Problem:
vim.lsp.tagfunc looks for the presence of 'c' (cursor) flag and issues
sync textDocument/definition requests to all clients, otherwise
workspace/symbol requests. But 'c' flag can also be set during the
insert mode completion, e.g. with an empty tag completion query, the tag
func receives pattern of '\<\k\k' with flags 'cir'.
Solution:
check for 'i' (insert mode completion) flag and don't issue any LSP
requests, return vim.NIL for immediate fallback to tags.
1629493f72