LSP config for HLS

lsp.lua

local lsp = require 'lspconfig'
local tb = require 'telescope.builtin'

local setup_diagnostics = function()
  local ns = vim.api.nvim_create_namespace('severe-diagnostics')

  -- reference to the original handler
  local orig_signs_handler = vim.diagnostic.handlers.signs

  ---Overriden diagnostics signs helper to only show the single most relevant sign
  ---@see `:h diagnostic-handlers`
  vim.diagnostic.handlers.signs = {
    show = function(_, bufnr, _, opts)
      -- get all diagnostics from the whole buffer rather
      -- than just the diagnostics passed to the handler
      local diagnostics = vim.diagnostic.get(bufnr)

        local max_severity_per_line = {}
        for _, d in pairs(diagnostics) do
          local m = max_severity_per_line[d.lnum]
          if not m or d.severity < m.severity then
            max_severity_per_line[d.lnum] = d
          end
        end

        -- Pass the filtered diagnostics (with our custom namespace) to
        -- the original handler
      local filtered_diagnostics = vim.tbl_values(max_severity_per_line)

      local success, result = pcall(function()
        -- pass the filtered diagnostics (with the
        -- custom namespace) to the original handler
        orig_signs_handler.show(ns, bufnr, filtered_diagnostics, opts)
      end)

      if not success then
        print(ns, bufnr, vim.inspect(filtered_diagnostics), vim.inspect(opts), 'Showing max diagnostic failed', result)
      end
    end,

    hide = function(_, bufnr)
      orig_signs_handler.hide(ns, bufnr)
    end,
  }
end


local keymap = vim.keymap.set
local def_opts = { noremap = true, silent = true, }

local on_attach = function(client, bufnr)
  -- Enable completion triggered by <c-x><c-o>
  vim.api.nvim_buf_set_option(bufnr, 'omnifunc', 'v:lua.vim.lsp.omnifunc')

  local bufopts = vim.tbl_extend('keep', def_opts, { buffer = bufnr })
  keymap('n', 'K', vim.lsp.buf.hover, bufopts)
  keymap('n', '<leader>k', vim.diagnostic.open_float, bufopts)
  keymap('n', 'gd', tb.lsp_definitions, bufopts)
  keymap('n', '<leader>go', tb.lsp_outgoing_calls, bufopts)
  keymap('n', '<leader>gi', tb.lsp_incoming_calls, bufopts)
  keymap('n', '<leader>ac', vim.lsp.buf.code_action, bufopts)
  keymap('n', '<leader>la', vim.lsp.codelens.run, bufopts)
  keymap('n', '<leader>rn', vim.lsp.buf.rename, bufopts)
  keymap('n', '<leader>F', function() vim.lsp.buf.format {async = true} end, bufopts)
  keymap('v', '<leader>F', vim.lsp.buf.format, bufopts)
  keymap('n', '<leader>ls', tb.lsp_document_symbols, bufopts)
  keymap('n', '<leader>lw', tb.lsp_workspace_symbols, bufopts)
  keymap('n', '<leader>lq', tb.lsp_dynamic_workspace_symbols, bufopts)
  keymap('n', '<leader>rf', tb.lsp_references, bufopts)
  keymap('n', '<leader>dn', vim.diagnostic.goto_next, bufopts)
  keymap('n', '<leader>dp', vim.diagnostic.goto_prev, bufopts)
  keymap('n', '<leader>lo', '<cmd>:SymbolsOutline<CR>', bufopts)

end

local capabilities = require('cmp_nvim_lsp').default_capabilities()

-- Haskell language server via haskell-tools
vim.g.haskell_tools = {
  tools = {
    hover = { enable = false }
  },
  hls = {
    on_attach = function(client, bufnr, ht)
      on_attach(client, bufnr)
      local bufopts = vim.tbl_extend('keep', def_opts, { buffer = bufnr, })
      keymap('n', '<leader>hs', ht.hoogle.hoogle_signature, bufopts)
      -- Toggle a GHCi repl for the current package
      keymap('n', '<leader>rp', ht.repl.toggle, bufopts)
      -- Toggle a GHCi repl for the current buffer
      keymap('n', '<leader>rb', function()
        ht.repl.toggle(vim.api.nvim_buf_get_name(0))
      end, bufopts)
      keymap('n', '<leader>rq', ht.repl.quit, bufopts)
    end,
    default_settings = {
      -- project checking leads to poor performance on large projects
      -- checkProject = false,
    }
  }
}

local signs = { Error = ' ', Warn = ' ', Hint = ' ', Info = ' ' }
for type, icon in pairs(signs) do
  local hl = 'DiagnosticSign' .. type
  vim.fn.sign_define(hl, { text = icon, texthl = hl, numhl = hl })
end

vim.cmd[[ hi link LspCodeLens FloatBorder ]]

-- display only one sign with the highest severity
setup_diagnostics()