Reset OpenApiSchemaTransformerContext before each invocation

Author: captainsafia

src/OpenApi/src/Services/Schemas/OpenApiSchemaService.cs

@@ -155,6 +155,8 @@ internal async Task ApplySchemaTransformersAsync(OpenApiSchema schema, Type type
         };
         for (var i = 0; i < _openApiOptions.SchemaTransformers.Count; i++)
         {
+            // Reset context object to base state before running each transformer.
+            context.UpdateJsonTypeInfo(jsonTypeInfo, null);
             var transformer = _openApiOptions.SchemaTransformers[i];
             // If the transformer is a type-based transformer, we need to initialize and finalize it
             // once in the context of the top-level assembly and not the child properties we are invoking

src/OpenApi/test/Transformers/SchemaTransformerTests.cs

@@ -19,7 +19,28 @@ public async Task SchemaTransformer_CanAccessTypeAndParameterDescriptionForParam
         builder.MapPost("/todo", (Todo todo) => { });
 
         var options = new OpenApiOptions();
+        var firstInvocationOnSecondTransformer = true;
         options.AddSchemaTransformer((schema, context, cancellationToken) =>
+        {
+            ValidateContext(context);
+            return Task.CompletedTask;
+        })
+        .AddSchemaTransformer((schema, context, cancellationToken) =>
+        {
+            // Coverage for https://github.com/dotnet/aspnetcore/issues/56899
+            if (firstInvocationOnSecondTransformer)
+            {
+                Assert.Equal(typeof(Todo), context.JsonTypeInfo.Type);
+                firstInvocationOnSecondTransformer = false;
+            }
+            // Rest of the state is still consistent
+            ValidateContext(context);
+            return Task.CompletedTask;
+        });
+
+        await VerifyOpenApiDocument(builder, options, document => { });
+
+        static void ValidateContext(OpenApiSchemaTransformerContext context)
         {
             if (context.JsonPropertyInfo == null)
             {
@@ -42,10 +63,7 @@ public async Task SchemaTransformer_CanAccessTypeAndParameterDescriptionForParam
             {
                 Assert.Equal(typeof(DateTime), context.JsonTypeInfo.Type);
             }
-            return Task.CompletedTask;
-        });
-
-        await VerifyOpenApiDocument(builder, options, document => { });
+        }
     }
 
     [Fact]