I tracked this down.

panic: GetFile on  /tmp/scratch/case-insensitive import collision
golang.org/x/tools/internal/lsp/cache.(*snapshot).GetFile
golang.org/x/tools/internal/lsp/source.clearReports
golang.org/x/tools/internal/lsp/source.Diagnostics
golang.org/x/tools/internal/lsp.(*Server).diagnose.func2

clearReports probably shouldn't register a file that doesn't already exist, and we should ideally not treat case-insensitive import collision: "example.com/foo/x" and "example.com/Foo/x" as an error in the file "case-insensitive import collision".

Ah, thanks for tracking this down. I was probably too ambitious when I removed "FindFile" from the snapshot. Do you have a good sense of how we could write a regtest for this? I guess we would have to check on the condition of no diagnostics for "case-insensitive import collision"?

Are you more worried about the gratuitous Loads or the fact that the diagnostic got swallowed? I don't know how to write a test for the former, but the latter should be easy.

Really the former, but I think the latter could account for both? I'll try to figure out a good regtest for this. I can have a fix out for this soon - unless you already have one?

Change https://golang.org/cl/230315 mentions this issue: internal/lsp: make sure diagnostics only refer to exisiting files