Add support for library scoping

lib/code_builder.dart

@@ -73,14 +73,14 @@ abstract class _AbstractCodeBuilder<A extends AstNode> extends CodeBuilder<A> {
 /// **NOTE**: This currently (as of 0.2.0) has no effect. It is planned that
 /// the [FileBuilder] will be able to act as a scope 'resolver' and subtly
 /// rewrite the AST tree to use prefixing if required (or requested).
-abstract class RequiresImport<A extends AstNode> implements CodeBuilder<A> {
-  /// Imports that are required for this AST to work.
-  List<String> get requiredImports;
+abstract class ScopeAware<A extends AstNode> implements CodeBuilder<A> {
+  @override
+  A toAst() => toScopedAst(const Scope.identity());
 
   /// Creates a copy-safe [AstNode] representing the current builder state.
   ///
   /// Uses [scope] to output an AST re-written to use appropriate prefixes.
-  A toScopedAst(FileBuilder scope) => throw new UnimplementedError();
+  A toScopedAst(Scope scope) => throw new UnimplementedError();
 }
 
 // Creates a defensive copy of an AST node.

lib/src/builders/annotation_builder.dart

@@ -16,7 +16,7 @@ part of code_builder;
 ///   void destroyTheWorld() { ... }
 ///
 /// To create a `@DoNotUse('Blows up')` use [AnnotationBuilder.invoke].
-abstract class AnnotationBuilder implements RequiresImport<Annotation> {
+abstract class AnnotationBuilder implements ScopeAware<Annotation> {
   /// Create a new annotated `const` [constructor] invocation.
   ///
   /// May optionally specify an [importFrom] to auto-prefix the annotation _if_
@@ -46,7 +46,7 @@ abstract class AnnotationBuilder implements RequiresImport<Annotation> {
       [String importFrom]) = _ReferenceAnnotationBuilder;
 }
 
-class _ConstructorAnnotationBuilder extends RequiresImport<Annotation>
+class _ConstructorAnnotationBuilder extends ScopeAware<Annotation>
     implements AnnotationBuilder {
   final String _constructor;
   final ExpressionBuilder _expression;

lib/src/builders/file_builder.dart

@@ -28,6 +28,8 @@ abstract class FileBuilder extends _AbstractCodeBuilder<CompilationUnit> {
 class LibraryBuilder extends FileBuilder {
   static final Token _library = new KeywordToken(Keyword.LIBRARY, 0);
 
+  final Scope _scope;
+
   /// Create a new standalone Dart library, optionally with a [name].
   factory LibraryBuilder([String name]) {
     var astNode = _emptyCompilationUnit();
@@ -39,22 +41,49 @@ class LibraryBuilder extends FileBuilder {
           new LibraryIdentifier([_stringId(name)]),
           null,));
     }
-    return new LibraryBuilder._(astNode);
+    return new LibraryBuilder._(astNode, new Scope.dedupe());
   }
 
   /// Create a new standalone Dart library, optionally with a [name].
   ///
-  /// As references are added in the library that implements [RequiresImport]
+  /// As references are added in the library that implements [ScopeAware]
   /// they are re-written to avoid collisions and the imports are automatically
   /// included at the top with optional prefixes.
-  factory LibraryBuilder.autoScope({String name}) => new LibraryBuilder(name);
+  factory LibraryBuilder.scope({String name, Scope scope}) {
+    var astNode = _emptyCompilationUnit();
+    if (name != null) {
+      astNode.directives.add(new LibraryDirective(
+          null,
+          null,
+          _library,
+          new LibraryIdentifier([_stringId(name)]),
+          null,));
+    }
+    return new LibraryBuilder._(astNode, scope ?? new Scope());
+  }
 
-  LibraryBuilder._(CompilationUnit astNode) : super._(astNode);
+  LibraryBuilder._(CompilationUnit astNode, this._scope) : super._(astNode);
+
+  @override
+  void addDeclaration(CodeBuilder<Declaration> declaration) {
+    if (declaration is ScopeAware<Declaration>) {
+      _astNode.declarations.add(declaration.toScopedAst(_scope));
+    } else {
+      super.addDeclaration(declaration);
+    }
+  }
 
   /// Adds [directive]'s resulting AST to the source.
   void addDirective(CodeBuilder<Directive> directive) {
     _astNode.directives.add(directive.toAst());
   }
+
+  @override
+  CompilationUnit toAst() {
+    var originalAst = super.toAst();
+    originalAst.directives..addAll(_scope.getImports().map((i) => i.toAst()));
+    return originalAst;
+  }
 }
 
 /// Builds a `part of` [CompilationUnit] AST for an existing Dart library.

lib/src/builders/method_builder.dart

@@ -11,7 +11,9 @@ part of code_builder;
 /// the top level and within other methods) via [toFunctionAst].
 ///
 /// To return nothing (`void`), use [MethodBuilder.returnVoid].
-class MethodBuilder implements CodeBuilder<Declaration> {
+class MethodBuilder implements
+    CodeBuilder<Declaration>,
+    ScopeAware<Declaration> {
   static Token _abstract = new KeywordToken(Keyword.ABSTRACT, 0);
   static Token _semicolon = new Token(TokenType.SEMICOLON, 0);
   static Token _static = new KeywordToken(Keyword.STATIC, 0);
@@ -41,6 +43,9 @@ class MethodBuilder implements CodeBuilder<Declaration> {
 
   MethodBuilder._(this._name, this._returnType);
 
+  @override
+  List<String> get requiredImports => null;
+
   /// Lazily adds [annotation].
   ///
   /// When the method is emitted as an AST, [AnnotationBuilder.toAst] is used.
@@ -76,14 +81,14 @@ class MethodBuilder implements CodeBuilder<Declaration> {
   /// [toMethodAst].
   @override
   @visibleForTesting
-  Declaration toAst() => toFunctionAst();
+  Declaration toAst() => toScopedAst(const Scope.identity());
 
   /// Returns a copy-safe [FunctionDeclaration] AST representing current state.
-  FunctionDeclaration toFunctionAst() {
+  FunctionDeclaration toFunctionAst({Scope scope: const Scope.identity()}) {
     var functionAst = _emptyFunction()
       ..metadata.addAll(_annotations.map/*<Annotation>*/((a) => a.toAst()))
       ..name = _stringId(_name)
-      ..returnType = _returnType?.toAst();
+      ..returnType = _returnType?.toScopedAst(scope);
     if (_returnExpression != null) {
       functionAst.functionExpression = _returnExpression.toFunctionExpression();
     } else {
@@ -95,7 +100,7 @@ class MethodBuilder implements CodeBuilder<Declaration> {
     }
     if (_parameters.isNotEmpty) {
       functionAst.functionExpression.parameters.parameters
-          .addAll(_parameters.map/*<FormalParameter>*/((p) => p.toAst()));
+          .addAll(_parameters.map/*<FormalParameter>*/((p) => p.toScopedAst(scope)));
     }
     return functionAst;
   }
@@ -104,11 +109,12 @@ class MethodBuilder implements CodeBuilder<Declaration> {
   MethodDeclaration toMethodAst({
     bool static: false,
     bool canBeAbstract: false,
+    Scope scope: const Scope.identity(),
   }) {
     var methodAst = _emptyMethod()
       ..metadata.addAll(_annotations.map/*<Annotation>*/((a) => a.toAst()))
       ..name = _stringId(_name)
-      ..returnType = _returnType?.toAst();
+      ..returnType = _returnType?.toScopedAst(scope);
     FunctionBody methodBody = _returnExpression?.toFunctionBody();
     if (static) {
       methodAst.modifierKeyword = _static;
@@ -123,12 +129,15 @@ class MethodBuilder implements CodeBuilder<Declaration> {
     }
     if (_parameters.isNotEmpty) {
       methodAst.parameters.parameters
-          .addAll(_parameters.map/*<FormalParameter>*/((p) => p.toAst()));
+          .addAll(_parameters.map/*<FormalParameter>*/((p) => p.toScopedAst(scope)));
     }
     methodAst.body = methodBody;
     return methodAst;
   }
 
+  @override
+  Declaration toScopedAst(Scope scope) => toFunctionAst(scope: scope);
+
   @override
   String toString() => 'MethodBuilder ${toAst().toSource()}';
 
@@ -156,7 +165,7 @@ class MethodBuilder implements CodeBuilder<Declaration> {
           _blockBody(),
         ),
       );
-
+  // TODO: implement requiredImports
   static MethodDeclaration _emptyMethod() => new MethodDeclaration(
         null,
         null,