fix #30094, assert should work with a function

pkg/dev_compiler/lib/src/compiler/code_generator.dart

Index: pkg/dev_compiler/lib/src/compiler/code_generator.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/code_generator.dart b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
index 0151900afd6df6da23c1411172288eb7f688fbbf..75535faa7df093f1237ef6cac8eba245a83acf35 100644
--- a/pkg/dev_compiler/lib/src/compiler/code_generator.dart
+++ b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
@@ -3953,19 +3953,30 @@ class CodeGenerator extends Object
   @override
   JS.Statement visitAssertStatement(AssertStatement node) {
     // TODO(jmesserly): only emit in checked mode.
+    var condition = node.condition;
+    var conditionType = condition.staticType;
+    JS.Expression jsCondition = _visit(condition);
+
+    var assertHelper = 'assert';
+    if (conditionType is FunctionType &&
+        conditionType.parameters.isEmpty &&
+        conditionType.returnType == types.boolType) {
+      jsCondition = new JS.Call(jsCondition, []);
+    } else if (conditionType != types.boolType) {
+      assertHelper = 'dassert';
+    }
+    var args = [jsCondition];
     if (node.message != null) {
-      return _callHelperStatement('assert(#, () => #);',
-          [_visit(node.condition), _visit(node.message)]);
+      args.add(js.call('() => #', [_visit(node.message)]));
     }
-
-    return _callHelperStatement('assert(#);', _visit(node.condition));
+    return _callHelperStatement('$assertHelper(#);', [args]);
   }
 
   @override
   JS.Statement visitReturnStatement(ReturnStatement node) {
     var e = node.expression;
     if (e == null) return new JS.Return();
-    return (_visit(e) as JS.Expression).toReturn();
+    return _visit<JS.Expression>(e).toReturn();
   }
 
   @override
@@ -4977,8 +4988,8 @@ class CodeGenerator extends Object
       // dynamic dispatch
       var dynamicHelper = const {'[]': 'dindex', '[]=': 'dsetindex'}[name];
       if (dynamicHelper != null) {
-        return _callHelper('$dynamicHelper(#, #)',
-            [_visit(target) as JS.Expression, _visitList(args)]);
+        return _callHelper(
+            '$dynamicHelper(#, #)', [_visit(target), _visitList(args)]);
       } else {
         return _callHelper(
             'dsend(#, #, #)', [_visit(target), memberName, _visitList(args)]);