add support for evaluating private identifiers and inlining the result into the bootstrap

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b9baa6b..0abd507 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.6.0+2
+
+* Private identifiers will now be evaluated and inlined into the bootstrap file
+by the transformer, [29](https://github.com/dart-lang/initialize/issues/29).
+
 ## 0.6.0+1
 
 * Fix for `LibraryIdentifier` paths when initializer starts from inline scripts

diff --git a/lib/build/initializer_plugin.dart b/lib/build/initializer_plugin.dart
index 466065f..8822dc4 100644
--- a/lib/build/initializer_plugin.dart
+++ b/lib/build/initializer_plugin.dart

@@ -229,24 +229,27 @@
       buffer.write('}');
     } else if (expression is Identifier) {
       var element = expression.bestElement;
-      if (element == null || !element.isPublic) {
-        logger.error('Private constants are not supported in intializer '
-            'constructors, found $element.');
-      }
-      libraryPrefixes.putIfAbsent(
+      if (element == null) {
+        logger.error('Unable to get `bestElement` for expression: $expression');
+      } else if (!element.isPublic) {
+        // Inline the evaluated value of private identifiers.
+        buffer.write(_evaluateExpression(expression, pluginData));
+      } else {
+        libraryPrefixes.putIfAbsent(
           element.library, () => 'i${libraryPrefixes.length}');
 
-      buffer.write('${libraryPrefixes[element.library]}.');
-      if (element is ClassElement) {
-        buffer.write(element.name);
-      } else if (element is PropertyAccessorElement) {
-        var variable = element.variable;
-        if (variable is FieldElement) {
-          buffer.write('${variable.enclosingElement.name}.');
+        buffer.write('${libraryPrefixes[element.library]}.');
+        if (element is ClassElement) {
+          buffer.write(element.name);
+        } else if (element is PropertyAccessorElement) {
+          var variable = element.variable;
+          if (variable is FieldElement) {
+            buffer.write('${variable.enclosingElement.name}.');
+          }
+          buffer.write('${variable.name}');
+        } else {
+          logger.error('Unsupported argument to initializer constructor.');
         }
-        buffer.write('${variable.name}');
-      } else {
-        logger.error('Unsupported argument to initializer constructor.');
       }
     } else if (expression is PropertyAccess) {
       buffer.write(buildExpression(expression.target, pluginData));
@@ -256,26 +259,32 @@
           'Instance creation expressions are not supported (yet). Instead, '
           'please assign it to a const variable and use that instead.');
     } else {
-      // Try to evaluate the constant and use that.
-      var result = pluginData.resolver.evaluateConstant(
-          pluginData.initializer.targetElement.library, expression);
-      if (!result.isValid) {
-        logger.error('Invalid expression in initializer, found $expression. '
-            'And got the following errors: ${result.errors}.');
-      }
-      var value = result.value.value;
-      if (value == null) {
-        logger.error('Unsupported expression in initializer, found '
-            '$expression. Please file a bug at '
-            'https://github.com/dart-lang/initialize/issues');
-      }
-
-      if (value is String) value = _stringValue(value);
-      buffer.write(value);
+      buffer.write(_evaluateExpression(expression, pluginData));
     }
     return buffer.toString();
   }
 
+  _evaluateExpression(Expression expression, InitializerPluginData pluginData) {
+    var logger = pluginData.logger;
+    var result = pluginData.resolver.evaluateConstant(
+        pluginData.initializer.targetElement.library, expression);
+    if (!result.isValid) {
+      logger.error('Invalid expression in initializer, found $expression. '
+          'And got the following errors: ${result.errors}.');
+      return null;
+    }
+    var value = result.value.value;
+    if (value == null) {
+      logger.error('Unsupported expression in initializer, found '
+          '$expression. Please file a bug at '
+          'https://github.com/dart-lang/initialize/issues');
+      return null;
+    }
+
+    if (value is String) value = _stringValue(value);
+    return value;
+  }
+
   // Returns an expression for a string value. Wraps it in single quotes and
   // escapes existing single quotes and escapes.
   _stringValue(String value) {

diff --git a/pubspec.yaml b/pubspec.yaml
index 21298d9..2d0b048 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml

@@ -1,5 +1,5 @@
 name: initialize
-version: 0.6.0+1
+version: 0.6.0+2
 author: Polymer.dart Authors <web@dartlang.org>
 description: Generic building blocks for doing static initialization.
 homepage: https://github.com/dart-lang/initialize

diff --git a/test/transformer_test.dart b/test/transformer_test.dart
index 8b43d45..d9c6130 100644
--- a/test/transformer_test.dart
+++ b/test/transformer_test.dart

@@ -116,6 +116,7 @@
   testPhases('constructor arguments', phases, {
     'a|web/index.dart': '''
         @DynamicInit(foo)
+        @DynamicInit(_foo)
         @DynamicInit(Foo.foo)
         @DynamicInit(bar.Foo.bar)
         @DynamicInit(bar.Foo.foo)
@@ -139,6 +140,7 @@
 
         const x = 'x';
         const y = 'y';
+        const _foo = '_foo';
 
         class MyConst {
           const MyConst;
@@ -172,6 +174,7 @@
         main() {
           initializers.addAll([
             new InitEntry(const i1.DynamicInit(i2.foo), const LibraryIdentifier(#web_foo, null, 'index.dart')),
+            new InitEntry(const i1.DynamicInit('_foo'), const LibraryIdentifier(#web_foo, null, 'index.dart')),
             new InitEntry(const i1.DynamicInit(i2.Foo.foo), const LibraryIdentifier(#web_foo, null, 'index.dart')),
             new InitEntry(const i1.DynamicInit(i2.Foo.bar), const LibraryIdentifier(#web_foo, null, 'index.dart')),
             new InitEntry(const i1.DynamicInit(i2.Foo.foo), const LibraryIdentifier(#web_foo, null, 'index.dart')),