Parse optional and named parameters.

pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart

Index: pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
index a63af7f9ac69314a36f08e0b54e96eb0793914d4..2cc7c099aadd40636a0a3fd8b9e94d43e27957bb 100644
--- a/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
+++ b/pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart
@@ -9,6 +9,8 @@ import 'package:analyzer/dart/ast/ast_factory.dart' show AstFactory;
 import 'package:analyzer/dart/ast/standard_ast_factory.dart' as standard;
 import 'package:analyzer/dart/ast/token.dart' as analyzer show Token;
 import 'package:analyzer/dart/element/element.dart' show Element;
+import 'package:front_end/src/fasta/parser/parser.dart'
+    show FormalParameterType;
 import 'package:front_end/src/fasta/scanner/token.dart'
     show BeginGroupToken, Token;
 import 'package:kernel/ast.dart' show AsyncMarker;
@@ -491,17 +493,44 @@ class AstBuilder extends ScopeListener {
     push(ast.throwExpression(toAnalyzerToken(throwToken), pop()));
   }
 
-  void endFormalParameter(Token thisKeyword) {
+  @override
+  void endOptionalFormalParameters(
+      int count, Token beginToken, Token endToken) {
+    debugEvent("OptionalFormalParameters");
+  }
+
+  void handleValuedFormalParameter(Token equals, Token token) {
+    debugEvent("ValuedFormalParameter");
+    Expression value = pop();
+    push(new _ParameterDefaultValue(equals, value));
+  }
+
+  void handleFormalParameterWithoutValue(Token token) {
+    debugEvent("FormalParameterWithoutValue");
+    push(_ParameterDefaultValue.nullValue);

[Paul Berry, 2017/02/22 20:50:04]

Personally I would prefer to use the enum NullValue for this (see
pkg/front_end/lib/src/fasta/source/stack_listener.dart).  You'll have to add a
new value to the enum (e.g. NullValue.parameterDefault).

The pop() method automatically converts NullValue enums to `null`, so if you do
this, then line 526 changes to simply "if (defaultValue != null)"

[ahe, 2017/02/23 14:54:49]

I agree. Don't hesitate to add values to that enum as you need them, its only
there to help us debug listeners.

[scheglov, 2017/02/23 17:55:10]

Done.

+  }
+
+  void endFormalParameter(Token thisKeyword, FormalParameterType kind) {
     debugEvent("FormalParameter");
     if (thisKeyword != null) {
       internalError("'this' can't be used here.");
     }
+    _ParameterDefaultValue defaultValue = pop();
     SimpleIdentifier name = pop();
     TypeName type = pop();
     Token keyword = _popOptionalSingleModifier();
     pop(); // Metadata.
-    SimpleFormalParameter node = ast.simpleFormalParameter(
+    FormalParameter node = ast.simpleFormalParameter(
         null, null, toAnalyzerToken(keyword), type, name);
+
+    if (defaultValue.separator != null) {
+      node = ast.defaultFormalParameter(
+          node,
+          _toAnalyzerParameterKind(kind),
+          toAnalyzerToken(defaultValue.separator),
+          defaultValue.value);
+    }
+
     scope[name.name] = name.staticElement = new AnalyzerParameterElement(node);
     push(node);
   }
@@ -1138,6 +1167,17 @@ class AstBuilder extends ScopeListener {
       return null;
     }
   }
+
+  ParameterKind _toAnalyzerParameterKind(FormalParameterType type) {
+    if (type == FormalParameterType.POSITIONAL) {
+      return ParameterKind.POSITIONAL;
+    } else

[Paul Berry, 2017/02/22 20:50:05]

Nit: run dartfmt

+    if (type == FormalParameterType.NAMED) {
+      return ParameterKind.NAMED;
+    } else {
+      return ParameterKind.REQUIRED;
+    }
+  }
 }
 
 /// Data structure placed on the stack to represent a class body.
@@ -1170,3 +1210,14 @@ class _MixinApplication {
 
   _MixinApplication(this.supertype, this.withKeyword, this.mixinTypes);
 }
+
+/// Data structure placed on the stack to represent the default parameter
+/// value with the separator token.
+class _ParameterDefaultValue {
+  static final nullValue = new _ParameterDefaultValue(null, null);

[Paul Berry, 2017/02/22 20:50:05]

Nit: make this const.

(Or delete it if you take my advice above about using NullValue).

+
+  final Token separator;
+  final Expression value;
+
+  _ParameterDefaultValue(this.separator, this.value);
+}