Why SwaggerGen won't have any API info if dont execute app.Run

[ldsenow]

I am trying to use the SwaggerGenerator to export the swagger.json file. I follow how the cli does.

public static void ExportSwaggerJsonFile(this WebApplication app, string outputFilePath)
 {
            var swaggerProvider = app.Services.GetRequiredService<ISwaggerProvider>();
            var swagger = swaggerProvider.GetSwagger(app.Environment.ApplicationName);

            var s = swagger.Paths;

            var outputPath = Path.Combine(Directory.GetCurrentDirectory(), outputFilePath);

            FileInfo fi = new(outputPath);
            fi.Directory?.Create();

            using var streamWriter = File.CreateText(outputPath);
            IOpenApiWriter writer = new OpenApiJsonWriter(streamWriter);

            swagger.SerializeAsV3(writer);

            Console.WriteLine($"Swagger JSON/YAML successfully written to {outputPath}");
}

However, if I dont run the app.Run or app.Start or execute the function before the app.Run or app.Start, the output file wont contain the paths and schemas etc.

Is there a particular reason that we have to start server? We cant generate the json file based on the metadata? Or am i missing something? Any help is much appreciated.

BTW, i am on .net 6 and using swashbuckle 6.4.

[martincostello]

Duplicate of #2774

[remcolam]

@ldsenow Check also #2668, that might provide a solution for you. It should be in the next release