Lua LSP recognizes conventional 'M' as the current module.

Completions, signature help, etc. will work inside modules.

init_test.lua

@@ -338,11 +338,38 @@ test('lua lsp should work for untitled buffers', function()
 
 	test.type('string.byte(')
 
-	lsp.stop()
 	test.assert_equal(auto_c_show.called, true)
 	test.assert_equal(call_tip_show.called, true)
 end)
 
+test('lua lsp should recognize M as the current module', function()
+	local _<close> = test.tmpfile('.lua', [[
+--- @module name
+local M = {}
+
+--- Field.
+M.field = ''
+
+--- Func.
+function M.func() end
+]], true)
+	lsp.start()
+	buffer:document_end()
+
+	local auto_c_show = test.stub()
+	local _<close> = test.mock(buffer, 'auto_c_show', auto_c_show)
+	local call_tip_show = test.stub()
+	local _<close> = test.mock(view, 'call_tip_show', call_tip_show)
+
+	test.type('name.func(')
+
+	test.assert_equal(auto_c_show.called, true)
+	local completions = auto_c_show.args[3]
+	test.assert_contains(completions, 'field')
+	test.assert_contains(completions, 'func')
+	test.assert_equal(call_tip_show.called, true)
+end)
+
 test('lsp menu should allow manually starting and stopping an lsp server', function()
 	local _<close> = test.mock(lsp, 'server_commands', {cpp = 'clangd'})
 	local dir<close> = test.tmpdir(clangd_project)

server.lua

@@ -269,6 +269,24 @@ register('textDocument/didChange', function(params)
 	pl_dir.rmtree(tmpdir)
 end)
 
+--- Replaces the conventional 'M' in symbol *symbol* with the file's @module declaration,
+-- if possible.
+-- @param symbol Symbol name that starts with 'M'.
+-- @param params LSP params for the completion/signatureHelp/etc. request.
+-- @return substituted or original symbol
+local function substitute_M(symbol, params)
+	local lines = files[params.textDocument.uri]
+	if not lines then return symbol end
+	for _, line in ipairs(lines) do
+		local module = line:match('^%s*%-%-%-?%s*@module%s([%w_.]+)')
+		if module then
+			log:debug('found module %s; using it instead of M', module)
+			return symbol:gsub('^M', module)
+		end
+	end
+	return symbol
+end
+
 --- Map of expression patterns to their types.
 -- Used for type-hinting when showing autocompletions for variables. Expressions are expected
 -- to match after the '=' sign of a statement.
@@ -293,6 +311,8 @@ register('textDocument/completion', function(params)
 		symbol, op, part)
 	if symbol == '' and part == '' then return json.null end -- nothing to complete
 	symbol, part = symbol:gsub('^_G%.?', ''), part ~= '_G' and part or ''
+	-- Replace conventional M with its @module declaration if possible.
+	if symbol == 'M' then symbol = substitute_M(symbol, params) end
 	-- Attempt to identify string type and file type symbols.
 	local assignment = '%f[%w_]' .. symbol:gsub('(%p)', '%%%1') .. '%s*=%s*(.*)$'
 	for i = line_num - 1, 1, -1 do
@@ -347,6 +367,7 @@ local function get_symbol(params)
 	local symbol_part_right = line:match('^[%w_]*', col_num)
 	local symbol_part_left = line:sub(1, col_num - 1):match('[%w_.:]*$')
 	local symbol = symbol_part_left .. symbol_part_right
+	if symbol:find('^M%.') then symbol = substitute_M(symbol, params) end
 	return symbol ~= '' and symbol or nil
 end
 
@@ -431,6 +452,7 @@ register('textDocument/signatureHelp', function(params)
 		goto retry
 	end
 	local func = text:sub(1, s - 1):match('[%w_.:]+$')
+	if func and func:find('^M%.') then func = substitute_M(func, params) end
 	if not func then return json.null end
 
 	-- Get its signature(s).