How to re-trigger all compiler warnings in the Editor??

Here's an amazingly simple thing I don't know about Unity. Open a project. In the console, you'll see 100s of WARNINGS from the compiler. (Assuming your colleagues are untidy.) Now, once you run the project, YOU DON'T SEE THOSE AGAIN. My workflow - quit Unity, delete ScriptAssemblies/, and launch again. You now get to see all the warnings again. Simply - how the hell do you properly get the warnings to "appear again" ?? Note -- ReimportAll is not practical, as it re-imports gigabytes of art assets. Cheers