lsp: Missing built-in data is not a hard error (#619)

Now when built-in state is not known for a file,
the hover response is empty. This is commonly the case
when the file that has just been opened has failed to
parse and never parsed in the time that the server has
been running.

Signed-off-by: Charlie Egan <charlie@styra.com>

internal/lsp/server.go

@@ -327,8 +327,12 @@ func (l *LanguageServer) handleHover(
 	}
 
 	builtinsOnLine, ok := l.cache.GetBuiltinPositions(params.TextDocument.URI)
+	// when no builtins are found, we can't return a useful hover response.
+	// log the error, but return an empty struct to avoid an error being shown in the client.
 	if !ok {
-		return struct{}{}, fmt.Errorf("could not get builtins for uri %q", params.TextDocument.URI)
+		l.logError(fmt.Errorf("could not get builtins for uri %q", params.TextDocument.URI))
+
+		return struct{}{}, nil
 	}
 
 	for _, bp := range builtinsOnLine[params.Position.Line+1] {