Type annotations instead of closure comments.

lib/src/js/printer.dart

Index: lib/src/js/printer.dart
diff --git a/lib/src/js/printer.dart b/lib/src/js/printer.dart
index 02bf379a74871a8b82bd27ef89827c59c42b1c54..cc347255cb69d824453503dc5aeac5ba30f5cda4 100644
--- a/lib/src/js/printer.dart
+++ b/lib/src/js/printer.dart
@@ -9,6 +9,7 @@ class JavaScriptPrintingOptions {
   final bool shouldCompressOutput;
   final bool minifyLocalVariables;
   final bool preferSemicolonToNewlineInMinifiedOutput;
+  final bool shouldEmitTypes;
   final bool allowSingleLineIfStatements;
 
   /// True to allow keywords in properties, such as `obj.var` or `obj.function`
@@ -19,6 +20,7 @@ class JavaScriptPrintingOptions {
       {this.shouldCompressOutput: false,
        this.minifyLocalVariables: false,
        this.preferSemicolonToNewlineInMinifiedOutput: false,
+       this.shouldEmitTypes: false,
        this.allowKeywordsInProperties: false,
        this.allowSingleLineIfStatements: false});
 }
@@ -51,8 +53,9 @@ class SimpleJavaScriptPrintingContext extends JavaScriptPrintingContext {
   String getText() => buffer.toString();
 }
 
-
-class Printer implements NodeVisitor {
+// TODO(ochafik): Inline the body of [TypeScriptTypePrinter] here if/when it no
+// longer needs to share utils with [ClosureTypePrinter].
+class Printer extends TypeScriptTypePrinter implements NodeVisitor {
   final JavaScriptPrintingOptions options;
   final JavaScriptPrintingContext context;
   final bool shouldCompressOutput;
@@ -541,12 +544,14 @@ class Printer implements NodeVisitor {
                             newInForInit: false, newAtStatementBegin: false);
     }
     localNamer.enterScope(fun);
+    outTypeParams(fun.typeParams);
     out("(");
     if (fun.params != null) {
       visitCommaSeparated(fun.params, PRIMARY,
                           newInForInit: false, newAtStatementBegin: false);
     }
     out(")");
+    outTypeAnnotation(fun.returnType);
     switch (fun.asyncModifier) {
       case const AsyncModifier.sync():
         break;
@@ -601,8 +606,11 @@ class Printer implements NodeVisitor {
 
   visitVariableDeclarationList(VariableDeclarationList list) {
     outClosureAnnotation(list);
-    out(list.keyword);
-    out(" ");
+    // Note: keyword can be null for non-static field declarations.
+    if (list.keyword != null) {
+      out(list.keyword);
+      out(" ");
+    }
     visitCommaSeparated(list.declarations, ASSIGNMENT,
                         newInForInit: inForInit, newAtStatementBegin: false);
   }
@@ -639,6 +647,7 @@ class Printer implements NodeVisitor {
       }
       visit(node.structure);
     }
+    outTypeAnnotation(node.type);
     if (node.defaultValue != null) {
       spaceOut();
       out("=");
@@ -869,6 +878,7 @@ class Printer implements NodeVisitor {
 
   visitIdentifier(Identifier node) {
     out(localNamer.getName(node));
+    outTypeAnnotation(node.type);
   }
 
   visitRestParameter(RestParameter node) {
@@ -934,7 +944,8 @@ class Printer implements NodeVisitor {
 
   visitArrowFun(ArrowFun fun) {
     localNamer.enterScope(fun);
-    if (fun.params.length == 1) {
+    if (fun.params.length == 1 &&
+        (fun.params.single.type == null || !options.shouldEmitTypes)) {
       visitNestedExpression(fun.params.single, SPREAD,
           newInForInit: false, newAtStatementBegin: false);
     } else {
@@ -943,6 +954,7 @@ class Printer implements NodeVisitor {
           newInForInit: false, newAtStatementBegin: false);
       out(")");
     }
+    outTypeAnnotation(fun.returnType);
     spaceOut();
     out("=>");
     if (fun.body is Expression) {
@@ -1081,9 +1093,23 @@ class Printer implements NodeVisitor {
     lineOut();
   }
 
+  void outTypeParams(Iterable<Identifier> typeParams) {
+    if (typeParams != null && options.shouldEmitTypes && typeParams.isNotEmpty) {
+      out("<");
+      var first = true;
+      for (var typeParam in typeParams) {
+        if (!first) out(", ");
+        first = false;
+        visit(typeParam);
+      }
+      out(">");
+    }
+  }
+
   visitClassExpression(ClassExpression node) {
     out('class ');
     visit(node.name);
+    outTypeParams(node.typeParams);
     if (node.heritage != null) {
       out(' extends ');
       visit(node.heritage);
@@ -1093,6 +1119,14 @@ class Printer implements NodeVisitor {
       out('{');
       lineOut();
       indentMore();
+      if (options.shouldEmitTypes && node.fields != null) {
+        for (var field in node.fields) {
+          indent();
+          visit(field);
+          out(";");
+          lineOut();
+        }
+      }
       for (var method in node.methods) {
         indent();
         visit(method);
@@ -1324,6 +1358,18 @@ class Printer implements NodeVisitor {
     out("await ");
     visit(node.expression);
   }
+
+  void outTypeAnnotation(TypeRef node) {
+    if (node == null || !options.shouldEmitTypes || node.isUnknown) return;
+
+    if (node is OptionalTypeRef) {
+      out("?: ");
+      visit(node.type);
+    } else {
+      out(": ");
+      visit(node);
+    }
+  }
 }
 
 // Collects all the var declarations in the function.  We need to do this in a