support more types of expressions

lib/build/initializer_plugin.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 library initialize.build.initializer_plugin;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:barback/barback.dart';
 import 'package:code_transformers/resolver.dart';
 import 'package:initialize/transformer.dart';
@@ skipping 184 matching lines @@
     return buffer.toString();
   }
 
   /// Builds a [String] representing [expression] taking into account the
   /// [libraryPrefixes] from [pluginData].
   String buildExpression(
       Expression expression, InitializerPluginData pluginData) {
     var logger = pluginData.logger;
     var libraryPrefixes = pluginData.libraryPrefixes;
     var buffer = new StringBuffer();
-    if (expression is StringLiteral) {
-      var value = expression.stringValue;
-      if (value == null) {
-        logger.error('Only const strings are allowed in initializer '
-            'expressions, found $expression');
-      }
-      value = value.replaceAll(r'\', r'\\').replaceAll(r"'", r"\'");
-      buffer.write("'$value'");
+    if (expression is StringLiteral && expression.stringValue != null) {
+      buffer.write(_stringValue(expression.stringValue));
     } else if (expression is BooleanLiteral ||
         expression is DoubleLiteral ||
         expression is IntegerLiteral ||
         expression is NullLiteral) {
       buffer.write('${expression}');
     } else if (expression is ListLiteral) {
       buffer.write('const [');
       var first = true;
       for (Expression listExpression in expression.elements) {
         if (!first) buffer.write(', ');
         first = false;
         buffer.write(buildExpression(listExpression, pluginData));
       }
       buffer.write(']');
     } else if (expression is MapLiteral) {
       buffer.write('const {');
       var first = true;
       for (MapLiteralEntry entry in expression.entries) {
         if (!first) buffer.write(', ');
         first = false;
         buffer.write(buildExpression(entry.key, pluginData));
         buffer.write(': ');
         buffer.write(buildExpression(entry.value, pluginData));
       }
       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.');
+        'constructors, found $element.');
       }
       libraryPrefixes.putIfAbsent(
           element.library, () => 'i${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('${variable.name}');
       } else {
         logger.error('Unsupported argument to initializer constructor.');
       }
+    } else if (expression is InstanceCreationExpression) {
+      logger.error('Unsupported expression in initializer, found $expression. '
+          'Instance creation expressions are not supported (yet). Instead, '
+          'please assign it to a const variable and use that instead.');
     } else {
-      logger.error('Only literals and identifiers are allowed for initializer '
-          'expressions, found $expression.');
+      // 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);

[Siggi Cherem (dart-lang), 2015/02/25 19:32:08]

we might need to check for instance creations here as well. 

For example, I'm not sure if we handle this correctly:

a.dart:
  @HtmlImport(b.foo);
  library a;

  import 'b.dart' as b;

b.dart:
  const foo = const Foo()
  

This will get normalized to the value `const Foo()` here, I believe

[jakemac, 2015/02/25 20:23:05]

Above this there is a special case for Identifiers, they aren't evaluated but
just left alone (and prefixed). The `constructor arguments` test has an example
of this.

This code path is just for expressions that aren't simple literals, identifiers,
or constructors.

[Siggi Cherem (dart-lang), 2015/02/25 21:06:33]

but is there any case where those could evaluate to a constructor as a result?

[jakemac, 2015/02/25 22:06:08]

Done.

+      buffer.write(value);
     }
     return buffer.toString();
   }
+
+  // Returns an expression for a string value. Wraps it in single quotes and
+  // escapes existing single quotes and escapes.
+  _stringValue(String value) {
+    value = value.replaceAll(r'\', r'\\').replaceAll(r"'", r"\'");
+    return "'$value'";
+  }
 }