docs(builtin): overload functions with union return types

runtime/lua/vim/_meta/vimfn.lua

@@ -1843,7 +1843,13 @@ function vim.fn.exp(expr) end
 ---
 --- @param string string
 --- @param nosuf? boolean
---- @param list? any
+--- @param list? nil|false
+--- @return string
+function vim.fn.expand(string, nosuf, list) end
+
+--- @param string string
+--- @param nosuf boolean
+--- @param list true|number|string|table
 --- @return string|string[]
 function vim.fn.expand(string, nosuf, list) end
 
@@ -3138,7 +3144,12 @@ function vim.fn.getjumplist(winnr, tabnr) end
 --- |getbufoneline()|
 ---
 --- @param lnum integer
---- @param end_? any
+--- @param end_? nil|false
+--- @return string
+function vim.fn.getline(lnum, end_) end
+
+--- @param lnum integer
+--- @param end_ true|number|string|table
 --- @return string|string[]
 function vim.fn.getline(lnum, end_) end
 
@@ -3436,7 +3447,12 @@ function vim.fn.getqflist(what) end
 --- If {regname} is not specified, |v:register| is used.
 ---
 --- @param regname? string
---- @param list? any
+--- @param list? nil|false
+--- @return string
+function vim.fn.getreg(regname, list) end
+
+--- @param regname string
+--- @param list true|number|string|table
 --- @return string|string[]
 function vim.fn.getreg(regname, list) end
 
@@ -5067,7 +5083,14 @@ function vim.fn.map(expr1, expr2) end
 --- @param name string
 --- @param mode? string
 --- @param abbr? boolean
---- @param dict? boolean
+--- @param dict? false
+--- @return string
+function vim.fn.maparg(name, mode, abbr, dict) end
+
+--- @param name string
+--- @param mode string
+--- @param abbr boolean
+--- @param dict true
 --- @return string|table<string,any>
 function vim.fn.maparg(name, mode, abbr, dict) end
 
@@ -9317,7 +9340,12 @@ function vim.fn.strwidth(string) end
 --- A line break is included as a newline character.
 ---
 --- @param nr integer
---- @param list? integer
+--- @param list? nil
+--- @return string
+function vim.fn.submatch(nr, list) end
+
+--- @param nr integer
+--- @param list integer
 --- @return string|string[]
 function vim.fn.submatch(nr, list) end