x/tools/gopls: panic closing overlay file

[muirdm]

I saw this panic when creating an overlay package, and then closing the buffer without ever having saved the file:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x1699ce7]

goroutine 32949 [running]:
golang.org/x/tools/internal/lsp/cache.(*snapshot).CheckPackageHandles(0xc016582370, 0x19a5c40, 0xc01b3a6b40, 0x0, 0x0, 0x1e833a0, 0x18621d3, 0x7, 0x1995240, 0xc023ef6990)
	/Users/muir/projects/tools/internal/lsp/cache/gofile.go:31 +0x37
golang.org/x/tools/internal/lsp/cache.(*view).CheckPackageHandles(0xc000316480, 0x19a5c40, 0xc01b3a6b40, 0x0, 0x0, 0xc023ef6990, 0xc006155ad0, 0x1, 0x1, 0x0, ...)
	/Users/muir/projects/tools/internal/lsp/cache/gofile.go:20 +0x76
golang.org/x/tools/internal/lsp.(*Server).didClose(0xc000259b00, 0x19a5b80, 0xc02389d2c0, 0xc00dd3bab0, 0x0, 0x0)
	/Users/muir/projects/tools/internal/lsp/text_synchronization.go:159 +0x382
golang.org/x/tools/internal/lsp.(*Server).DidClose(0xc000259b00, 0x19a5b80, 0xc02389d2c0, 0xc00dd3bab0, 0xc00dd3bab0, 0x0)
	/Users/muir/projects/tools/internal/lsp/server.go:155 +0x49
golang.org/x/tools/internal/lsp/protocol.serverHandler.Deliver(0x19bbe80, 0xc000259b00, 0x19a5b80, 0xc02389d2c0, 0xc02389d300, 0x1007000, 0xc00a0f0001)
	/Users/muir/projects/tools/internal/lsp/protocol/tsserver.go:131 +0x15e1
golang.org/x/tools/internal/jsonrpc2.(*Conn).Run.func1(0xc019660660, 0xc02389d300, 0xc000259b60, 0x19a5b80, 0xc02389d2c0, 0x0, 0x0, 0xc028f7f350)
	/Users/muir/projects/tools/internal/jsonrpc2/jsonrpc2.go:370 +0x170
created by golang.org/x/tools/internal/jsonrpc2.(*Conn).Run
	/Users/muir/projects/tools/internal/jsonrpc2/jsonrpc2.go:354 +0x877

[gopherbot]

Thank you for filing a gopls issue! Please take a look at the Troubleshooting guide, and make sure that you have provided all of the relevant information here.

[gopherbot]

Change https://golang.org/cl/204823 mentions this issue: internal/lsp: fix nil pointer in textDocument/didClose