feat(options): lua closure/function options

Problem:
Cannot assign Lua functions/closures to "func" ('completefunc',
'tagfun', …) or "expr" ('foldexpr', 'indentexpr', …) options.

Solution:
- Store "func"/"expr" options as `Callback` instead of string.
- Delete oceans of copy-pasted code.
- BREAKING: LuaRef returned via RPC/Vimscript is now represented as
  `"<Lua N: file:line>"` (like what `:map` shows) instead of `nil`.
- Note: `man.vim` still uses `v:lua` string, bc it's a vimscript ftplugin.

Helped-by: Lewis Russell <lewis6991@gmail.com>

runtime/lua/vim/_comment.lua

@@ -221,7 +221,7 @@ local function operator(mode)
   -- Used without arguments as part of expression mapping. Otherwise it is
   -- called as 'operatorfunc'.
   if mode == nil then
-    vim.o.operatorfunc = "v:lua.require'vim._comment'.operator"
+    vim.o.operatorfunc = operator
     return 'g@'
   end
 

runtime/lua/vim/_core/defaults.lua

@@ -446,14 +446,12 @@ 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._core.util'.space_above"
+      vim.go.operatorfunc = 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._core.util'.space_below"
+      vim.go.operatorfunc = require('vim._core.util').space_below
       return 'g@l'
     end, { expr = true, desc = 'Add empty line below cursor' })
   end

runtime/lua/vim/_core/util.lua

@@ -3,7 +3,6 @@
 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
@@ -12,12 +11,10 @@ local function add_blank(above)
   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

runtime/lua/vim/_meta/options.gen.lua

@@ -840,7 +840,7 @@ vim.bo.channel = vim.o.channel
 --- Otherwise the expression is evaluated in the context of the script
 --- where the option was set, thus script-local items are available.
 ---
---- @type string
+--- @type string|function
 vim.o.charconvert = ""
 vim.o.ccv = vim.o.charconvert
 vim.go.charconvert = vim.o.charconvert
@@ -1125,7 +1125,7 @@ vim.bo.cpt = vim.bo.complete
 --- function, a `lambda` or a `Funcref`.  See `option-value-function` for
 --- more information.
 ---
---- @type string
+--- @type string|function
 vim.o.completefunc = ""
 vim.o.cfu = vim.o.completefunc
 vim.bo.completefunc = vim.o.completefunc
@@ -1791,7 +1791,7 @@ vim.go.dia = vim.go.diffanchors
 --- Expression which is evaluated to obtain a diff file (either ed-style
 --- or unified-style) from two versions of a file.  See `diff-diffexpr`.
 ---
---- @type string
+--- @type string|function
 vim.o.diffexpr = ""
 vim.o.dex = vim.o.diffexpr
 vim.go.diffexpr = vim.o.diffexpr
@@ -2672,7 +2672,7 @@ vim.go.fcs = vim.go.fillchars
 --- ```
 ---
 ---
---- @type string
+--- @type string|function
 vim.o.findfunc = ""
 vim.o.ffu = vim.o.findfunc
 vim.bo.findfunc = vim.o.findfunc
@@ -2745,7 +2745,7 @@ vim.wo.fen = vim.wo.foldenable
 --- It is not allowed to change text or jump to another window while
 --- evaluating 'foldexpr' `textlock`.
 ---
---- @type string
+--- @type string|function
 vim.o.foldexpr = "0"
 vim.o.fde = vim.o.foldexpr
 vim.wo.foldexpr = vim.o.foldexpr
@@ -2891,7 +2891,7 @@ vim.go.fdo = vim.go.foldopen
 --- When set to an empty string, foldtext is disabled, and the line
 --- is displayed normally with highlighting and no line wrapping.
 ---
---- @type string
+--- @type string|function
 vim.o.foldtext = "foldtext()"
 vim.o.fdt = vim.o.foldtext
 vim.wo.foldtext = vim.o.foldtext
@@ -2943,7 +2943,7 @@ vim.wo.fdt = vim.wo.foldtext
 --- since changing the buffer text is not allowed.
 --- This option cannot be set in a modeline when 'modelineexpr' is off.
 ---
---- @type string
+--- @type string|function
 vim.o.formatexpr = ""
 vim.o.fex = vim.o.formatexpr
 vim.bo.formatexpr = vim.o.formatexpr
@@ -3522,7 +3522,7 @@ vim.go.inc = vim.go.include
 --- It is not allowed to change text or jump to another window while
 --- evaluating 'includeexpr' `textlock`.
 ---
---- @type string
+--- @type string|function
 vim.o.includeexpr = ""
 vim.o.inex = vim.o.includeexpr
 vim.bo.includeexpr = vim.o.includeexpr
@@ -3617,7 +3617,7 @@ vim.go.is = vim.go.incsearch
 --- It is not allowed to change text or jump to another window while
 --- evaluating 'indentexpr' `textlock`.
 ---
---- @type string
+--- @type string|function
 vim.o.indentexpr = ""
 vim.o.inde = vim.o.indentexpr
 vim.bo.indentexpr = vim.o.indentexpr
@@ -4875,7 +4875,7 @@ vim.wo.nuw = vim.wo.numberwidth
 --- This option is usually set by a filetype plugin:
 --- `:filetype-plugin-on`
 ---
---- @type string
+--- @type string|function
 vim.o.omnifunc = ""
 vim.o.ofu = vim.o.omnifunc
 vim.bo.omnifunc = vim.o.omnifunc
@@ -4886,7 +4886,7 @@ vim.bo.ofu = vim.bo.omnifunc
 --- the name of a function, a `lambda` or a `Funcref`.  See
 --- `option-value-function` for more information.
 ---
---- @type string
+--- @type string|function
 vim.o.operatorfunc = ""
 vim.o.opfunc = vim.o.operatorfunc
 vim.go.operatorfunc = vim.o.operatorfunc
@@ -4923,7 +4923,7 @@ vim.go.para = vim.go.paragraphs
 --- Expression which is evaluated to apply a patch to a file and generate
 --- the resulting new version of the file.  See `diff-patchexpr`.
 ---
---- @type string
+--- @type string|function
 vim.o.patchexpr = ""
 vim.o.pex = vim.o.patchexpr
 vim.go.patchexpr = vim.o.patchexpr
@@ -5191,7 +5191,7 @@ vim.go.pyx = vim.go.pyxversion
 --- It is not allowed to change text or jump to another window while
 --- evaluating 'qftf' `textlock`.
 ---
---- @type string
+--- @type string|function
 vim.o.quickfixtextfunc = ""
 vim.o.qftf = vim.o.quickfixtextfunc
 vim.go.quickfixtextfunc = vim.o.quickfixtextfunc
@@ -7324,7 +7324,7 @@ vim.go.tc = vim.go.tagcase
 --- `lambda` or a `Funcref`.  See `option-value-function` for more
 --- information.
 ---
---- @type string
+--- @type string|function
 vim.o.tagfunc = ""
 vim.o.tfu = vim.o.tagfunc
 vim.bo.tagfunc = vim.o.tagfunc
@@ -7492,7 +7492,7 @@ vim.go.tsr = vim.go.thesaurus
 --- The value can be the name of a function, a `lambda` or a `Funcref`.
 --- See `option-value-function` for more information.
 ---
---- @type string
+--- @type string|function
 vim.o.thesaurusfunc = ""
 vim.o.tsrfu = vim.o.thesaurusfunc
 vim.bo.thesaurusfunc = vim.o.thesaurusfunc

runtime/lua/vim/lsp.lua

@@ -846,12 +846,12 @@ function lsp._set_defaults(client, bufnr)
   if
     client:supports_method('textDocument/definition') and is_empty_or_default(bufnr, 'tagfunc')
   then
-    vim.bo[bufnr].tagfunc = 'v:lua.vim.lsp.tagfunc'
+    vim.bo[bufnr].tagfunc = lsp.tagfunc
   end
   if
     client:supports_method('textDocument/completion') and is_empty_or_default(bufnr, 'omnifunc')
   then
-    vim.bo[bufnr].omnifunc = 'v:lua.vim.lsp.omnifunc'
+    vim.bo[bufnr].omnifunc = lsp.omnifunc
   end
   if
     client:supports_method('textDocument/rangeFormatting')

runtime/lua/vim/lsp/client.lua

@@ -1448,10 +1448,10 @@ end
 --- Reset defaults set by `set_defaults`.
 --- Must only be called if the last client attached to a buffer exits.
 local function reset_defaults(bufnr)
-  if vim.bo[bufnr].tagfunc == 'v:lua.vim.lsp.tagfunc' then
+  if vim.bo[bufnr].tagfunc == vim.lsp.tagfunc then
     vim.bo[bufnr].tagfunc = nil
   end
-  if vim.bo[bufnr].omnifunc == 'v:lua.vim.lsp.omnifunc' then
+  if vim.bo[bufnr].omnifunc == vim.lsp.omnifunc then
     vim.bo[bufnr].omnifunc = nil
   end
   if vim.bo[bufnr].formatexpr == 'v:lua.vim.lsp.formatexpr()' then

runtime/lua/vim/treesitter/dev.lua

@@ -639,7 +639,7 @@ function M.edit_query(lang)
   local query_buf = api.nvim_win_get_buf(query_win)
 
   vim.b[buf].dev_edit = query_win
-  vim.bo[query_buf].omnifunc = 'v:lua.vim.treesitter.query.omnifunc'
+  vim.bo[query_buf].omnifunc = vim.treesitter.query.omnifunc
   set_dev_options(query_win, query_buf)
 
   -- Note that omnifunc guesses the language based on the containing folder,

runtime/lua/vim/treesitter/query.lua

@@ -1131,7 +1131,7 @@ end
 --- Use via
 ---
 --- ```lua
---- vim.bo.omnifunc = 'v:lua.vim.treesitter.query.omnifunc'
+--- vim.bo.omnifunc = vim.treesitter.query.omnifunc
 --- ```
 ---
 --- @param findstart 0|1