Rendering nice unicode arrow for function types in UI.

compiler/frontend/src/org/jetbrains/jet/renderer/DescriptorRendererImpl.java

@@ -116,6 +116,17 @@ public class DescriptorRendererImpl implements DescriptorRenderer {
         return escape("<");
     }
 
+    @NotNull
+    private String arrow() {
+        switch (textFormat) {
+            case PLAIN:
+                return escape("->");
+            case HTML:
+                return "&rarr;";
+        }
+        throw new IllegalStateException("Unexpected textFormat: " + textFormat);
+    }
+
     @NotNull
     private String renderMessage(@NotNull String message) {
         switch (textFormat) {
@@ -188,7 +199,7 @@ public class DescriptorRendererImpl implements DescriptorRenderer {
             return "???";
         }
         else if (type == CallResolverUtil.PLACEHOLDER_FUNCTION_TYPE) {
-            return "??? -> ???";
+            return "??? " + arrow() + " ???";
         }
         else if (ErrorUtils.isErrorType(type)) {
             return type.toString();
@@ -258,7 +269,7 @@ public class DescriptorRendererImpl implements DescriptorRenderer {
 
         sb.append("(");
         appendTypeProjections(KotlinBuiltIns.getInstance().getParameterTypeProjectionsFromFunctionType(type), sb);
-        sb.append(") -> ");
+        sb.append(") " + arrow() + " ");
         sb.append(renderType(KotlinBuiltIns.getInstance().getReturnTypeFromFunctionType(type)));
 
         if (type.isNullable()) {

idea/testData/diagnosticMessage/functionPlaceholder1.html

@@ -36,7 +36,7 @@ cannot be applied to</td>
 <td align="right" style="white-space:nowrap;">
 <font color=red>
 <b>
-??? -&gt; ???</b>
+??? &rarr; ???</b>
 </font>
 </td>
 <td style="white-space:nowrap;">

idea/testData/diagnosticMessage/functionPlaceholder2.html

@@ -36,7 +36,7 @@ cannot be applied to</td>
 <td align="right" style="white-space:nowrap;">
 <font color=red>
 <b>
-(???) -&gt; ???</b>
+(???) &rarr; ???</b>
 </font>
 </td>
 <td style="white-space:nowrap;">

idea/testData/diagnosticMessage/functionPlaceholder3.html

@@ -36,7 +36,7 @@ cannot be applied to</td>
 <td align="right" style="white-space:nowrap;">
 <font color=red>
 <b>
-(jet.Int) -&gt; ???</b>
+(jet.Int) &rarr; ???</b>
 </font>
 </td>
 <td style="white-space:nowrap;">