feat(config): Automatically wrap add key in a table.

Inspired by the question in #341. Makes the UX more uniform between the
"simple" version of the `add` key and more advanced callback functions.

lua/nvim-surround/annotations.lua

@@ -6,7 +6,7 @@
 ---@alias position integer[] A 1-indexed position in the buffer
 ---@alias delimiter string[] The text representation of a delimiter
 ---@alias delimiter_pair delimiter[] A pair of delimiters
----@alias add_func fun(char: string|nil): delimiter_pair|nil
+---@alias add_func fun(char: string|nil): delimiter_pair|string[]|nil
 ---@alias find_func fun(char: string|nil): selection|nil
 ---@alias delete_func fun(char: string|nil): selections|nil
 ---@alias change_table { target: delete_func, replacement: add_func|nil }

lua/nvim-surround/config.lua

@@ -360,11 +360,18 @@ M.get_delimiters = function(char, line_mode)
     char = M.get_alias(char)
     -- Get the delimiters, using invalid_key_behavior if the add function is undefined for the character
     local delimiters = M.get_add(char)(char)
-    -- Add new lines if the addition is done line-wise
-    if delimiters and line_mode then
-        local lhs = delimiters[1]
-        local rhs = delimiters[2]
+    if delimiters == nil then
+        return nil
+    end
+    local lhs = type(delimiters[1]) == "string" and { delimiters[1] } or delimiters[1]
+    local rhs = type(delimiters[2]) == "string" and { delimiters[2] } or delimiters[2]
+    -- These casts are needed because LuaLS doesn't narrow types in ternaries properly
+    -- https://github.com/LuaLS/lua-language-server/issues/2233
+    ---@cast lhs string[]
+    ---@cast rhs string[]
 
+    -- Add new lines if the addition is done line-wise
+    if line_mode then
         -- Trim whitespace after the leading delimiter and before the trailing delimiter
         lhs[#lhs] = lhs[#lhs]:gsub("%s+$", "")
         rhs[1] = rhs[1]:gsub("^%s+", "")
@@ -373,7 +380,7 @@ M.get_delimiters = function(char, line_mode)
         table.insert(lhs, "")
     end
 
-    return delimiters
+    return { lhs, rhs }
 end
 
 -- Returns the add key for the surround associated with a given character, if one exists.
@@ -437,12 +444,9 @@ M.translate_add = function(user_add)
     if type(user_add) ~= "table" then
         return user_add
     end
-    -- If the input is given as a pair of strings, or pair of string lists, wrap it in a function
+
     return function()
-        return {
-            functional.to_list(user_add[1]),
-            functional.to_list(user_add[2]),
-        }
+        return user_add
     end
 end
 

tests/configuration_spec.lua

@@ -120,6 +120,26 @@ describe("configuration", function()
         check_lines({ "hey! hello world" })
     end)
 
+    it("can use 'syntactic sugar' for add functions", function()
+        require("nvim-surround").buffer_setup({
+            surrounds = {
+                ["("] = {
+                    add = function()
+                        return { "<<", ">>" }
+                    end,
+                },
+            },
+        })
+
+        set_lines({
+            "hello world",
+        })
+        vim.cmd("normal yss(")
+        check_lines({
+            "<<hello world>>",
+        })
+    end)
+
     it("can disable surrounds", function()
         require("nvim-surround").buffer_setup({
             surrounds = {