How to send errors from Neovim LSP to ALE - neovim

Question

ALE has an API for sending errors to it from other sources. I'm using this like shown below and it works for the first error. More specifically, if I make one edit that results in an LSP error, the error will be displayed by ALE in the location list. If I make any further keystrokes, the location list is emptied again.
I can also trigger this behavior if I disable LSP, load ALE, manually call ShowResults and then press any other key in insert mode.
My hypothesis is that ALEs linting in insert mode (per default) kicks in. If LSP is disabled and there are no linters registered for the current file type, it doesn't find any errors (obviously, there's nothing that could report any) and so it empties my location list again. So the steps are: open buffer without LSP, call ShowResults, location list opens, press i, press any key, location list is empty
Now I thought that it was because I wasn't implementing the full ALE API. So I added a hook (2nd snippet). I can verify that this hook is called and that it generates valid messages. If I keep the location list open I can even see all the expected errors flickering across the loclist. I can navigate to those errors with :lolder, but I don't know why ALE always adds another, empty location list, after the LSP is done doing its job.
Or maybe I'm doing something wrong here.
vim.lsp.handlers["textDocument/publishDiagnostics"] = function(_, _, params, client_id, _, config)
local uri = params.uri
local bufnr = vim.uri_to_bufnr(uri)
if not bufnr then
return
end
local diagnostics = params.diagnostics
if not diagnostics or vim.tbl_isempty(diagnostics) then
vim.fn['ale#other_source#ShowResults'](bufnr, "nvim-lsp", {})
return
end
-- Important so we can pull diagnostics from this table when ALE asks for
-- them
vim.lsp.diagnostic.save(diagnostics, bufnr, client_id)
local messages = {}
for _, event in ipairs(diagnostics) do
-- :h ale-localist-format
local msg = {}
msg.text = event.message
msg.lnum = event.range.start.line
msg.end_lnum = event.range["end"].line
msg.col = event.range.start.character
msg.end_col = event.range["end"].character
msg.bufnr = bufnr
msg.nr = event.severity
table.insert(messages, msg)
end
vim.fn['ale#other_source#ShowResults'](bufnr, "nvim-lsp", messages)
end
Second snippet which is called from the 'on_attach' function of the Neovim LSP
function ALEHook(bufnr)
vim.fn['ale#other_source#StartChecking'](bufnr, "nvim-lsp")
local diagnostics = vim.lsp.diagnostic.get(bufnr, client.id)
if not diagnostics or vim.tbl_isempty(diagnostics) then
vim.fn['ale#other_source#ShowResults'](bufnr, "nvim-lsp", {})
return
end
local messages = {}
for _, event in ipairs(diagnostics) do
local msg = {}
msg.text = event.message
msg.lnum = event.range.start.line
msg.end_lnum = event.range["end"].line
msg.col = event.range.start.character
msg.end_col = event.range["end"].character
msg.bufnr = bufnr
msg.nr = event.severity
table.insert(messages, msg)
end
vim.fn['ale#other_source#ShowResults'](bufnr, "nvim-lsp", messages)
end
api.nvim_command('augroup ALEHookLSP')
api.nvim_command('autocmd!')
api.nvim_command('autocmd User ALEWantResults call v:lua.ALEHook(g:ale_want_results_buffer)')
api.nvim_command('augroup END')