7966: Diagnose files that aren't in the module tree r=jonas-schievink a=jonas-schievink
Fixes https://github.com/rust-analyzer/rust-analyzer/issues/6377
I'm not sure if this is the best way to do this. It will cause false positives for all `include!`d files (though I'm not sure how much IDE functionality we have for these).
Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>
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