x/tools/gopls: nil pointer deference in semanticTokensRange when viewing git diff

[zikaeroh]

ATTENTION: Please answer these questions BEFORE submitting your issue. Thanks!

What did you do?

Opened up VS Code's git diff viewer. I also run the nightly extension (which IIRC now includes semantic tokens support via an updated LSP client).

What did you expect to see?

No crash.

What did you see instead?

The server crashes with the diff open.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0xbd2631]

goroutine 124 [running]:
golang.org/x/tools/internal/lsp.(*Server).semanticTokensRange(0xc0000e0bb0, 0xef58e0, 0xc00046e500, 0xc0063d9220, 0x0, 0x0, 0xc00123c160)
	/home/jake/go/pkg/mod/golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e/internal/lsp/semantic.go:44 +0x191
golang.org/x/tools/internal/lsp.(*Server).SemanticTokensRange(0xc0000e0bb0, 0xef58e0, 0xc00046e500, 0xc0063d9220, 0xc0063d9220, 0x0, 0x0)
	/home/jake/go/pkg/mod/golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e/internal/lsp/server_gen.go:176 +0x49
golang.org/x/tools/internal/lsp/protocol.serverDispatch(0xef58e0, 0xc00046e500, 0xf09480, 0xc0000e0bb0, 0xc0063ec270, 0xef5b20, 0xc00046e480, 0x0, 0xee2e00, 0xc00123c000)
	/home/jake/go/pkg/mod/golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e/internal/lsp/protocol/tsserver.go:253 +0x5f92
golang.org/x/tools/internal/lsp/protocol.ServerHandler.func1(0xef58e0, 0xc00046e500, 0xc0063ec270, 0xef5b20, 0xc00046e480, 0x328fc423, 0x134fde0)
	/home/jake/go/pkg/mod/golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e/internal/lsp/protocol/protocol.go:63 +0xc5
golang.org/x/tools/internal/lsp/lsprpc.handshaker.func1(0xef58e0, 0xc00046e500, 0xc0063ec270, 0xef5b20, 0xc00046e480, 0x0, 0x0)
	/home/jake/go/pkg/mod/golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e/internal/lsp/lsprpc/lsprpc.go:557 +0x452
golang.org/x/tools/internal/jsonrpc2.MustReplyHandler.func1(0xef58e0, 0xc00046e500, 0xc0003e5580, 0xef5b20, 0xc00046e480, 0x0, 0x0)
	/home/jake/go/pkg/mod/golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e/internal/jsonrpc2/handler.go:35 +0xcf
golang.org/x/tools/internal/jsonrpc2.AsyncHandler.func1.2(0xc00028ed20, 0xc0004382a0, 0xc0005be3e0, 0xef58e0, 0xc00046e500, 0xc0003e5580, 0xef5b20, 0xc00046e480)
	/home/jake/go/pkg/mod/golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e/internal/jsonrpc2/handler.go:103 +0x86
created by golang.org/x/tools/internal/jsonrpc2.AsyncHandler.func1
	/home/jake/go/pkg/mod/golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e/internal/jsonrpc2/handler.go:100 +0x173
[Error - 7:24:29 PM] Connection to server got closed. Server will not be restarted.

Logs: https://gist.github.com/zikaeroh/96741da55aad5964576e0aba864cbeb3

Build info

golang.org/x/tools/gopls master
    golang.org/x/tools/gopls@v0.0.0-20201009010951-9ab7e515274e h1:Fxf8D75bsdvDgLpM6enYCHxPn+lFAiEBFAvdk/0UJ7s=
    github.com/BurntSushi/toml@v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
    github.com/google/go-cmp@v0.5.1 h1:JFrFEBb2xKufg6XkJsJr+WbKb4FQlURi5RUcBveYu9k=
    github.com/sergi/go-diff@v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
    golang.org/x/mod@v0.3.0 h1:RM4zey1++hCTbCVQfnWeKs9/IEsaBLA8vTkd0WVtmH4=
    golang.org/x/sync@v0.0.0-20200625203802-6e8e738ad208 h1:qwRHBd0NqMbJxfbotnDhm2ByMI1Shq4Y6oRJo21SGJA=
    golang.org/x/tools@v0.0.0-20201009010951-9ab7e515274e h1:x1hHgXABYbwIYbEYxs6ypae/tryqQ7YQ1/DwGyKp4Ok=
    golang.org/x/xerrors@v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
    honnef.co/go/tools@v0.0.1-2020.1.5 h1:nI5egYTGJakVyOryqLs1cQO5dO0ksin5XXs2pspk75k=
    mvdan.cc/gofumpt@v0.0.0-20200802201014-ab5a8192947d h1:t8TAw9WgTLghti7RYkpPmqk4JtQ3+wcP5GgZqgWeWLQ=
    mvdan.cc/xurls/v2@v2.2.0 h1:NSZPykBXJFCetGZykLAxaL6SIpvbVy/UFEniIfHAa8A=

[stamblerre]

/cc @pjweinb

[gopherbot]

Change https://golang.org/cl/260806 mentions this issue: internal/lsp: handle nil pointer in semantic tokens

[zikaeroh]

Note that the same thing seems to happen when you open up a go.mod file; not sure if it's the same fix or not.