Cannot open source file " literally any zephyr file"

I'm pulling my hair out here. 

Why would syntax errors completely break the toolchain?

Every now and then ill have a syntax error which causes the build to fail, the entire application corrupts and key files are then lost. 

In this state a prestine build does not work. 
undoing my changes does not work. 

Deleting the application does not work. 

Even clearing out everything, starting with a new hello world example and sterile nrf52840dk development kit build fails and key includes fail to be found.

Why would this happen?

currently no zephyr file can be found. 
I've reinstalled the toolchain. 

Previously I've had to completley uninstall vscode and reinstall nrfconnect and all the extensions. 

This is a NIGHTMARE. what is going on.

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