Fixes handling of double mustache in UiBinder.

In UiBinder, when an attiribute is set to an expression with double mustache
the first curly bracket disappears.
 e.g. {{p in posts}} becomes {p in posts}}
This is related to some undocumented behavior to disable field reference
resoulution but it is pretty bad and  makes it diffucult to integrate UiBinder
with runtime templating systems like Polymer.

This patch introduces a  new escaping option: \{ABC} becomes {ABC} and not
treated as a field reference. In addition, double mustache is also not treated
as field reference nor replaced due escaping so that it will be correctly
preserved in the final output.

Change-Id: I24a202f3165a8ecdca8fb419e9c3197818df87b5

user/src/com/google/gwt/uibinder/attributeparsers/FieldReferenceConverter.java

@@ -42,8 +42,11 @@
  * dashes are converted to camel case. That is, {able.baker-charlie} is the same
  * as {able.bakerCharlie}
  * <p>
- * Opening braces may be escape by doubling them. That is, "{{foo}" will
- * converted to "{foo}", with no field reference detected.
+ * Double mustaches (i.e. "{{..}}") are not matched as references to play well
+ * with modern templating systems.
+ * <p>
+ * Opening braces may be escape by slash. That is, "\{foo}" will converted to
+ * "{foo}", with no field reference detected.
  */
 public class FieldReferenceConverter {
   /**
@@ -176,12 +179,17 @@ public String convert(XMLElement source, String in, Delegate delegate) {
     Matcher m = BRACES.matcher(in);
     while (m.find(nextFindStart)) {
       String fieldReference = m.group(1);
-      if (!legalFirstCharacter(fieldReference)) {
-        nextFindStart = m.start() + 2;
+      int start = m.start();
+      if (!isLegalPreviousCharacter(in, start)) {
+        nextFindStart = start + 1;
+        continue;
+      }
+      if (!isLegalFirstCharacter(fieldReference)) {
+        nextFindStart = start + 2;
         continue;
       }
 
-      String precedingFragment = in.substring(lastMatchEnd, m.start());
+      String precedingFragment = in.substring(lastMatchEnd, start);
       precedingFragment = handleFragment(precedingFragment, delegate);
       b.append(precedingFragment);
 
@@ -220,11 +228,19 @@ private String expandDots(String value) {
   }
 
   private String handleFragment(String fragment, Delegate delegate) {
-    fragment = fragment.replace("{{", "{");
+    fragment = fragment.replace("\\{", "{");
     return delegate.handleFragment(fragment);
   }
 
-  private boolean legalFirstCharacter(String fieldReference) {
+  private boolean isLegalFirstCharacter(String fieldReference) {
     return LEGAL_FIRST_CHAR.matcher(fieldReference).matches();
   }
+
+  private boolean isLegalPreviousCharacter(String in, int start) {
+    if (start < 1) {
+      return true;
+    }
+    char previousChar = in.charAt(start - 1);
+    return previousChar != '{' && previousChar != '\\';
+  }
 }

user/src/com/google/gwt/uibinder/elementparsers/ComputedAttributeInterpreter.java

@@ -71,7 +71,7 @@ public String interpretElement(XMLElement elem)
          * TODO(rjrjr) Move this to XMLElement RSN
          */
         String n = att.getName();
-        String v = att.consumeRawValue().replace("{{", "{");
+        String v = att.consumeRawValue().replace("\\{", "{");
         elem.setAttribute(n, v);
       }
     }

user/test/com/google/gwt/uibinder/attributeparsers/FieldReferenceConverterTest.java

@@ -60,7 +60,7 @@ public void testOne() {
 
     assertEquals(expected, converter.convert(before, frDelegate));
   }
-  
+
   public void testReplaceSimple() {
     String before = "able {baker} charlie";
     String expected = "*able * & baker & * charlie*";
@@ -83,7 +83,7 @@ public void testReplaceSeveral() {
   }
 
   public void testEscaping() {
-    String before = "Well {{Hi mom}!";
+    String before = "Well \\{Hi mom}!";
     String expected = "*Well {Hi mom}!*";
 
     assertEquals(expected, converter.convert(before, frDelegate));
@@ -96,6 +96,13 @@ public void testIgnoreEmpty() {
     assertEquals(expected, converter.convert(before, frDelegate));
   }
 
+  public void testIgnoreMustache() {
+    String before = "{{abc.dfc in klm}}";
+    String expected = "*{{abc.dfc in klm}}*";
+
+    assertEquals(expected, converter.convert(before, frDelegate));
+  }
+
   public void testIgnoreNonIdentifierFirstChar() {
     String before = "Hi { } mom, how { are } {1you}?";
     String expected = "*Hi { } mom, how { are } {1you}?*";
@@ -105,6 +112,8 @@ public void testIgnoreNonIdentifierFirstChar() {
 
   public void testHasFieldReferences() {
     assertTrue(FieldReferenceConverter.hasFieldReferences("{able} {baker}"));
+    assertFalse(FieldReferenceConverter.hasFieldReferences("{{able}}"));
     assertFalse(FieldReferenceConverter.hasFieldReferences("{{able} baker { Charlie }"));
+    assertFalse(FieldReferenceConverter.hasFieldReferences("\\{able} baker { Charlie }"));
   }
 }

user/test/com/google/gwt/uibinder/test/client/UiBinderTest.java

@@ -165,6 +165,7 @@ public void testAllowIdOnDomElements() {
   public void testBraceEscaping() {
     assertEquals("blah di blah {foo: \"bar\"} di blah",
         widgetUi.bracedParagraph.getAttribute("fnord"));
+    assertEquals("{{blah in blah}}", widgetUi.bracedParagraph.getAttribute("doubleMustache"));
   }
 
   public void testBundle() {

user/test/com/google/gwt/uibinder/test/client/WidgetBasedUi.ui.xml

@@ -201,9 +201,9 @@
   </gwt:Dock>
   <gwt:Dock direction='CENTER'>
     <gwt:HTMLPanel>
-      <p ui:field='bracedParagraph' fnord='blah di blah {{foo: "bar"} di blah'
-        foo='{CONST_FOO}' bar='{CONST_BAR} {CONST_BAZ}'
-        enum='{ENUM_1.name} {ENUM_2.name}' ><ui:msg>This is a
+      <p ui:field='bracedParagraph' fnord='blah di blah \{foo: "bar"} di blah'
+        foo='{CONST_FOO}' bar='{CONST_BAR} {CONST_BAZ}' enum='{ENUM_1.name} {ENUM_2.name}'
+        doubleMustache="{{blah in blah}}" > <ui:msg>This is a
       demonstration and test bed of GWT's shiny UiBinder
       package. At the moment it works mainly as described in
       <a href="http://code.google.com/p/google-web-toolkit-incubator/wiki/DeclarativeUi"