Add some support for the code-point code-unit distinction.

sdk/lib/_internal/compiler/implementation/lib/js_helper.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
index 5b4f36a612dd73f37a56a7c035d18e5b31ec40dd..6d05190f6c909fd747a384fae44bda4c5b69dea4 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
@@ -534,11 +534,45 @@ class Primitives {
 
   static num dateNow() => JS('num', r'Date.now()');
 
+  static const MAX_CODE_UNIT = 0xffff;
+  static const MAX_CODE_POINT = 0x10ffff;
+  static const SURROGATE_BASE = 0xd800;
+  static const SURROGATE_END = 0xdfff;
+  static const LEAD_BASE = 0xd800;
+  static const TRAIL_BASE = 0xdc00;
+  static const SURROGATE_MASK = 0x3ff;
+  static const SURROGATE_ENCODING_BASE = 0x10000;
+
   static String stringFromCharCodes(charCodes) {

[floitsch, 2012/11/08 15:28:21]

I would move this code to the patch-class and redirect to fromCodeUnits there.
Maybe ask the others first what they think.

[ngeoffray, 2012/11/15 13:24:20]

I don't think the patch classes have access to 'JS', so I would keep the method
where it is. The less libraries that touch JS, the better.

+    bool surrogatePairs = false;
+    for (var i in charCodes) {
+      if (i is !int) throw new ArgumentError(i);
+      if (i > MAX_CODE_POINT) throw new ArgumentError(i);
+      if (i > MAX_CODE_UNIT) surrogatePairs = true;
+      if (i >= SURROGATE_BASE && i <= SURROGATE_END) throw new ArgumentError(i);
+    }
+    if (!surrogatePairs) {
+      return JS('String', r'String.fromCharCode.apply(#, #)', null, charCodes);
+    }
+    var expanded = [];
     for (var i in charCodes) {
+      if (i <= MAX_CODE_UNIT) {
+        expanded.add(i);
+      } else {
+        expanded.add(LEAD_BASE +
+                     (((i - SURROGATE_ENCODING_BASE) >> 10) & SURROGATE_MASK));
+        expanded.add(TRAIL_BASE + (i & SURROGATE_MASK));
+      }
+    }
+    return JS('String', r'String.fromCharCode.apply(#, #)', null, expanded);
+  }
+
+  static String stringFromCodeUnits(codeUnits) {
+    for (var i in codeUnits) {
       if (i is !int) throw new ArgumentError(i);
+      if (i > MAX_CODE_UNIT) throw new ArgumentError(i);
     }
-    return JS('String', r'String.fromCharCode.apply(#, #)', null, charCodes);
+    return JS('String', r'String.fromCharCode.apply(#, #)', null, codeUnits);
   }
 
   static String getTimeZoneName(receiver) {