internal/lsp: error handling

[mbana]

Main change is to the File interface found in internal/lsp/source/view.go.

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Patch Set 1:

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[mattn]

This file is not needed.

[mattn]

ditto

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Message from Ian Cottrell:

Patch Set 7:

I just (last week) removed all the error return values from File accessors, as I think they are the wrong choice.
See https://go-review.googlesource.com/c/tools/+/162399
Happy to have a conversation about it if you like.

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Message from Yudai Iwasaki:

Patch Set 7:

Patch Set 7:

I just (last week) removed all the error return values from File accessors, as I think they are the wrong choice.
See https://go-review.googlesource.com/c/tools/+/162399
Happy to have a conversation about it if you like.

By the way, the previous commit broke gopls because there are some code that doesn't expect nil from those File functions. gopls now panics due to nil returned by GetPackage().
(since the change was intentional, we should fix diagnostics.go?)

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x50 pc=0x6e88ed]

goroutine 21 [running]:
golang.org/x/tools/internal/lsp/source.Diagnostics(0x8b54c0, 0xc00009e010, 0x8b5600, 0xc0000ba120, 0xc00008a360, 0x57, 0xc00004e740, 0x1, 0x5d785e)
/home/yudai/gopath/src/golang.org/x/tools/internal/lsp/source/diagnostics.go:56 +0xcd
golang.org/x/tools/internal/lsp.(*server).cacheAndDiagnose.func1(0x8b54c0, 0xc00009e010, 0xc0000a7000, 0xc00008a360, 0x57)
/home/yudai/gopath/src/golang.org/x/tools/internal/lsp/diagnostics.go:24 +0x81
created by golang.org/x/tools/internal/lsp.(*server).cacheAndDiagnose
/home/yudai/gopath/src/golang.org/x/tools/internal/lsp/diagnostics.go:23 +0x13c

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