Warnings can stick around even when no longer relevant.

[natefaubion]

Steps to reproduce:

• With IDE build, modify a file such that it generates a warning.
• Restore the file in a CLI, such as with git checkout.
• Do a full build in the editor.

Warnings will stick around after the full build even though the code generating the warning no longer exists, and a full build is clean. Needs a no-op save for the offending file in the editor to get it to go away.