x/tools/internal/span: URI.IsFile() should support file:/absolute/path URIs

[briandealwis]

gopls v0.7.3 with Eclipse LSP4e 0.13.8 is breaking as LSP4e sends local file URIs with a single / (protocol trace below). This causes internal/span.URI.IsFile() to reject the URI as a file: URI:

func (uri URI) IsFile() bool {
    return strings.HasPrefix(string(uri), "file://")
}

and leads to gopls rejecting the workspace folder:

unsupported URI schemes: [{file:/Users/bdealwis/Projects/Skaffold/repo-skaffold skaffold}] (gopls only supports file URIs)

The file: scheme an absolute path is a permitted value under RFC8089 (The "file" URI Scheme) as the file-hier-part can be a local-path, which in turn is an path-absolute

file-URI       = file-scheme ":" file-hier-part
file-scheme    = "file"
file-hier-part = ( "//" auth-path )
                     / local-path
local-path     = path-absolute

path-absolute is referenced from RFC3986:

path-absolute = "/" [ segment-nz *( "/" segment ) ]
segment       = *pchar
segment-nz    = 1*pchar

Although the protocol trace shows Eclipse LSP4e is inconsistently using both file:/// and file:/ URIs, gopls should not reject permitted values.

And indeed Go's net/url.Parse() has tests to ensure support of file:/ URIs.

pretty-printed protocol trace

``` [t=1636554142972] LSP4E to ca.mt.gore.server: { "jsonrpc": "2.0", "id": "1", "method": "initialize", "params": { "processId": 58708, "rootPath": "/Users/bdealwis/Projects/Skaffold/repo-skaffold/", "rootUri": "file:///Users/bdealwis/Projects/Skaffold/repo-skaffold/", "initializationOptions": { "experimentalWorkspaceModule": false, "experimentalDiagnosticsDelay": "100ms", "codelenses": { "test": true } }, "capabilities": { "workspace": { "applyEdit": true, "workspaceEdit": { "documentChanges": true, "resourceOperations": [ "create", "delete", "rename" ], "failureHandling": "undo" }, "symbol": { "dynamicRegistration": true }, "executeCommand": { "dynamicRegistration": true }, "workspaceFolders": true }, "textDocument": { "synchronization": { "willSave": true, "willSaveWaitUntil": true, "didSave": true }, "completion": { "completionItem": { "snippetSupport": true, "documentationFormat": [ "markdown", "plaintext" ] } }, "hover": { "contentFormat": [ "markdown", "plaintext" ] }, "signatureHelp": {}, "references": {}, "documentHighlight": {}, "documentSymbol": { "symbolKind": { "valueSet": [18,17,5,14,9,10,22,24,8,1,12,11,20,6,2,3,21,16,19,25,4,7,15,23,26,13] }, "hierarchicalDocumentSymbolSupport": true }, "formatting": { "dynamicRegistration": true }, "rangeFormatting": {}, "definition": { "linkSupport": true }, "typeDefinition": { "linkSupport": true }, "codeAction": { "codeActionLiteralSupport": { "codeActionKind": { "valueSet": [ "quickfix", "refactor", "refactor.extract", "refactor.inline", "refactor.rewrite", "source", "source.organizeImports" ] } }, "dynamicRegistration": true }, "codeLens": {}, "documentLink": {}, "colorProvider": {}, "rename": {}, "foldingRange": {} } }, "clientName": "Eclipse IDE", "trace": "messages", "workspaceFolders": [ { "uri": "file:/Users/bdealwis/Projects/Skaffold/repo-skaffold", "name": "skaffold" } ] } } [t=1636554143277] ca.mt.gore.server to LSP4E: { "jsonrpc": "2.0", "error": { "code": 0, "message": "unsupported URI schemes: [{file:/Users/bdealwis/Projects/Skaffold/repo-skaffold skaffold}] (gopls only supports file URIs)" }, "id": "1" } ``` (`ca.mt.gore.server` is a [simple Eclipse plugin](https://github.com/briandealwis/gore) to install and configure `gopls` for Eclipse.)

[cagedmantis]

/cc @ianthehat @heschi

[heschi]

This is really part of gopls, cc @findleyr.

[briandealwis]

I've pushed a trivial patch in https://github.com/golang/tools/pull/358

[gopherbot]

Change https://golang.org/cl/376234 mentions this issue: internal/span: fix URI.IsFile() to support local-path URIs