Please refer to https://github.com/microsoft/language-server-protocol/issues/83, https://github.com/emacs-lsp/lsp-mode/pull/1939 and https://github.com/microsoft/language-server-protocol/blob/gh-pages/_specifications/specification-3-16.md#textDocument_completion. This capability replaces `keepWhitespace`