fix(options): make 'cdhome' take effect on any platform

Platform specific options are cringe and should either be fixed or
deleted.

In this case, the platform difference can trivially be implemented
using a conditional default value. If the user overrides the value,
then it is because the user wants that value, regardless of the
corporation who manufactured the OS that the user is running.

Possible alternative: delete the option by making it always on.

runtime/doc/options.txt

@@ -1244,12 +1244,11 @@ A jump table for the options with a short description can be found at |Q_op|.
 			This probably only matters for Turkish.
 
 				*'cdhome'* *'cdh'* *'nocdhome'* *'nocdh'*
-'cdhome' 'cdh'		boolean	(default off)
+'cdhome' 'cdh'		boolean	(default on on Unix, off on Windows)
 			global
 	When on, |:cd|, |:tcd| and |:lcd| without an argument changes the
 	current working directory to the |$HOME| directory like in Unix.
 	When off, those commands just print the current directory name.
-	On Unix this option has no effect.
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.
 

runtime/lua/vim/_meta/options.lua

@@ -700,12 +700,11 @@ vim.go.cmp = vim.go.casemap
 --- When on, `:cd`, `:tcd` and `:lcd` without an argument changes the
 --- current working directory to the `$HOME` directory like in Unix.
 --- When off, those commands just print the current directory name.
---- On Unix this option has no effect.
 --- This option cannot be set from a `modeline` or in the `sandbox`, for
 --- security reasons.
 ---
 --- @type boolean
-vim.o.cdhome = false
+vim.o.cdhome = true
 vim.o.cdh = vim.o.cdhome
 vim.go.cdhome = vim.o.cdhome
 vim.go.cdh = vim.go.cdhome

src/nvim/ex_docmd.c

@@ -6105,11 +6105,7 @@ bool changedir_func(char *new_dir, CdScope scope)
 
   // For UNIX ":cd" means: go to home directory.
   // On other systems too if 'cdhome' is set.
-#if defined(UNIX)
-  if (*new_dir == NUL) {
-#else
   if (*new_dir == NUL && p_cdh) {
-#endif
     // Use NameBuff for home directory name.
     expand_env("$HOME", NameBuff, MAXPATHL);
     new_dir = NameBuff;
@@ -6148,13 +6144,11 @@ bool changedir_func(char *new_dir, CdScope scope)
 void ex_cd(exarg_T *eap)
 {
   char *new_dir = eap->arg;
-#if !defined(UNIX)
   // for non-UNIX ":cd" means: print current directory unless 'cdhome' is set
   if (*new_dir == NUL && !p_cdh) {
     ex_pwd(NULL);
     return;
   }
-#endif
 
   CdScope scope = kCdScopeGlobal;
   switch (eap->cmdidx) {

src/nvim/options.lua

@@ -1005,12 +1005,16 @@ local options = {
     },
     {
       abbreviation = 'cdh',
-      defaults = false,
+      defaults = {
+        condition = 'MSWIN',
+        if_false = true,
+        if_true = false,
+        doc = [[on on Unix, off on Windows]],
+      },
       desc = [=[
         When on, |:cd|, |:tcd| and |:lcd| without an argument changes the
         current working directory to the |$HOME| directory like in Unix.
         When off, those commands just print the current directory name.
-        On Unix this option has no effect.
         This option cannot be set from a |modeline| or in the |sandbox|, for
         security reasons.
       ]=],