Hot fix for missing ko.unwrap in Linq Last,First,ElementA translations

This is a lighterweight alternative to #1870,
which we might not want to merge to 4.3.
This PR does only fixes the 4.3 regression,
the problem with .Select(...).ToArray()[0] is not fixed

Author: exyi

src/Framework/Framework/Compilation/Javascript/JavascriptTranslatableMethodCollection.cs

@@ -556,32 +556,32 @@ string GetDelegateReturnTypeHash(Type type)
                 check: (method, target, arguments) => EnsureIsComparableInJavascript(method, ReflectionUtils.GetEnumerableType(arguments.First().Type).NotNull())));
 
             AddMethodTranslator(() => Enumerable.Empty<Generic.T>().ElementAt(0),
-                new GenericMethodCompiler((args, method) => BuildIndexer(args[1], args[2], method)));
+                new GenericMethodCompiler((args, method) => BuildIndexer(args[1], args[2], method).WithAnnotation(ResultMayBeObservableAnnotation.Instance)));
             AddMethodTranslator(() => Enumerable.Empty<Generic.T>().ElementAtOrDefault(0),
-                new GenericMethodCompiler((args, method) => BuildIndexer(args[1], args[2], method)));
+                new GenericMethodCompiler((args, method) => BuildIndexer(args[1], args[2], method).WithAnnotation(ResultMayBeObservableAnnotation.Instance)));
             AddMethodTranslator(() => ImmutableArrayExtensions.ElementAt(default(ImmutableArray<Generic.T>), 0),
-                new GenericMethodCompiler((args, method) => BuildIndexer(args[1], args[2], method)));
+                new GenericMethodCompiler((args, method) => BuildIndexer(args[1], args[2], method).WithAnnotation(ResultMayBeObservableAnnotation.Instance)));
             AddMethodTranslator(() => ImmutableArrayExtensions.ElementAtOrDefault(default(ImmutableArray<Generic.T>), 0),
-                new GenericMethodCompiler((args, method) => BuildIndexer(args[1], args[2], method)));
+                new GenericMethodCompiler((args, method) => BuildIndexer(args[1], args[2], method).WithAnnotation(ResultMayBeObservableAnnotation.Instance)));
 
-            var firstOrDefault = new GenericMethodCompiler((args, m) => BuildIndexer(args[1], new JsLiteral(0), m).WithAnnotation(MayBeNullAnnotation.Instance));
+            var firstOrDefault = new GenericMethodCompiler((args, m) => BuildIndexer(args[1], new JsLiteral(0), m).WithAnnotation(MayBeNullAnnotation.Instance).WithAnnotation(ResultMayBeObservableAnnotation.Instance));
             AddMethodTranslator(() => Enumerable.Empty<Generic.T>().FirstOrDefault(), firstOrDefault);
             AddMethodTranslator(() => Enumerable.Empty<Generic.T>().First(), firstOrDefault);
             AddMethodTranslator(() => ImmutableArrayExtensions.FirstOrDefault(default(ImmutableArray<Generic.T>)), firstOrDefault);
             AddMethodTranslator(() => ImmutableArrayExtensions.First(default(ImmutableArray<Generic.T>)), firstOrDefault);
 
             var firstOrDefaultPred = new GenericMethodCompiler(args =>
-                args[1].Member("find").Invoke(args[2]).WithAnnotation(MayBeNullAnnotation.Instance));
+                args[1].Member("find").Invoke(args[2]).WithAnnotation(MayBeNullAnnotation.Instance).WithAnnotation(ResultMayBeObservableAnnotation.Instance));
             AddMethodTranslator(() => Enumerable.Empty<Generic.T>().FirstOrDefault(_ => true), firstOrDefaultPred);
             AddMethodTranslator(() => Enumerable.Empty<Generic.T>().First(_ => true), firstOrDefaultPred);
             AddMethodTranslator(() => ImmutableArrayExtensions.FirstOrDefault(default(ImmutableArray<Generic.T>), _ => true), firstOrDefaultPred);
             AddMethodTranslator(() => ImmutableArrayExtensions.First(default(ImmutableArray<Generic.T>), _ => true), firstOrDefaultPred);
 
-            var lastOrDefault = new GenericMethodCompiler(args => args[1].Member("at").Invoke(new JsLiteral(-1)).WithAnnotation(MayBeNullAnnotation.Instance));
+            var lastOrDefault = new GenericMethodCompiler(args => args[1].Member("at").Invoke(new JsLiteral(-1)).WithAnnotation(MayBeNullAnnotation.Instance).WithAnnotation(ResultMayBeObservableAnnotation.Instance));
             AddMethodTranslator(() => Enumerable.Empty<Generic.T>().LastOrDefault(), lastOrDefault);
             AddMethodTranslator(() => ImmutableArrayExtensions.LastOrDefault(default(ImmutableArray<Generic.T>)), lastOrDefault);
             var lastOrDefaultPred = new GenericMethodCompiler(args =>
-                args[1].Member("findLast").Invoke(args[2]).WithAnnotation(MayBeNullAnnotation.Instance));
+                args[1].Member("findLast").Invoke(args[2]).WithAnnotation(MayBeNullAnnotation.Instance).WithAnnotation(ResultMayBeObservableAnnotation.Instance));
             AddMethodTranslator(() => Enumerable.Empty<Generic.T>().LastOrDefault(_ => false), lastOrDefaultPred);
             AddMethodTranslator(() => ImmutableArrayExtensions.LastOrDefault(default(ImmutableArray<Generic.T>), _ => false), lastOrDefaultPred);
 

src/Tests/Binding/JavascriptCompilationTests.cs

@@ -773,6 +773,13 @@ public void JsTranslator_EnumerableLastOrDefaultParametrized(string binding)
             Assert.AreEqual("LongArray().findLast((item)=>ko.unwrap(item)>0)", result);
         }
 
+        [TestMethod]
+        public void JsTranslator_EnumerableLastOrDefaultObservable()
+        {
+            var result = CompileBinding("LongArray.LastOrDefault()==1", new[] { new NamespaceImport("System.Linq"), new NamespaceImport("System.Collections.Immutable") }, new[] { typeof(TestViewModel) });
+            Assert.AreEqual("ko.unwrap(LongArray().at(-1))==1", result);
+        }
+
         [TestMethod]
         [DataRow("Enumerable.Distinct(VmArray)", DisplayName = "Regular call of Enumerable.Distinct")]
         [DataRow("VmArray.Distinct()", DisplayName = "Syntax sugar - extension method")]

src/Tests/Binding/StaticCommandCompilationTests.cs

@@ -369,7 +369,7 @@ public void StaticCommandCompilation_LinqTranslations()
             Console.WriteLine(result);
             var expectedResult = @"{
  	let vm = options.viewModel;
- 	vm.StringProp(vm.VmArray.state.filter((x) => ko.unwrap(x).ChildObject.SomeString == ""x"")[0].SomeString);
+ 	vm.StringProp(ko.unwrap(vm.VmArray.state.filter((x) => ko.unwrap(x).ChildObject.SomeString == ""x"")[0]).SomeString);
  }";
 
             AreEqual(expectedResult, result);