(mini.completion) FEATURE: Prefer completion start from LSP.

Details:
- Resolves #679.
- Resolves #306.

Author: echasnovski

Diff for: lua/mini/completion.lua

@@ -368,7 +368,7 @@ MiniCompletion.completefunc_lsp = function(findstart, base)
     if findstart == 1 then return -3 end
     return {}
   else
-    if findstart == 1 then return H.get_completion_start() end
+    if findstart == 1 then return H.get_completion_start(H.completion.lsp.result) end
 
     local process_items = H.get_config().lsp_completion.process_items
     local words = H.process_lsp_response(H.completion.lsp.result, function(response, client_id)
@@ -1285,12 +1285,29 @@ end
 
 H.pumvisible = function() return vim.fn.pumvisible() > 0 end
 
-H.get_completion_start = function()
-  -- Compute start position of latest keyword (as in `vim.lsp.omnifunc`)
+H.get_completion_start = function(lsp_result)
   local pos = vim.api.nvim_win_get_cursor(0)
+
+  -- Prefer completion start from LSP response(s)
+  for _, response_data in pairs(lsp_result or {}) do
+    local server_start = H.get_completion_start_server(response_data, pos[1] - 1)
+    if server_start ~= nil then return server_start end
+  end
+
+  -- Fall back to start position of latest keyword
   local line = vim.api.nvim_get_current_line()
-  local line_to_cursor = line:sub(1, pos[2])
-  return vim.fn.match(line_to_cursor, '\\k*$')
+  return vim.fn.match(line:sub(1, pos[2]), '\\k*$')
+end
+
+H.get_completion_start_server = function(response_data, line_num)
+  if response_data.err or type(response_data.result) ~= 'table' then return end
+  local items = response_data.result.items or response_data.result
+  for _, item in pairs(items) do
+    if type(item.textEdit) == 'table' and item.textEdit.range.start.line == line_num then
+      -- NOTE: Ignore case when items contain several conflicting starts
+      return item.textEdit.range.start.character
+    end
+  end
 end
 
 H.is_whitespace = function(s)

Diff for: tests/dir-completion/mock-months-lsp.lua

@@ -44,15 +44,29 @@ local construct_additionTextEdits = function(id, name)
   }
 end
 
+local construct_textEdit = function(name)
+  local pos = _G.mock_textEdit_pos
+  if pos == nil then return end
+  return {
+    newText = '.' .. name,
+    range = {
+      start = { line = pos[1] - 1, character = pos[2] - 1 },
+      ['end'] = { line = pos[1] - 1, character = pos[2] },
+    },
+  }
+end
+
 Months.requests = {
   ['textDocument/completion'] = function(params)
     local items = {}
     for i, item in ipairs(Months.items) do
       local res = { label = item.name, kind = item.kind, sortText = ('%03d'):format(i) }
-      -- Mock additionalTextEdits as in `pyright`
+      -- Mock `additionalTextEdits` as in `pyright`
       if vim.tbl_contains({ 'September', 'November' }, item.name) then
         res.additionalTextEdits = construct_additionTextEdits('completion', item.name)
       end
+      -- Mock `textEdit` as in `tsserver` when called after `.`
+      if vim.tbl_contains({ 'April', 'August' }, item.name) then res.textEdit = construct_textEdit(item.name) end
       table.insert(items, res)
     end
 

Diff for: tests/test_completion.lua

@@ -468,6 +468,18 @@ T['Manual completion']['applies `additionalTextEdits` from "completionItem/resol
   eq(get_lines(), { 'January' })
 end
 
+T['Manual completion']['prefers completion range from LSP response'] = function()
+  set_lines({})
+  type_keys('i', 'months.')
+  child.lua('_G.mock_textEdit_pos = vim.api.nvim_win_get_cursor(0)')
+  type_keys('<C-space>')
+
+  eq(get_completion(), { '.April', '.August' })
+  type_keys('<C-n>', '<C-y>')
+  eq(get_lines(), { 'months.April' })
+  eq(get_cursor(), { 1, 12 })
+end
+
 T['Manual completion']['respects `vim.{g,b}.minicompletion_disable`'] = new_set({
   parametrize = { { 'g' }, { 'b' } },
 }, {