feat(lsp): user-specified sorting of lsp.completion multi-server results #36401

Problem: No way to customize completion order across multiple servers.

Solution: Add `cmp` function to `vim.lsp.completion.enable()` options
for custom sorting logic.

runtime/doc/lsp.txt

@@ -2040,6 +2040,8 @@ enable({enable}, {client_id}, {bufnr}, {opts})
                        `triggerCharacters`.
                      • {convert}? (`fun(item: lsp.CompletionItem): table`)
                        Transforms an LSP CompletionItem to |complete-items|.
+                     • {cmp}? (`fun(a: table, b: table): boolean`) Comparator
+                       for sorting merged completion items from all servers.
 
 get({opts})                                         *vim.lsp.completion.get()*
     Triggers LSP completion once in the current buffer, if LSP completion is

runtime/doc/news.txt

@@ -264,6 +264,7 @@ LSP
 • The filter option of |vim.lsp.buf.code_action()| now receives the client ID as an argument.
 • |Client:stop()| now accepts a numerical `force` argument to be interpreted as the time to wait
   before forcing the shutdown.
+• Add cmp field to opts of |vim.lsp.completion.enable()| for custom completion ordering.
 
 LUA
 

runtime/lua/vim/lsp/completion.lua

@@ -313,6 +313,7 @@ function M._lsp_to_complete_items(result, prefix, client_id)
   local candidates = {}
   local bufnr = api.nvim_get_current_buf()
   local user_convert = vim.tbl_get(buf_handles, bufnr, 'convert')
+  local user_cmp = vim.tbl_get(buf_handles, bufnr, 'cmp')
   for _, item in ipairs(items) do
     if matches(item) then
       local word = get_completion_word(item, prefix, match_item_by_value)
@@ -348,15 +349,16 @@ function M._lsp_to_complete_items(result, prefix, client_id)
       table.insert(candidates, completion_item)
     end
   end
-  ---@diagnostic disable-next-line: no-unknown
-  table.sort(candidates, function(a, b)
-    ---@type lsp.CompletionItem
-    local itema = a.user_data.nvim.lsp.completion_item
-    ---@type lsp.CompletionItem
-    local itemb = b.user_data.nvim.lsp.completion_item
-    return (itema.sortText or itema.label) < (itemb.sortText or itemb.label)
-  end)
-
+  if not user_cmp then
+    ---@diagnostic disable-next-line: no-unknown
+    table.sort(candidates, function(a, b)
+      ---@type lsp.CompletionItem
+      local itema = a.user_data.nvim.lsp.completion_item
+      ---@type lsp.CompletionItem
+      local itemb = b.user_data.nvim.lsp.completion_item
+      return (itema.sortText or itema.label) < (itemb.sortText or itemb.label)
+    end)
+  end
   return candidates
 end
 
@@ -551,6 +553,10 @@ local function trigger(bufnr, clients, ctx)
     end, prev_matches)
 
     matches = vim.list_extend(prev_matches, matches)
+    local user_cmp = vim.tbl_get(buf_handles, bufnr, 'cmp')
+    if user_cmp then
+      table.sort(matches, user_cmp)
+    end
 
     local start_col = (server_start_boundary or word_boundary) + 1
     Context.cursor = { cursor_row, start_col }
@@ -712,6 +718,7 @@ end
 --- @class vim.lsp.completion.BufferOpts
 --- @field autotrigger? boolean  (default: false) When true, completion triggers automatically based on the server's `triggerCharacters`.
 --- @field convert? fun(item: lsp.CompletionItem): table Transforms an LSP CompletionItem to |complete-items|.
+--- @field cmp? fun(a: table, b: table): boolean Comparator for sorting merged completion items from all servers.
 
 ---@param client_id integer
 ---@param bufnr integer
@@ -719,7 +726,7 @@ end
 local function enable_completions(client_id, bufnr, opts)
   local buf_handle = buf_handles[bufnr]
   if not buf_handle then
-    buf_handle = { clients = {}, triggers = {}, convert = opts.convert }
+    buf_handle = { clients = {}, triggers = {}, convert = opts.convert, cmp = opts.cmp }
     buf_handles[bufnr] = buf_handle
 
     -- Attach to buffer events.

test/functional/plugin/lsp/completion_spec.lua

@@ -810,7 +810,7 @@ end)
 
 --- @param name string
 --- @param completion_result lsp.CompletionList
---- @param opts? {trigger_chars?: string[], resolve_result?: lsp.CompletionItem, delay?: integer}
+--- @param opts? {trigger_chars?: string[], resolve_result?: lsp.CompletionItem, delay?: integer, cmp?: string}
 --- @return integer
 local function create_server(name, completion_result, opts)
   opts = opts or {}
@@ -841,6 +841,10 @@ local function create_server(name, completion_result, opts)
 
     local bufnr = vim.api.nvim_get_current_buf()
     vim.api.nvim_win_set_buf(0, bufnr)
+    local cmp_fn
+    if opts.cmp then
+      cmp_fn = assert(loadstring(opts.cmp))
+    end
     return vim.lsp.start({
       name = name,
       cmd = server.cmd,
@@ -850,6 +854,7 @@ local function create_server(name, completion_result, opts)
           convert = function(item)
             return { abbr = item.label:gsub('%b()', '') }
           end,
+          cmp = cmp_fn,
         })
       end,
     })
@@ -1190,6 +1195,29 @@ describe('vim.lsp.completion: protocol', function()
     end)
   end)
 
+  it('enable(…,{cmp=fn}) custom sort order', function()
+    create_server('dummy', {
+      isIncomplete = false,
+      items = {
+        { label = 'zzz', sortText = 'a' },
+        { label = 'aaa', sortText = 'z' },
+        { label = 'mmm', sortText = 'm' },
+      },
+    }, {
+      cmp = string.dump(function(a, b)
+        return a.abbr < b.abbr
+      end),
+    })
+    feed('i')
+    trigger_at_pos({ 1, 0 })
+    assert_matches(function(matches)
+      eq(3, #matches)
+      eq('aaa', matches[1].abbr)
+      eq('mmm', matches[2].abbr)
+      eq('zzz', matches[3].abbr)
+    end)
+  end)
+
   it('sends completion context when invoked', function()
     local params = exec_lua(function()
       local params