internal/lsp: use rootURI as config.Dir in packages.Load

This change was inspired by https://golang.org/cl/153777.

Fixes golang/go#29174

Change-Id: I9d9a8b95e984c8e70160d199cd1efc5aa2964ef7
Reviewed-on: https://go-review.googlesource.com/c/153863
Reviewed-by: Ian Cottrell <iancottrell@google.com>

internal/lsp/cache/view.go

@@ -21,9 +21,10 @@ type View struct {
 	files map[source.URI]*File
 }
 
-func NewView() *View {
+func NewView(rootPath string) *View {
 	return &View{
 		Config: &packages.Config{
+			Dir:     rootPath,
 			Mode:    packages.LoadSyntax,
 			Fset:    token.NewFileSet(),
 			Tests:   true,

internal/lsp/lsp_test.go

@@ -58,7 +58,7 @@ func testLSP(t *testing.T, exporter packagestest.Exporter) {
 	defer exported.Cleanup()
 
 	s := &server{
-		view: cache.NewView(),
+		view: cache.NewView(exported.Config.Dir),
 	}
 	// Merge the exported.Config with the view.Config.
 	cfg := *exported.Config

internal/lsp/server.go

@@ -42,13 +42,18 @@ func (s *server) Initialize(ctx context.Context, params *protocol.InitializePara
 	if s.initialized {
 		return nil, jsonrpc2.NewErrorf(jsonrpc2.CodeInvalidRequest, "server already initialized")
 	}
-	s.view = cache.NewView()
 	s.initialized = true // mark server as initialized now
 
 	// Check if the client supports snippets in completion items.
 	s.snippetsSupported = params.Capabilities.TextDocument.Completion.CompletionItem.SnippetSupport
 	s.signatureHelpEnabled = true
 
+	rootPath, err := source.URI(*params.RootURI).Filename()
+	if err != nil {
+		return nil, err
+	}
+	s.view = cache.NewView(rootPath)
+
 	return &protocol.InitializeResult{
 		Capabilities: protocol.ServerCapabilities{
 			CompletionProvider: protocol.CompletionOptions{