Improve support for methods with multiple JSInvokable attributes (#59787)

* * Improve support for methods with multiple JSInvokable
* Add tests.

* * Improve support for methods with multiple JSInvokable
* Add tests.

Author: rsandbach

src/JSInterop/Microsoft.JSInterop/src/Infrastructure/DotNetDispatcher.cs

@@ -407,18 +407,21 @@ private static (MethodInfo methodInfo, Type[] parameterTypes) GetCachedMethodInf
                     continue;
                 }
 
-                var identifier = method.GetCustomAttribute<JSInvokableAttribute>(false)!.Identifier ?? method.Name!;
-                var parameterTypes = GetParameterTypes(method);
-
-                if (result.ContainsKey(identifier))
+                foreach (var attr in method.GetCustomAttributes<JSInvokableAttribute>(false))
                 {
-                    throw new InvalidOperationException($"The type {type.Name} contains more than one " +
-                        $"[JSInvokable] method with identifier '{identifier}'. All [JSInvokable] methods within the same " +
-                        "type must have different identifiers. You can pass a custom identifier as a parameter to " +
-                        $"the [JSInvokable] attribute.");
+                    var identifier = attr.Identifier ?? method.Name;
+                    var parameterTypes = GetParameterTypes(method);
+
+                    if (result.ContainsKey(identifier))
+                    {
+                        throw new InvalidOperationException($"The type {type.Name} contains more than one " +
+                            $"[JSInvokable] method with identifier '{identifier}'. All [JSInvokable] methods within the same " +
+                            "type must have different identifiers. You can pass a custom identifier as a parameter to " +
+                            $"the [JSInvokable] attribute.");
+                    }
+
+                    result.Add(identifier, (method, parameterTypes));
                 }
-
-                result.Add(identifier, (method, parameterTypes));
             }
 
             return result;
@@ -443,18 +446,21 @@ private static (MethodInfo methodInfo, Type[] parameterTypes) GetCachedMethodInf
                     continue;
                 }
 
-                var identifier = method.GetCustomAttribute<JSInvokableAttribute>(false)!.Identifier ?? method.Name;
-                var parameterTypes = GetParameterTypes(method);
-
-                if (result.ContainsKey(identifier))
+                foreach (var attr in method.GetCustomAttributes<JSInvokableAttribute>(false))
                 {
-                    throw new InvalidOperationException($"The assembly '{assemblyKey.AssemblyName}' contains more than one " +
-                        $"[JSInvokable] method with identifier '{identifier}'. All [JSInvokable] methods within the same " +
-                        $"assembly must have different identifiers. You can pass a custom identifier as a parameter to " +
-                        $"the [JSInvokable] attribute.");
+                    var identifier = attr.Identifier ?? method.Name;
+                    var parameterTypes = GetParameterTypes(method);
+
+                    if (result.ContainsKey(identifier))
+                    {
+                        throw new InvalidOperationException($"The assembly '{assemblyKey.AssemblyName}' contains more than one " +
+                            $"[JSInvokable] method with identifier '{identifier}'. All [JSInvokable] methods within the same " +
+                            $"assembly must have different identifiers. You can pass a custom identifier as a parameter to " +
+                            $"the [JSInvokable] attribute.");
+                    }
+
+                    result.Add(identifier, (method, parameterTypes));
                 }
-
-                result.Add(identifier, (method, parameterTypes));
             }
         }
 

src/JSInterop/Microsoft.JSInterop/test/Infrastructure/DotNetDispatcherTest.cs

@@ -496,6 +496,42 @@ public void CanInvokeMethodsThatAcceptGenericParametersOnGenericTypes()
         Assert.Equal("\"hello world\"", resultJson);
     }
 
+    
+    [Fact]
+    public void CanInvokeMethodsWithMultipleIdentifiers() {
+        var jsRuntime = new TestJSRuntime();
+        var targetInstance = new MultipleJSInvokableAttributes();
+        jsRuntime.Invoke<object>("_setup",
+            DotNetObjectReference.Create(targetInstance));
+        var argsJson = "[\"hello Alias\"]";
+
+        // Act
+        var resultJson = DotNetDispatcher.Invoke(jsRuntime, new DotNetInvocationInfo(null, "MultipleJSInvokableAttributesInstance", 1, default), argsJson);
+        var resultJson2 = DotNetDispatcher.Invoke(jsRuntime, new DotNetInvocationInfo(null, "Alias", 1, default), argsJson);
+
+        // Assert
+        Assert.Equal("\"hello Alias\"", resultJson);
+        Assert.Equal("\"hello Alias\"", resultJson2);
+    }
+    [Fact]
+    public void CanInvokeMethodsWithMultipleIdentifiers_Static()
+    {
+        // Arrange/Act
+        var jsRuntime = new TestJSRuntime();
+        var resultJson = DotNetDispatcher.Invoke(jsRuntime, new DotNetInvocationInfo(thisAssemblyName, "InvocableStaticNonVoidAlias1", default, default), null);
+        var result = JsonSerializer.Deserialize<TestDTO>(resultJson, jsRuntime.JsonSerializerOptions);
+
+        var resultJson2 = DotNetDispatcher.Invoke(jsRuntime, new DotNetInvocationInfo(thisAssemblyName, "InvocableStaticNonVoidAlias2", default, default), null);
+        var result2 = JsonSerializer.Deserialize<TestDTO>(resultJson2, jsRuntime.JsonSerializerOptions);
+
+        // Assert
+        Assert.Equal("Test", result.StringVal);
+        Assert.Equal(456, result.IntVal);
+
+        Assert.Equal("Test", result2.StringVal);
+        Assert.Equal(456, result2.IntVal);
+    }
+
     [Fact]
     public void CannotInvokeStaticOpenGenericMethods()
     {
@@ -874,6 +910,10 @@ public static void MyInvocableVoid()
         public static object MyInvocableNonVoid()
             => new TestDTO { StringVal = "Test", IntVal = 123 };
 
+        [JSInvokable("InvocableStaticNonVoidAlias1"), JSInvokable("InvocableStaticNonVoidAlias2")]
+        public static object MyInvocableNonVoidWithAlias()
+            => new TestDTO { StringVal = "Test", IntVal = 456 };
+
         [JSInvokable("InvocableStaticWithParams")]
         public static object[] MyInvocableWithParams(TestDTO dtoViaJson, int[] incrementAmounts, DotNetObjectReference<TestDTO> dtoByRef)
             => new object[]
@@ -1017,12 +1057,17 @@ public class GenericType<TValue>
         [JSInvokable] public TValue EchoParameter(TValue input) => input;
     }
 
+    public class MultipleJSInvokableAttributes
+    {
+        [JSInvokable, JSInvokable("Alias")] public string MultipleJSInvokableAttributesInstance(string input) => input;
+    }
+
     public class GenericMethodClass
     {
         [JSInvokable("StaticGenericMethod")] public static string StaticGenericMethod<TValue>(TValue input) => input.ToString();
         [JSInvokable("InstanceGenericMethod")] public string GenericMethod<TValue>(TValue input) => input.ToString();
     }
-
+   
     public class TestJSRuntime : JSInProcessRuntime
     {
         private TaskCompletionSource _nextInvocationTcs = new TaskCompletionSource();