map/*<TypeName>*/((i) => i.toAst(scope)).toList());
     }
     astNode
       ..metadata.addAll(_metadata.map/*<Annotation>*/((a) => a.toAst(scope)));

lib/src/builders/constructor_builder.dart

@@ -8,9 +8,6 @@ part of code_builder;
 ///
 /// Similar to [MethodBuilder] but with constructor-only features.
 class ConstructorBuilder implements CodeBuilder<ConstructorDeclaration> {
-  static final Token _const = new KeywordToken(Keyword.CONST, 0);
-  static final Token _this = new KeywordToken(Keyword.THIS, 0);
-
   final bool _isConstant;
   final String _name;
   final List<ParameterBuilder> _parameters = <ParameterBuilder>[];
@@ -43,7 +40,7 @@ class ConstructorBuilder implements CodeBuilder<ConstructorDeclaration> {
       null,
       null,
       null,
-      _isConstant ? _const : null,
+      _isConstant ? $const : null,
       null,
       null,
       _name != null ? _stringIdentifier(_name) : null,
@@ -53,7 +50,7 @@ class ConstructorBuilder implements CodeBuilder<ConstructorDeclaration> {
       null,
       null,
       null,
-      new EmptyFunctionBody(MethodBuilder._semicolon),
+      new EmptyFunctionBody($semicolon),
     );
     return astNode;
   }

lib/src/builders/expression_builder.dart

@@ -14,15 +14,8 @@ const literalNull = const _LiteralNull();
 /// Represents an expression value of `true`.
 const literalTrue = const LiteralBool(true);
 
-// Returns wrapped as a [ExpressionFunctionBody] AST.
-final Token _closeP = new Token(TokenType.CLOSE_PAREN, 0);
-
-// Returns wrapped as a [FunctionExpression] AST.
-final Token _openP = new Token(TokenType.OPEN_PAREN, 0);
-
-final Token _semicolon = new Token(TokenType.SEMICOLON, 0);
-
 // TODO(matanl): Make this part of the public API. See annotation_builder.dart.
+// Returns wrapped as a [ExpressionFunctionBody] AST.
 ExpressionFunctionBody _asFunctionBody(
   CodeBuilder<Expression> expression,
   Scope scope,
@@ -31,22 +24,23 @@ ExpressionFunctionBody _asFunctionBody(
     null,
     null,
     expression.toAst(scope),
-    _semicolon,
+    $semicolon,
   );
 }
 
+// Returns wrapped as a [FunctionExpression] AST.
 FunctionExpression _asFunctionExpression(
   CodeBuilder<Expression> expression,
   Scope scope,
 ) {
   return new FunctionExpression(
     null,
     new FormalParameterList(
-      _openP,
+      $openParen,
       const [],
       null,
       null,
-      _closeP,
+      $closeParen,
     ),
     _asFunctionBody(expression, scope),
   );
@@ -108,6 +102,15 @@ abstract class ExpressionBuilder implements CodeBuilder<Expression> {
     );
   }
 
+  /// Assign [left] to [right].
+  ///
+  /// If [nullAware] is true, the assignment uses the `??=` operator.
+  factory ExpressionBuilder.assignment(
+      String left, CodeBuilder<Expression> right,
+      {bool nullAware: false}) {
+    return new _AssignmentExpression(left, right, nullAware: nullAware);
+  }
+
   const ExpressionBuilder._();
 
   /// Return a new [ExpressionBuilder] invoking the result of this expression.
@@ -136,10 +139,8 @@ abstract class ExpressionBuilder implements CodeBuilder<Expression> {
 
 /// Creates a new literal `bool` value.
 class LiteralBool extends _LiteralExpression<BooleanLiteral> {
-  static final BooleanLiteral _true =
-      new BooleanLiteral(new KeywordToken(Keyword.TRUE, 0), true);
-  static final BooleanLiteral _false =
-      new BooleanLiteral(new KeywordToken(Keyword.FALSE, 0), false);
+  static final BooleanLiteral _true = new BooleanLiteral($true, true);
+  static final BooleanLiteral _false = new BooleanLiteral($false, false);
 
   final bool _value;
 
@@ -159,7 +160,7 @@ class LiteralInt extends _LiteralExpression<IntegerLiteral> {
 
   @override
   IntegerLiteral toAst([_]) => new IntegerLiteral(
-        new StringToken(TokenType.INT, '$_value', 0),
+        intToken(_value),
         _value,
       );
 }
@@ -173,18 +174,12 @@ class LiteralString extends _LiteralExpression<StringLiteral> {
 
   @override
   StringLiteral toAst([_]) => new SimpleStringLiteral(
-        new StringToken(
-          TokenType.STRING,
-          "'$_value'",
-          0,
-        ),
+        stringToken("'$_value'"),
         _value,
       );
 }
 
 class _InvokeExpression extends ExpressionBuilder {
-  static final Token _colon = new Token(TokenType.COLON, 0);
-
   final String _importFrom;
   final ExpressionBuilder _target;
   final String _name;
@@ -231,18 +226,18 @@ class _InvokeExpression extends ExpressionBuilder {
     // TODO(matanl): Move to TypeBuilder.newInstance.
     if (_type != null) {
       return new InstanceCreationExpression(
-        new KeywordToken(Keyword.NEW, 0),
+        $new,
         new ConstructorName(
           _type.toAst(scope),
-          _name != null ? new Token(TokenType.PERIOD, 0) : null,
+          _name != null ? $period : null,
           _name != null ? _stringIdentifier(_name) : null,
         ),
         _getArgumentList(scope),
       );
     }
     return new MethodInvocation(
       _target?.toAst(scope),
-      _target != null ? new Token(TokenType.PERIOD, 0) : null,
+      _target != null ? $period : null,
       _stringIdentifier(_name),
       null,
       _getArgumentList(scope),
@@ -254,21 +249,46 @@ class _InvokeExpression extends ExpressionBuilder {
 
   ArgumentList _getArgumentList(Scope scope) {
     return new ArgumentList(
-      new Token(TokenType.OPEN_CURLY_BRACKET, 0),
+      $openCurly,
       _positionalArguments.map/*<Expression*/((p) => p.toAst(scope)).toList()
         ..addAll(_namedArguments.keys
             .map/*<Expression>*/((name) => new NamedExpression(
                   new Label(
                     _stringIdentifier(name),
-                    _colon,
+                    $colon,
                   ),
                   _namedArguments[name].toAst(scope),
                 ))),
-      new Token(TokenType.CLOSE_CURLY_BRACKET, 0),
+      $closeCurly,
     );
   }
 }
 
+class _AssignmentExpression extends ExpressionBuilder {
+  final String left;
+  final CodeBuilder<Expression> right;
+  final bool nullAware;
+
+  _AssignmentExpression(this.left, this.right, {this.nullAware: false})
+      : super._();
+
+  @override
+  ExpressionBuilder invokeSelf(String name,
+      {Iterable<CodeBuilder<Expression>> positional: const [],
+      Map<String, CodeBuilder<Expression>> named: const {}}) {
+    return _invokeSelfImpl(this, name, positional: positional, named: named);
+  }
+
+  @override
+  Expression toAst([Scope scope = const Scope.identity()]) {
+    return new AssignmentExpression(_stringIdentifier(left),
+        nullAware ? $nullAwareEquals : $equals, right.toAst(scope));
+  }
+
+  @override
+  StatementBuilder toStatement() => new _ExpressionStatementBuilder(this);
+}
+
 abstract class _LiteralExpression<A extends Literal>
     implements ExpressionBuilder, CodeBuilder<A> {
   const _LiteralExpression();
@@ -296,7 +316,7 @@ abstract class _LiteralExpression<A extends Literal>
 }
 
 class _LiteralNull extends _LiteralExpression<NullLiteral> {
-  static NullLiteral _null = new NullLiteral(new KeywordToken(Keyword.NULL, 0));
+  static final NullLiteral _null = new NullLiteral($null);
 
   const _LiteralNull();
 

lib/src/builders/field_builder.dart

@@ -10,13 +10,6 @@ part of code_builder;
 /// AST (for class members) via [toFieldAst] or a variable declaration (used
 /// both at the top-level and within methods) via [toVariablesAst].
 class FieldBuilder implements CodeBuilder<Declaration> {
-  static Token _equals = new Token(TokenType.EQ, 0);
-  static Token _semicolon = new Token(TokenType.SEMICOLON, 0);
-  static Token _static = new KeywordToken(Keyword.STATIC, 0);
-  static Token _final = new KeywordToken(Keyword.FINAL, 0);
-  static Token _const = new KeywordToken(Keyword.CONST, 0);
-  static Token _var = new KeywordToken(Keyword.VAR, 0);
-
   final bool _isConst;
   final bool _isFinal;
   final bool _isStatic;
@@ -84,7 +77,7 @@ class FieldBuilder implements CodeBuilder<Declaration> {
       new FieldDeclaration(
         null,
         null,
-        _isStatic ? _static : null,
+        _isStatic ? $static : null,
         toVariablesAst(scope),
         null,
       );
@@ -100,19 +93,19 @@ class FieldBuilder implements CodeBuilder<Declaration> {
         [
           new VariableDeclaration(
             _stringIdentifier(_name),
-            _initialize != null ? _equals : null,
+            _initialize != null ? $equals : null,
             _initialize?.toAst(scope),
           )
         ],
       );
 
   Token _getVariableKeyword() {
     if (_isFinal) {
-      return _final;
+      return $final;
     }
     if (_isConst) {
-      return _const;
+      return $const;
     }
-    return _type == null ? _var : null;
+    return _type == null ? $var : null;
   }
 }

lib/src/builders/file_builder.dart

@@ -92,8 +92,6 @@ class ImportBuilder implements CodeBuilder<ImportDirective> {
 
 /// Builds a standalone Dart library [CompilationUnit] AST.
 class LibraryBuilder extends FileBuilder {
-  static final Token _library = new KeywordToken(Keyword.LIBRARY, 0);
-
   final String _name;
   final Scope _scope;
 
@@ -128,7 +126,7 @@ class LibraryBuilder extends FileBuilder {
         new LibraryDirective(
           null,
           null,
-          _library,
+          $library,
           new LibraryIdentifier([_stringIdentifier(_name)]),
           null,
         ),
@@ -142,9 +140,6 @@ class LibraryBuilder extends FileBuilder {
 
 /// Builds a `part of` [CompilationUnit] AST for an existing Dart library.
 class PartBuilder extends FileBuilder {
-  static final Token _part = new KeywordToken(Keyword.PART, 0);
-  static final Token _of = new StringToken(TokenType.KEYWORD, 'of', 0);
-
   final String _name;
 
   /// Create a new `part of` source file.
@@ -158,8 +153,8 @@ class PartBuilder extends FileBuilder {
     originalAst.directives.add(new PartOfDirective(
       null,
       null,
-      _part,
-      _of,
+      $part,
+      $of,
       new LibraryIdentifier([_stringIdentifier(_name)]),
       null,
     ));