build: ship "_core/*" as bytecode (built-into Nvim binary)

Problem:
We want to encourage implementing core features in Lua instead of C, but
it's clumsy because:
- Core Lua code (built into `nvim` so it is available even if VIMRUNTIME
  is missing/invalid) requires manually updating CMakeLists.txt, or
  stuffing it into `_editor.lua`.
- Core Lua modules are not organized similar to C modules, `_editor.lua`
  is getting too big.

Solution:
- Introduce `_core/` where core Lua code can live. All Lua modules added
  there will automatically be included as bytecode in the `nvim` binary.
- Move these core modules into `_core/*`:
  ```
  _defaults.lua
  _editor.lua
  _options.lua
  _system.lua
  shared.lua
  ```

TODO:
- Move `_extui/ => _core/ui2/`

.github/scripts/labeler_configuration.yml

@@ -24,7 +24,7 @@ comment:
 
 defaults:
   - changed-files:
-    - any-glob-to-any-file: [ runtime/lua/vim/_defaults.lua ]
+    - any-glob-to-any-file: [ runtime/lua/vim/_core/defaults.lua ]
 
 diagnostic:
   - changed-files:

CONTRIBUTING.md

@@ -232,10 +232,10 @@ See [#549][549] for more details.
 
 ### Lua runtime files
 
-Most of the Lua core [`runtime/`](./runtime) modules are precompiled to
-bytecode, so changes to those files won't get used unless you rebuild Nvim or
-by passing `--luamod-dev` and `$VIMRUNTIME`. For example, try adding a function
-to `runtime/lua/vim/_editor.lua` then:
+The Lua [`runtime/lua/vim/_core/`](./runtime/lua/vim/_core/) modules are
+precompiled to bytecode, so changes won't be usable unless you (1) rebuild Nvim
+or (2) start Nvim with `--luamod-dev` and `$VIMRUNTIME`. For example try adding
+a function to `runtime/lua/vim/editor.lua`, then:
 
 ```bash
 VIMRUNTIME=./runtime ./build/bin/nvim --luamod-dev

cmake/RunTests.cmake

@@ -69,7 +69,7 @@ endif()
 
 execute_process(
   # Note: because of "-ll" (low-level interpreter mode), some modules like
-  # _editor.lua are not loaded.
+  # _core/editor.lua are not loaded.
   COMMAND ${NVIM_PRG} -ll ${WORKING_DIR}/test/lua_runner.lua ${DEPS_INSTALL_DIR}/share/lua/5.1/ busted -v -o test.busted.outputHandlers.nvim
     --lazy --helper=${TEST_DIR}/${TEST_TYPE}/preload.lua
     --lpath=${BUILD_DIR}/?.lua

runtime/doc/dev.txt

@@ -277,7 +277,7 @@ Docstring format:
 - Files declared as `@meta` are only used for typing and documentation (similar to "*.d.ts" typescript files).
 
 Example: the help for |vim.paste()| is generated from a docstring decorating
-vim.paste in runtime/lua/vim/_editor.lua like this: >
+vim.paste in runtime/lua/vim/_core/editor.lua like this: >
 
     --- Paste handler, invoked by |nvim_paste()| when a conforming UI
     --- (such as the |TUI|) pastes text into the editor.

runtime/doc/dev_arch.txt

@@ -20,17 +20,64 @@ The purpose of this document is to give:
                                   Type |gO| to see the table of contents.
 
 ==============================================================================
-Filename conventions
+Project layout: where things go
 
-The source filenames use extensions to hint about their purpose.
+C CODE
 
+- Nvim C code lives in `src/nvim/`.
+    - This includes third-party components which we have forked and fully
+      "own", meaning we no longer track the upstream. In particular: `vterm/`
+      and `tui/termkey/`.
+- Vendored third-party components live in `src/*`.
+    - `src/tee/` and `src/xxd/` have their own build files. They are shipped
+      with the Windows artifact to ensure those tools exists there.
+    - Other components like `src/cjson/` and `src/mpack/` are included with
+      Nvim itself. These vendored sources are synced from upstream, we do not
+      "own" them.
+
+See also "MAINTAIN.md".
+
+Generated C files use these filename conventions to hint their purpose:
 - `*.c`, `*.generated.c` - full C files, with all includes, etc.
 - `*.c.h` - parametrized C files, contain all necessary includes, but require
   defining macros before actually using. Example: `typval_encode.c.h`
-- `*.h` - full headers, with all includes. Does *not* apply to `*.generated.h`.
+- `*.h` - full headers, with all includes. Does not apply to `*.generated.h`.
 - `*.h.generated.h` - exported functions’ declarations.
 - `*.c.generated.h` - static functions’ declarations.
 
+
+LUA CODE
+
+Lua code lives in one of four places:
+
+1. Plugins! Not everything needs to live on `vim.*`. Plugins are the correct
+   model for non-essential features which the user may disable or replace with
+   a third-party plugin, and which do not have a formal API. Examples:
+   "editorconfig", "comment".
+   - "opt-out": `runtime/plugin/`
+   - "opt-in": `runtime/pack/dist/opt/`
+2. `runtime/lua/vim/` (the runtime): Lazy-loaded modules. Examples: `treesitter`, `lpeg`.
+3. `runtime/lua/vim/_core/shared.lua`: pure Lua functions which always are available.
+   Used in the test runner, and worker threads/processes launched from Nvim.
+4. `runtime/lua/vim/_core/`: Eager-loaded code which directly interacts with the Nvim
+   editor state. Only available in the main thread. See |dev-lua-builtin|
+   below.
+
+The top-level `vim.` namespace is for fundamental Lua and editor features. Use
+submodules (`vim.foo`) for everything else (but avoid excessive "nesting"), or
+plugins (see above).
+
+Compatibility with Vim's `if_lua` is explicitly a non-goal.
+
+                                                             *dev-lua-builtin*
+Lua modules that are necessary even if VIMRUNTIME is invalid (generally, data
+structures and essential utilties), must be compiled into the `nvim` binary.
+There are two ways to do that:
+- if they are private, put the code file in `runtime/lua/vim/_core/`
+- if they are public, choose a new filepath in `runtime/lua/vim/`
+  and add it to VIM_MODULE_FILE in src/nvim/CMakeLists.txt.
+
+
 ==============================================================================
 Data structures
 

runtime/doc/dev_test.txt

@@ -270,8 +270,8 @@ Limitations:
       require("lldebugger").start()
     end
 <  This is a [local-lua-debugger limitation](https://github.com/tomblind/local-lua-debugger-vscode?tab=readme-ov-file#busted)
-- You cannot step into code of files which get baked into the nvim binary like
-  the `shared.lua`.
+- You cannot step into code of files which get baked into the nvim binary
+  (such as `_core/*.lua` and `inspect.lua`).
 
 
 ------------------------------------------------------------------------------

runtime/embedded_data.zig

@@ -1,3 +1,3 @@
 pub const inspect_module = @embedFile("./lua/vim/inspect.lua");
-pub const shared_module = @embedFile("./lua/vim/shared.lua");
+pub const shared_module = @embedFile("./lua/vim/_core/shared.lua");
 pub const iter_module = @embedFile("./lua/vim/iter.lua");

runtime/lua/vim/_buf.lua

@@ -1,23 +0,0 @@
-local M = {}
-
---- Adds one or more blank lines above or below the cursor.
--- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
---- @param above? boolean Place blank line(s) above the cursor
-local function add_blank(above)
-  local offset = above and 1 or 0
-  local repeated = vim.fn['repeat']({ '' }, vim.v.count1)
-  local linenr = vim.api.nvim_win_get_cursor(0)[1]
-  vim.api.nvim_buf_set_lines(0, linenr - offset, linenr - offset, true, repeated)
-end
-
--- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
-function M.space_above()
-  add_blank(true)
-end
-
--- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
-function M.space_below()
-  add_blank()
-end
-
-return M

runtime/lua/vim/_core/defaults.lua

@@ -1,3 +1,5 @@
+-- Default user-commands, autocmds, mappings, menus.
+
 --- Default user commands
 do
   vim.api.nvim_create_user_command('Inspect', function(cmd)
@@ -440,13 +442,13 @@ do
     -- Add empty lines
     vim.keymap.set('n', '[<Space>', function()
       -- TODO: update once it is possible to assign a Lua function to options #25672
-      vim.go.operatorfunc = "v:lua.require'vim._buf'.space_above"
+      vim.go.operatorfunc = "v:lua.require'vim._core.util'.space_above"
       return 'g@l'
     end, { expr = true, desc = 'Add empty line above cursor' })
 
     vim.keymap.set('n', ']<Space>', function()
       -- TODO: update once it is possible to assign a Lua function to options #25672
-      vim.go.operatorfunc = "v:lua.require'vim._buf'.space_below"
+      vim.go.operatorfunc = "v:lua.require'vim._core.util'.space_below"
       return 'g@l'
     end, { expr = true, desc = 'Add empty line below cursor' })
   end

runtime/lua/vim/_core/editor.lua

@@ -1,27 +1,5 @@
 -- Nvim-Lua stdlib: the `vim` module (:help lua-stdlib)
 --
--- Lua code lives in one of four places:
---    1. Plugins! Not everything needs to live on "vim.*". Plugins are the correct model for
---       non-essential features which the user may want to disable or replace with a third-party
---       plugin. Examples: "editorconfig", "comment".
---       - "opt-out": runtime/plugin/*.lua
---       - "opt-in": runtime/pack/dist/opt/
---    2. runtime/lua/vim/ (the runtime): Lazy-loaded modules. Examples: `inspect`, `lpeg`.
---    3. runtime/lua/vim/shared.lua: pure Lua functions which always are available. Used in the test
---       runner, and worker threads/processes launched from Nvim.
---    4. runtime/lua/vim/_editor.lua: Eager-loaded code which directly interacts with the Nvim
---       editor state. Only available in the main thread.
---
--- The top level "vim.*" namespace is for fundamental Lua and editor features. Use submodules for
--- everything else (but avoid excessive "nesting"), or plugins (see above).
---
--- Compatibility with Vim's `if_lua` is explicitly a non-goal.
---
--- Reference (#6580):
---    - https://github.com/luafun/luafun
---    - https://github.com/rxi/lume
---    - http://leafo.net/lapis/reference/utilities.html
---    - https://github.com/bakpakin/Fennel (pretty print, repl)
 
 -- These are for loading runtime modules lazily since they aren't available in
 -- the nvim binary as specified in executor.c
@@ -1321,7 +1299,7 @@ function vim.deprecate(name, alternative, version, plugin, backtrace)
   end
 end
 
-require('vim._options')
+require('vim._core.options')
 
 --- Remove at Nvim 1.0
 ---@deprecated

runtime/lua/vim/_core/exrc.lua

@@ -1,3 +1,5 @@
+-- For 'exrc' and related functionality.
+
 local files = vim.fs.find({ '.nvim.lua', '.nvimrc', '.exrc' }, {
   type = 'file',
   upward = true,

runtime/lua/vim/_core/server.lua

@@ -1,3 +1,5 @@
+-- For "--listen" and related functionality.
+
 local M = {}
 
 --- Called by builtin serverlist(). Returns all running servers in stdpath("run").

runtime/lua/vim/_core/stringbuffer.lua

@@ -13,7 +13,7 @@ if has_strbuffer then
   -- Lua 5.1 does not have __len metamethod so we need to provide a len()
   -- function to use instead.
 
-  --- @param buf vim._stringbuffer
+  --- @param buf vim._core.stringbuffer
   --- @return integer
   function M.len(buf)
     return #buf
@@ -22,7 +22,7 @@ if has_strbuffer then
   return M
 end
 
---- @class vim._stringbuffer
+--- @class vim._core.stringbuffer
 --- @field private buf string[]
 --- @field package len integer absolute length of the `buf`
 --- @field package skip_ptr integer
@@ -103,7 +103,7 @@ function M.new()
   return setmetatable({}, StrBuffer):reset()
 end
 
---- @param buf vim._stringbuffer
+--- @param buf vim._core.stringbuffer
 function M.len(buf)
   return buf.len - buf.skip_ptr
 end

runtime/lua/vim/_core/util.lua

@@ -1,5 +1,27 @@
+-- Nursery for random things that may later find their way into stdlib if they mature.
+
 local M = {}
 
+--- Adds one or more blank lines above or below the cursor.
+-- TODO: move to _core/defaults.lua once it is possible to assign a Lua function to options #25672
+--- @param above? boolean Place blank line(s) above the cursor
+local function add_blank(above)
+  local offset = above and 1 or 0
+  local repeated = vim.fn['repeat']({ '' }, vim.v.count1)
+  local linenr = vim.api.nvim_win_get_cursor(0)[1]
+  vim.api.nvim_buf_set_lines(0, linenr - offset, linenr - offset, true, repeated)
+end
+
+-- TODO: move to _core/defaults.lua once it is possible to assign a Lua function to options #25672
+function M.space_above()
+  add_blank(true)
+end
+
+-- TODO: move to _core/defaults.lua once it is possible to assign a Lua function to options #25672
+function M.space_below()
+  add_blank()
+end
+
 --- Edit a file in a specific window
 --- @param winnr number
 --- @param file string

runtime/lua/vim/_init_packages.lua

@@ -95,6 +95,6 @@ end
 
 -- only on main thread: functions for interacting with editor state
 if vim.api and not vim.is_thread() then
-  require('vim._editor')
-  require('vim._system')
+  require('vim._core.editor')
+  require('vim._core.system')
 end

runtime/lua/vim/lsp/rpc.lua

@@ -1,7 +1,7 @@
 local log = require('vim.lsp.log')
 local protocol = require('vim.lsp.protocol')
 local lsp_transport = require('vim.lsp._transport')
-local strbuffer = require('vim._stringbuffer')
+local strbuffer = require('vim._core.stringbuffer')
 local validate, schedule_wrap = vim.validate, vim.schedule_wrap
 
 --- Embeds the given string into a table and correctly computes `Content-Length`.

src/gen/gen_steps.zig

@@ -72,21 +72,47 @@ pub fn nvim_gen_sources(
         const names = [_][]const u8{
             "_init_packages",
             "inspect",
-            "_editor",
-            "_system",
             "filetype",
             "fs",
             "F",
             "keymap",
             "loader",
-            "_defaults",
-            "_options",
-            "shared",
+            "text",
         };
         for (names) |n| {
             gen_step.addFileArg(b.path(b.fmt("runtime/lua/vim/{s}.lua", .{n})));
             gen_step.addArg(b.fmt("vim.{s}", .{n}));
         }
+
+        // Dynamically add all Lua _core/ modules (like CMakeLists.txt does)
+        if (b.build_root.handle.openDir("runtime/lua/vim/_core", .{ .iterate = true })) |core_dir_handle| {
+            var core_dir = core_dir_handle;
+            defer core_dir.close();
+
+            var iter = core_dir.iterate();
+            var core_files = try std.ArrayList([]const u8).initCapacity(b.allocator, 0);
+            defer core_files.deinit(b.allocator);
+
+            while (try iter.next()) |entry| {
+                if (entry.kind == .file and std.mem.endsWith(u8, entry.name, ".lua")) {
+                    const module_name = try b.allocator.dupe(u8, entry.name[0 .. entry.name.len - 4]);
+                    try core_files.append(b.allocator, module_name);
+                }
+            }
+
+            std.mem.sort([]const u8, core_files.items, {}, struct {
+                fn lessThan(_: void, a: []const u8, c: []const u8) bool {
+                    return std.mem.lessThan(u8, a, c);
+                }
+            }.lessThan);
+
+            for (core_files.items) |n| {
+                gen_step.addFileArg(b.path(b.fmt("runtime/lua/vim/_core/{s}.lua", .{n})));
+                gen_step.addArg(b.fmt("vim._core.{s}", .{n}));
+            }
+        } else |err| {
+            std.debug.print("Warning: Could not open _core directory: {}\n", .{err});
+        }
     }
 
     const ui_metadata = ui_step: {

src/gen/gen_vimdoc.lua

@@ -152,8 +152,8 @@ local config = {
     section_order = {
       -- Sections at the top, in a specific order:
       'builtin.lua',
-      '_options.lua',
-      '_editor.lua',
+      'options.lua',
+      'editor.lua',
       '_inspector.lua',
       'shared.lua',
 
@@ -177,7 +177,7 @@ local config = {
       'secure.lua',
       'snippet.lua',
       'spell.lua',
-      '_system.lua',
+      'system.lua',
       'text.lua',
       'ui.lua',
       'uri.lua',
@@ -187,7 +187,9 @@ local config = {
       '_extui.lua',
     },
     files = {
-      'runtime/lua/vim/_editor.lua',
+      'runtime/lua/vim/_core/editor.lua',
+      'runtime/lua/vim/_core/options.lua',
+      'runtime/lua/vim/_core/system.lua',
       'runtime/lua/vim/_extui.lua',
       'runtime/lua/vim/_inspector.lua',
       'runtime/lua/vim/_meta/base64.lua',
@@ -198,8 +200,6 @@ local config = {
       'runtime/lua/vim/_meta/re.lua',
       'runtime/lua/vim/_meta/regex.lua',
       'runtime/lua/vim/_meta/spell.lua',
-      'runtime/lua/vim/_options.lua',
-      'runtime/lua/vim/_system.lua',
       'runtime/lua/vim/filetype.lua',
       'runtime/lua/vim/fs.lua',
       'runtime/lua/vim/glob.lua',
@@ -219,7 +219,7 @@ local config = {
       'runtime/lua/vim/version.lua',
     },
     fn_xform = function(fun)
-      if contains(fun.module, { 'vim.uri', 'vim.shared', 'vim._editor' }) then
+      if contains(fun.module, { 'vim.uri', 'vim.shared', 'vim._core.editor' }) then
         fun.module = 'vim'
       end
 
@@ -238,11 +238,11 @@ local config = {
     },
     section_fmt = function(name)
       name = name:lower()
-      if name == '_editor' then
+      if name == 'editor' then
         return 'Lua module: vim'
-      elseif name == '_system' then
+      elseif name == 'system' then
         return 'Lua module: vim.system'
-      elseif name == '_options' then
+      elseif name == 'options' then
         return 'LUA-VIMSCRIPT BRIDGE'
       elseif name == 'builtin' then
         return 'VIM'
@@ -250,11 +250,11 @@ local config = {
       return 'Lua module: vim.' .. name
     end,
     helptag_fmt = function(name)
-      if name == '_editor' then
+      if name == 'Editor' then
         return 'lua-vim'
-      elseif name == '_system' then
+      elseif name == 'System' then
         return 'lua-vim-system'
-      elseif name == '_options' then
+      elseif name == 'Options' then
         return 'lua-vimscript'
       end
       return 'vim.' .. name:lower()

src/nvim/CMakeLists.txt

@@ -340,20 +340,26 @@ set(LUA_API_C_BINDINGS ${GENERATED_DIR}/lua_api_c_bindings.generated.h)
 set(VIM_MODULE_FILE ${GENERATED_DIR}/lua/vim_module.generated.h)
 
 # NVIM_RUNTIME_DIR
-set(LUA_DEFAULTS_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/_defaults.lua)
-set(LUA_EDITOR_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/_editor.lua)
-set(LUA_SYSTEM_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/_system.lua)
 set(LUA_FILETYPE_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/filetype.lua)
 set(LUA_FS_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/fs.lua)
 set(LUA_F_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/F.lua)
+# Must be item 1 in `builtin_modules`, for `--luamod-dev`.
 set(LUA_INIT_PACKAGES_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/_init_packages.lua)
+# Must be item 2 in `builtin_modules`, for `--luamod-dev`.
 set(LUA_INSPECT_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/inspect.lua)
 set(LUA_KEYMAP_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/keymap.lua)
 set(LUA_LOADER_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/loader.lua)
-set(LUA_OPTIONS_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/_options.lua)
 set(LUA_SHARED_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/shared.lua)
 set(LUA_TEXT_MODULE_SOURCE ${NVIM_RUNTIME_DIR}/lua/vim/text.lua)
 
+# Find all Lua modules in the _core/ directory.
+file(GLOB LUA_CORE_MODULE_SOURCES ${NVIM_RUNTIME_DIR}/lua/vim/_core/*.lua)
+set(LUA_CORE_COMMAND_ARGS)
+foreach(core_source ${LUA_CORE_MODULE_SOURCES})
+  get_filename_component(core_filename ${core_source} NAME_WE)
+  list(APPEND LUA_CORE_COMMAND_ARGS ${core_source} "vim._core.${core_filename}")
+endforeach()
+
 file(GLOB API_HEADERS CONFIGURE_DEPENDS api/*.h)
 list(REMOVE_ITEM API_HEADERS ${CMAKE_CURRENT_LIST_DIR}/api/ui_events.in.h)
 file(GLOB MSGPACK_RPC_HEADERS CONFIGURE_DEPENDS msgpack_rpc/*.h)
@@ -630,32 +636,26 @@ add_custom_command(
       # respectively, otherwise --luamod-dev won't work properly.
       ${LUA_INIT_PACKAGES_MODULE_SOURCE} "vim._init_packages"
       ${LUA_INSPECT_MODULE_SOURCE} "vim.inspect"
-      ${LUA_EDITOR_MODULE_SOURCE} "vim._editor"
-      ${LUA_SYSTEM_MODULE_SOURCE} "vim._system"
       ${LUA_FILETYPE_MODULE_SOURCE} "vim.filetype"
       ${LUA_FS_MODULE_SOURCE} "vim.fs"
       ${LUA_F_MODULE_SOURCE} "vim.F"
       ${LUA_KEYMAP_MODULE_SOURCE} "vim.keymap"
       ${LUA_LOADER_MODULE_SOURCE} "vim.loader"
-      ${LUA_DEFAULTS_MODULE_SOURCE} "vim._defaults"
-      ${LUA_OPTIONS_MODULE_SOURCE} "vim._options"
       ${LUA_SHARED_MODULE_SOURCE} "vim.shared"
       ${LUA_TEXT_MODULE_SOURCE} "vim.text"
+      ${LUA_CORE_COMMAND_ARGS}
   DEPENDS
     ${CHAR_BLOB_GENERATOR}
     ${LUA_INIT_PACKAGES_MODULE_SOURCE}
     ${LUA_INSPECT_MODULE_SOURCE}
-    ${LUA_EDITOR_MODULE_SOURCE}
-    ${LUA_SYSTEM_MODULE_SOURCE}
     ${LUA_FILETYPE_MODULE_SOURCE}
     ${LUA_FS_MODULE_SOURCE}
     ${LUA_F_MODULE_SOURCE}
     ${LUA_KEYMAP_MODULE_SOURCE}
     ${LUA_LOADER_MODULE_SOURCE}
-    ${LUA_DEFAULTS_MODULE_SOURCE}
-    ${LUA_OPTIONS_MODULE_SOURCE}
     ${LUA_SHARED_MODULE_SOURCE}
     ${LUA_TEXT_MODULE_SOURCE}
+    ${LUA_CORE_MODULE_SOURCES}
   VERBATIM
 )
 

src/nvim/cmdexpand.c

@@ -2875,7 +2875,7 @@ static char *get_lsp_arg(expand_T *xp FUNC_ATTR_UNUSED, int idx)
 
     ADD_C(args, CSTR_AS_OBJ(xp->xp_line));
     // Build the current command line as a Lua string argument
-    Object res = NLUA_EXEC_STATIC("return require'vim._core.ex_cmd.lsp'.lsp_complete(...)", args,
+    Object res = NLUA_EXEC_STATIC("return require'vim._core.ex_cmd'.lsp_complete(...)", args,
                                   kRetObject, NULL,
                                   &err);
     api_clear_error(&err);

src/nvim/ex_docmd.c

@@ -8061,7 +8061,7 @@ static void ex_lsp(exarg_T *eap)
 
   ADD_C(args, CSTR_AS_OBJ(eap->arg));
 
-  NLUA_EXEC_STATIC("require'vim._core.ex_cmd.lsp'.ex_lsp(...)", args, kRetNilBool, NULL, &err);
+  NLUA_EXEC_STATIC("require'vim._core.ex_cmd'.ex_lsp(...)", args, kRetNilBool, NULL, &err);
   if (ERROR_SET(&err)) {
     emsg_multiline(err.msg, "lua_error", HLF_E, true);
   }

src/nvim/lua/executor.c

@@ -2137,8 +2137,8 @@ void nlua_set_sctx(sctx_T *current)
   // Files where internal wrappers are defined so we can ignore them
   // like vim.o/opt etc are defined in _options.lua
   char *ignorelist[] = {
-    "vim/_editor.lua",
-    "vim/_options.lua",
+    "vim/_core/editor.lua",
+    "vim/_core/options.lua",
     "vim/keymap.lua",
   };
   int ignorelist_size = sizeof(ignorelist) / sizeof(ignorelist[0]);
@@ -2404,14 +2404,14 @@ plain: {}
   return arena_printf(arena, "<Lua %d>", ref).data;
 }
 
-/// Execute the vim._defaults module to set up default mappings and autocommands
+/// Execute the vim._core.defaults module to set up default mappings and autocommands
 void nlua_init_defaults(void)
 {
   lua_State *const L = global_lstate;
   assert(L);
 
   lua_getglobal(L, "require");
-  lua_pushstring(L, "vim._defaults");
+  lua_pushstring(L, "vim._core.defaults");
   if (nlua_pcall(L, 1, 0)) {
     fprintf(stderr, "%s\n", lua_tostring(L, -1));
   }

src/nvim/tui/input.c

@@ -740,7 +740,7 @@ static void handle_unknown_csi(TermInput *input, const TermKeyKey *key)
         // The second argument tells us whether the OS theme is set to light
         // mode or dark mode, but all we care about is the background color of
         // the terminal emulator. We query for that with OSC 11 and the response
-        // is handled by the autocommand created in _defaults.lua. The terminal
+        // is handled by the autocommand created in _core/defaults.lua. The terminal
         // may send us multiple notifications all at once so we use a timer to
         // coalesce the queries.
         if (uv_timer_get_due_in(&input->bg_query_timer) > 0) {

src/nvim/tui/tui.c

@@ -337,11 +337,9 @@ static void tui_reset_key_encoding(TUIData *tui)
   }
 }
 
-/// Write the OSC 11 sequence to the terminal emulator to query the current
-/// background color.
+/// Write the OSC 11 sequence to the terminal emulator to query the current background color.
 ///
-/// The response will be handled by the TermResponse autocommand created in
-/// _defaults.lua.
+/// Response will be handled by the TermResponse handler in _core/defaults.lua.
 void tui_query_bg_color(TUIData *tui)
   FUNC_ATTR_NONNULL_ALL
 {
@@ -1984,7 +1982,7 @@ static void terminfo_set_str(TUIData *tui, TerminfoDef str, const char *val)
 /// Determine if the terminal supports truecolor or not.
 ///
 /// note: We get another chance at detecting these in the nvim server process, see
-/// the use of vim.termcap in runtime/lua/vim/_defaults.lua
+/// the use of vim.termcap in runtime/lua/vim/_core/defaults.lua
 ///
 /// If terminfo contains Tc, RGB, or both setrgbf and setrgbb capabilities, return true.
 static bool term_has_truecolor(TUIData *tui, const char *colorterm)

test/functional/core/main_spec.lua

@@ -202,3 +202,50 @@ describe('command-line option', function()
     end
   end
 end)
+
+describe('vim._core', function()
+  it('works with "-u NONE" and no VIMRUNTIME', function()
+    clear {
+      args_rm = { '-u' },
+      args = { '-u', 'NONE' },
+      env = { VIMRUNTIME = 'non-existent' },
+    }
+
+    -- `vim.hl` is NOT a builtin module.
+    t.matches("^module 'vim%.hl' not found:", t.pcall_err(n.exec_lua, [[require('vim.hl')]]))
+
+    -- All `vim._core.*` modules are builtin.
+    t.eq({ 'serverlist' }, n.exec_lua([[return vim.tbl_keys(require('vim._core.server'))]]))
+    local expected = {
+      'vim.F',
+      'vim._core.defaults',
+      'vim._core.editor',
+      'vim._core.ex_cmd',
+      'vim._core.exrc',
+      'vim._core.options',
+      'vim._core.server',
+      'vim._core.stringbuffer',
+      'vim._core.system',
+      'vim._core.util',
+      'vim._init_packages',
+      'vim.filetype',
+      'vim.fs',
+      'vim.inspect',
+      'vim.keymap',
+      'vim.loader',
+      'vim.shared',
+      'vim.text',
+    }
+    if n.exec_lua [[return not not _G.jit]] then
+      expected = vim.list_extend({
+        'ffi',
+        'jit.profile',
+        'jit.util',
+        'string.buffer',
+        'table.clear',
+        'table.new',
+      }, expected)
+    end
+    t.eq(expected, n.exec_lua([[local t = vim.tbl_keys(package.preload); table.sort(t); return t]]))
+  end)
+end)

test/functional/core/startup_spec.lua

@@ -72,7 +72,7 @@ describe('startup', function()
     clear({ args = { '--startuptime', testfile } })
     assert_log('Embedded', testfile, 100)
     assert_log('sourcing', testfile, 100)
-    assert_log("require%('vim%._editor'%)", testfile, 100)
+    assert_log("require%('vim%._core.editor'%)", testfile, 100)
   end)
 
   it('--startuptime does not crash on error #31125', function()
@@ -1208,12 +1208,7 @@ describe('user config init', function()
     mkdir_p(xconfig .. pathsep .. 'nvim')
     mkdir_p(xdata)
 
-    write_file(
-      init_lua_path,
-      [[
-      vim.g.lua_rc = 1
-    ]]
-    )
+    write_file(init_lua_path, [[vim.g.lua_rc = 1]])
   end)
 
   after_each(function()
@@ -1240,10 +1235,10 @@ describe('user config init', function()
           exrc_path,
           string.format(
             [[
-          vim.g.exrc_file = "%s"
-          vim.g.exrc_path = debug.getinfo(1, 'S').source:gsub('^@', '')
-          vim.g.exrc_count = (vim.g.exrc_count or 0) + 1
-        ]],
+              vim.g.exrc_file = "%s"
+              vim.g.exrc_path = debug.getinfo(1, 'S').source:gsub('^@', '')
+              vim.g.exrc_count = (vim.g.exrc_count or 0) + 1
+            ]],
             exrc_path
           )
         )
@@ -1252,10 +1247,10 @@ describe('user config init', function()
           exrc_path,
           string.format(
             [[
-          let g:exrc_file = "%s"
-          " let g:exrc_path = ??
-          let g:exrc_count = get(g:, 'exrc_count', 0) + 1
-        ]],
+              let g:exrc_file = "%s"
+              " let g:exrc_path = ??
+              let g:exrc_count = get(g:, 'exrc_count', 0) + 1
+            ]],
             exrc_path
           )
         )
@@ -1270,9 +1265,9 @@ describe('user config init', function()
       write_file(
         init_lua_path,
         [[
-        vim.o.exrc = true
-        vim.g.exrc_file = '---'
-      ]]
+          vim.o.exrc = true
+          vim.g.exrc_file = '---'
+        ]]
       )
       mkdir_p(xstate .. pathsep .. (is_os('win') and 'nvim-data' or 'nvim'))
     end)
@@ -1395,8 +1390,8 @@ describe('user config init', function()
       write_file(
         custom_lua_path,
         [[
-      vim.g.custom_lua_rc = 1
-      ]]
+          vim.g.custom_lua_rc = 1
+        ]]
       )
     end)
 
@@ -1523,16 +1518,16 @@ describe('runtime:', function()
     write_file(
       table.concat({ plugin_folder_path, 'plugin.vim' }, pathsep),
       [[
-      let &runtimepath = &runtimepath
-      let g:vim_plugin = 1
-    ]]
+        let &runtimepath = &runtimepath
+        let g:vim_plugin = 1
+      ]]
     )
     write_file(
       table.concat({ plugin_folder_path, 'plugin.lua' }, pathsep),
       [[
-      vim.o.runtimepath = vim.o.runtimepath
-      vim.g.lua_plugin = 1
-    ]]
+        vim.o.runtimepath = vim.o.runtimepath
+        vim.g.lua_plugin = 1
+      ]]
     )
 
     clear { args_rm = { '-u' }, args = { '--cmd', 'packloadall' }, env = xenv }
@@ -1610,8 +1605,8 @@ describe('user session', function()
     write_file(
       session_file,
       [[
-      vim.g.lua_session = 1
-    ]]
+        vim.g.lua_session = 1
+      ]]
     )
   end)
 

test/functional/ex_cmds/lsp_spec.lua

@@ -28,8 +28,8 @@ describe(':lsp', function()
       args = { '-u', 'NONE' },
       env = { VIMRUNTIME = 'non-existent' },
     }
-    eq(
-      [[Vim(lsp):Lua: [string "<nvim>"]:0: module 'vim._core.ex_cmd.lsp' not found:]],
+    t.matches(
+      [[Vim%(lsp%):Lua: .*module 'vim%.lsp' not found:]],
       vim.split(t.pcall_err(n.command, 'lsp enable dummy'), '\n')[1]
     )
   end)

test/functional/ui/messages_spec.lua

@@ -2053,6 +2053,7 @@ vimComment     xxx match /\s"[^\-:.%#=*].*$/ms=s+1,lc=1  excludenl contains=@vim
   end)
 
   it('no wait return before delayed exception error message', function()
+    screen:try_resize(70, 7)
     feed('ia<esc>:lua vim.cmd.quit()<CR>')
     screen:expect({
       any = {

test/old/testdir/setup.vim

@@ -73,7 +73,7 @@ aunmenu *
 tlunmenu *
 autocmd! nvim.popupmenu
 
-" Undo the 'grepprg' and 'grepformat' setting in _defaults.lua.
+" Undo the 'grepprg' and 'grepformat' setting in _core/defaults.lua.
 set grepprg& grepformat&
 
 " Prevent Nvim log from writing to stderr.