I, too am having problems opening the serial port from Visual Studio. The problem occurs with M5Stack ESP32 device in debug mode. 

I *am* able to connect to the M5Stack ESP32 in release mode, however initially nothing ever displays; I always need to manual click "rts" to actually have serial data display.

I *am* able to connect to Adafruit Feather 32u4 in *both* debug and release modes.

My  M5Stack ESP32 (*edit2) serial port is Silicon Labs CP210x USB to UART Bridge (COM4) 11/15/2017 Version 10.1.1951

My 32u4 (*edit2) serial port simply says "USB Serial Device (COM8)" in device manager. Apparently default Microsoft drivers. 6/21/2006 (yes, '06!) Version 10.0.16299.15

*edit 2 - this may be the same issue as: http://www.visualmicro.com/forums/YaBB.pl?num=1514411767/

During debug compile-time, the ESP32 complains with:

VM_Boards.h: 653:2: error: #error "Please edit Boards.h with a hardware abstraction for this board"
   #error "Please edit Boards.h with a hardware abstraction for this board"
   for (analogPin = 0; analogPin < TOTAL_ANALOG_PINS; analogPin++)
 

and at the end:

Error compiling libraries
   Debug Build Error: This hardware might not support the default Visual Micro Debugger.
	If this project is using OTA/WiFi upload then please use the vMicro>Debugger menu to set the Serial COM and Remote port for the debugger.
	Otherwise switch the toolbar from 'Debug' to 'Release' and build again.
		or switch off Automatic Debugging
		or configure the SoftwareSerial debugger option.
Debug build failed for project 'M5StackConsole' 

curiously, I have only one Boards.h file on my entire computer, located in:

 C:\Program Files (x86)\Arduino\libraries\Firmata 

but it would seem unlikely that VisualMicro is including  this one for ESP32 or 32u4, so perhaps the proper Boards.h file is simply missing? Or a different M5Stack USB driver?

Help-About:
Microsoft Visual Studio Enterprise 2017 
Version 15.5.6
VisualStudio.15.Release/15.5.6+27130.2027
Microsoft .NET Framework
Version 4.7.02556

Visual C# 2017   00369-90250-38212-AA522
Microsoft Visual C# 2017

Visual C++ 2017   00369-90250-38212-AA522
Microsoft Visual C++ 2017

Arduino for Visual Studio   1.0

Tools-Extensions and Updates:
Arduino IDE for Visual Studio 2/10/2018 
Version 1801.27.0

*edit: added USB driver dates and version info
*edit(2): fixed mixed up USB driver text for ESP32 vs 32u4.

actually, I *was* having USB problems, but in all my fussing to get it resolved, some setting in Visual Studio must causing this error.

The problem I had with USB drivers was related to the version as noted in another thread. Setting to older CP210x driver (6.7.4.261) instead of the most recent version fixes the USB problem.

The debug compile error however... no idea. Creating a new project and copying everything seems to have resolved. I can compile and debug my ESP32 M5Stack code.

If you are interested, I save the old, problematic version here:

https://github.com/gojimmypi/LoRa-GPIO/tree/master/M5StackConsole-bad

The working version is here:

https://github.com/gojimmypi/LoRa-GPIO/tree/master/M5StackConsole

hopefully this helps before you go chasing the header def problem