codeql cache

[GrosQuildu]

Update CodeQL chapter with warning to remove build caches before compiling databases. This is often a pain to discover CodeQL didn't pick up all files because of the cache.

[mschwager]

Is this for building queries or code? If you're creating the DB, then you should be able to pass --cache-cleanup=clear to database create, and if you're running queries you should be able to pass --rerun to database analyze.

Forgetting --rerun has bitten me many time 😆

[GrosQuildu]

It's about build tool cache. Like if you run make and then codeql database create, some code won't be recompiled aka won't be seen by codeql. You have to run make clean before codeql.

But we could/should mention these two flags too.