Project no longer compiles after adding header file

[forsetti]

So I added a header files folder to my project and then added a header file. The project would no longer compile after doing so. To troubleshoot, I changed everything in my project back but I am getting compile errors there now too. I've verified that I have the include paths correct for all the below undefined references and if I remove those I get different errors. Any suggestions would be greatly appreciated.

Building ‘TagIt’ from solution ‘TagIt’ in configuration ‘Debug’
  Compiling ‘main.c’
  Linking TagIt.elf
    Output/TagIt Debug/Obj/main.o: In function `sara_recv_event_handler':
    undefined reference to `app_uart_get'
    Output/TagIt Debug/Obj/main.o: In function `init_sara_com':
    undefined reference to `app_uart_init'
    undefined reference to `app_uart_flush'
    Output/TagIt Debug/Obj/main.o: In function `init_pins':
    undefined reference to `nrfx_gpiote_init'
    undefined reference to `nrfx_gpiote_out_init'
    undefined reference to `nrfx_gpiote_out_init'
Build failed

[Nguyen Hoan Hoang]

You need to add the source files the .c files to the project

[forsetti]

The only source file is main.c. The project compiled previously and only failed after I attempted to add my own header file. Nothing else in the project changed.

[Nguyen Hoan Hoang]

I am surprised that you can compile before but you need to add all the missing one into the project.

[forsetti]

So I added app_uart.c and supporting files to the project and I still get the same errors.

[Nguyen Hoan Hoang]

You also need to enable whatever you need to use in the sdk_config.h to enable compilation of the source code

[forsetti]

I cannot find where in the sdk_config where APP_UART can be enabled.