x/tools/gopls: support case insensitive file systems

[stamblerre]

gopls doesn't support case-insensitive file systems. VS Code always sends lower-case drive letters, but if a user sets their GOPATH to C://bob/go, go list will return upper-case drive letters. At that point, gopls will think it did not get metadata for the given file, and it will not work correctly.

[gopherbot]

Change https://golang.org/cl/217080 mentions this issue: internal/span: always uppercase the drive letter for Windows

[gopherbot]

Change https://golang.org/cl/217088 mentions this issue: internal/span: always uppercase the drive letter for Windows

[stamblerre]

@heschik: Do you think there is anything else we can do here to handle case insensitive file systems, or can we close this issue?

[heschi]

There might be other stuff we can do but in general I would hope that everything would be case-preserving and it wouldn't matter. I say close.

[heschi]

We have a report on Slack of VS Code using the wrong case for initialize and other file URIs, so I guess our work here is not done.

[jameshartig]

As I mentioned in Slack, I'm not sure if this is a VSCode or gopls issue. Somehow VSCode opened the folder c:\Users\James\Dropbox\go\src\gerrit.levenlabs.com\subscriber-api but the actual folder is c:\Users\james\Dropbox\go\src\gerrit.levenlabs.com\subscriber-api (notice james not James) and I think that was the root of the issue.

[Trace - 16:23:24.490 PM] Sending request 'initialize - (0)'.
Params: {"processId":15380,"rootPath":"c:\\Users\\James\\Dropbox\\go\\src\\gerrit.levenlabs.com\\subscriber-api","rootUri":"file:///c%3A/Users/James/Dropbox/go/src/gerrit.levenlabs.com/subscriber-api","capabilities":{"workspace":{"applyEdit":true,"workspaceEdit":{"documentChanges":true,"resourceOperations":["create","rename","delete"],"failureHandling":"textOnlyTransactional"},"didChangeConfiguration":{"dynamicRegistration":true},"didChangeWatchedFiles":{"dynamicRegistration":true},"symbol":{"dynamicRegistration":true,"symbolKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]}},"executeCommand":{"dynamicRegistration":true},"configuration":true,"workspaceFolders":true},"textDocument":{"publishDiagnostics":{"relatedInformation":true},"synchronization":{"dynamicRegistration":true,"willSave":true,"willSaveWaitUntil":true,"didSave":true},"completion":{"dynamicRegistration":true,"contextSupport":true,"completionItem":{"snippetSupport":true,"commitCharactersSupport":true,"documentationFormat":["markdown","plaintext"],"deprecatedSupport":true,"preselectSupport":true},"completionItemKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]}},"hover":{"dynamicRegistration":true,"contentFormat":["markdown","plaintext"]},"signatureHelp":{"dynamicRegistration":true,"signatureInformation":{"documentationFormat":["markdown","plaintext"],"parameterInformation":{"labelOffsetSupport":true}}},"definition":{"dynamicRegistration":true,"linkSupport":true},"references":{"dynamicRegistration":true},"documentHighlight":{"dynamicRegistration":true},"documentSymbol":{"dynamicRegistration":true,"symbolKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]},"hierarchicalDocumentSymbolSupport":true},"codeAction":{"dynamicRegistration":true,"codeActionLiteralSupport":{"codeActionKind":{"valueSet":["","quickfix","refactor","refactor.extract","refactor.inline","refactor.rewrite","source","source.organizeImports"]}}},"codeLens":{"dynamicRegistration":true},"formatting":{"dynamicRegistration":true},"rangeFormatting":{"dynamicRegistration":true},"onTypeFormatting":{"dynamicRegistration":true},"rename":{"dynamicRegistration":true,"prepareSupport":true},"documentLink":{"dynamicRegistration":true},"typeDefinition":{"dynamicRegistration":true,"linkSupport":true},"implementation":{"dynamicRegistration":true,"linkSupport":true},"colorProvider":{"dynamicRegistration":true},"foldingRange":{"dynamicRegistration":true,"rangeLimit":5000,"lineFoldingOnly":true},"declaration":{"dynamicRegistration":true,"linkSupport":true}}},"initializationOptions":{},"trace":"off","workspaceFolders":[{"uri":"file:///c%3A/Users/James/Dropbox/go/src/gerrit.levenlabs.com/subscriber-api","name":"subscriber-api"}]}