Reapply "Fix issues with field names by ensuring that fields have exactly one name regardless of ho…

sdk/lib/_internal/compiler/implementation/js_backend/namer.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
index e22454b9d7c423ac28d4d59d52eb8d5cb9bf1733..40209b2a5a7f18aef579d46ba40e63c194ed3fc5 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
@@ -226,6 +226,9 @@ class Namer implements ClosureNamer {
   // Name of property in a class description for the native dispatch metadata.
   final String nativeSpecProperty = '%';
 
+  static final RegExp IDENTIFIER = new RegExp(r'^[A-Za-z_$][A-Za-z0-9_$]*$');
+  static final RegExp NON_IDENTIFIER_CHAR = new RegExp(r'[^A-Za-z_0-9$]');
+
   /**
    * Map from top-level or static elements to their unique identifiers provided
    * by [getName].
@@ -440,29 +443,64 @@ class Namer implements ClosureNamer {
   String invocationMirrorInternalName(Selector selector)
       => invocationName(selector);
 
-  String instanceFieldName(Element element) {
+  /**
+   * Returns name of accessor (root to getter and setter) for a static or
+   * instance field.
+   */
+  String fieldAccessorName(Element element) {
+    return element.isInstanceMember()
+        ? instanceFieldAccessorName(element)
+        : getNameOfField(element);
+  }
+
+  /**
+   * Returns name of the JavaScript property used to store a static or instance
+   * field.
+   */
+  String fieldPropertyName(Element element) {
+    return element.isInstanceMember()
+        ? instanceFieldPropertyName(element)
+        : getNameOfField(element);
+  }
+
+  /**
+   * Returns name of accessor (root to getter and setter) for an instance field.
+   */
+  String instanceFieldAccessorName(Element element) {
     String proposedName = privateName(element.getLibrary(), element.name);
     return getMappedInstanceName(proposedName);
   }
 
-  // Construct a new name for the element based on the library and class it is
-  // in.  The name here is not important, we just need to make sure it is
-  // unique.  If we are minifying, we actually construct the name from the
-  // minified versions of the class and instance names, but the result is
-  // minified once again, so that is not visible in the end result.
-  String shadowedFieldName(Element fieldElement) {
-    // Check for following situation: Native field ${fieldElement.name} has
-    // fixed JSName ${fieldElement.nativeName()}, but a subclass shadows this
-    // name.  We normally handle that by renaming the superclass field, but we
-    // can't do that because native fields have fixed JavaScript names.
-    // In practice this can't happen because we can't inherit from native
-    // classes.
-    assert (!fieldElement.hasFixedBackendName());
+  /**
+   * Returns name of the JavaScript property used to store an instance field.
+   */
+  String instanceFieldPropertyName(Element element) {
+    if (element.hasFixedBackendName()) {
+      return element.fixedBackendName();
+    }
+    // If a class is used anywhere as a mixin, we must make the name unique so
+    // that it does not accidentally shadow.  Also, the mixin name must be
+    // constant over all mixins.
+    if (compiler.world.isUsedAsMixin(element.getEnclosingClass()) ||
+        shadowingAnotherField(element)) {
+      // Construct a new name for the element based on the library and class it
+      // is in.  The name here is not important, we just need to make sure it is
+      // unique.  If we are minifying, we actually construct the name from the
+      // minified version of the class name, but the result is minified once
+      // again, so that is not visible in the end result.
+      String libraryName = getNameOfLibrary(element.getLibrary());
+      String className = getNameOfClass(element.getEnclosingClass());
+      String instanceName = privateName(element.getLibrary(), element.name);
+      return getMappedInstanceName('$libraryName\$$className\$$instanceName');
+    }
 
-    String libraryName = getNameOfLibrary(fieldElement.getLibrary());
-    String className = getNameOfClass(fieldElement.getEnclosingClass());
-    String instanceName = instanceFieldName(fieldElement);
-    return getMappedInstanceName('$libraryName\$$className\$$instanceName');
+    String proposedName = privateName(element.getLibrary(), element.name);
+    return getMappedInstanceName(proposedName);
+  }
+
+
+  bool shadowingAnotherField(Element element) {
+    return element.getEnclosingClass().hasFieldShadowedBy(element);
   }
 
   String setterName(Element element) {
@@ -592,6 +630,15 @@ class Namer implements ClosureNamer {
             ? name.substring(name.lastIndexOf('.') + 1)
             : name.substring(0, name.indexOf('.'));
       }
+      // The filename based name can contain all kinds of nasty characters. Make
+      // sure it is an identifier.
+      if (!IDENTIFIER.hasMatch(name)) {
+        name = name.replaceAllMapped(NON_IDENTIFIER_CHAR,
+            (match) => match[0].codeUnitAt(0).toRadixString(16));
+        if (!IDENTIFIER.hasMatch(name)) {  // e.g. starts with digit.
+          name = 'lib_$name';
+        }
+      }
     } else {
       name = element.name;
     }
@@ -718,7 +765,9 @@ class Namer implements ClosureNamer {
       } else if (element.kind == ElementKind.SETTER) {
         return setterName(element);
       } else if (element.kind == ElementKind.FIELD) {
-        return instanceFieldName(element);
+        compiler.internalError(
+            'use instanceFieldPropertyName or instanceFieldAccessorName',
+            node: element.parseNode(compiler));
       } else {
         compiler.internalError('getName for bad kind: ${element.kind}',
                                node: element.parseNode(compiler));