patch 8.2.3780: ":cd" works differently on MS-Windows

Problem:    ":cd" works differently on MS-Windows.
Solution:   Add the 'cdhome' option. (closes #9324)

runtime/doc/editing.txt

@@ -1298,11 +1298,12 @@ Changing directory fails when the current buffer is modified, the '.' flag is
 present in 'cpoptions' and "!" is not used in the command.
 
 							*:cd* *E747* *E472*
-:cd[!]			On non-Unix systems: Print the current directory
+:cd[!]			On non-Unix systems when 'cdhome' is off: Print the
-			name.  On Unix systems: Change the current directory
+			current directory name.
-			to the home directory.  Use |:pwd| to print the
+			Otherwise: Change the current directory to the home
-			current directory on all systems.
+			directory.  Clear any window-local directory.
-			On Unix systems: clear any window-local directory.
+			Use |:pwd| to print the current directory on all
+			systems.
 
 :cd[!] {path}		Change the current directory to {path}.
 			If {path} is relative, it is searched for in the

runtime/doc/quickref.txt

@@ -635,6 +635,7 @@ Short explanation of each option:		*option-list*
 'buflisted'	  'bl'	    whether the buffer shows up in the buffer list
 'buftype'	  'bt'	    special type of buffer
 'casemap'	  'cmp'     specifies how case of letters is changed
+'cdhome'	  'cdh'	    change directory to the home directory by ":cd"
 'cdpath'	  'cd'	    list of directories searched with ":cd"
 'cedit'			    key used to open the command-line window
 'charconvert'	  'ccv'     expression for character encoding conversion

runtime/optwin.vim

@@ -260,6 +260,10 @@ call <SID>OptionG("sect", &sect)
 call <SID>AddOption("path", gettext("list of directory names used for file searching"))
 call append("$", "\t" .. s:global_or_local)
 call <SID>OptionG("pa", &pa)
+if exists("+cdhome")
+  call <SID>AddOption("cdhome", gettext("change directory to the home directory by :cd"))
+  call <SID>BinOptionG("cdh", &cdh)
+endif
 call <SID>AddOption("cdpath", gettext("list of directory names used for :cd"))
 call <SID>OptionG("cd", &cd)
 if exists("+autochdir")

src/ex_docmd.c

@@ -7402,9 +7402,13 @@ changedir_func(
     else
 	prev_dir = pdir;
 
+    // For UNIX ":cd" means: go to home directory.
+    // On other systems too if 'cdhome' is set.
 #if defined(UNIX) || defined(VMS)
-    // for UNIX ":cd" means: go to home directory
     if (*new_dir == NUL)
+#else
+    if (*new_dir == NUL && p_cdh)
+#endif
     {
 	// use NameBuff for home directory name
 # ifdef VMS
@@ -7420,7 +7424,6 @@ changedir_func(
 # endif
 	new_dir = NameBuff;
     }
-#endif
     dir_differs = new_dir == NULL || pdir == NULL
 	|| pathcmp((char *)pdir, (char *)new_dir, -1) != 0;
     if (new_dir == NULL || (dir_differs && vim_chdir(new_dir)))
@@ -7459,8 +7462,8 @@ ex_cd(exarg_T *eap)
 
     new_dir = eap->arg;
 #if !defined(UNIX) && !defined(VMS)
-    // for non-UNIX ":cd" means: print current directory
+    // for non-UNIX ":cd" means: print current directory unless 'cdhome' is set
-    if (*new_dir == NUL)
+    if (*new_dir == NUL && !p_cdh)
 	ex_pwd(NULL);
     else
 #endif

src/option.h

@@ -1094,6 +1094,7 @@ EXTERN int	p_write;	// 'write'
 EXTERN int	p_wa;		// 'writeany'
 EXTERN int	p_wb;		// 'writebackup'
 EXTERN long	p_wd;		// 'writedelay'
+EXTERN int	p_cdh;		// 'cdhome'
 
 /*
  * "indir" values for buffer-local options.

src/optiondefs.h

@@ -549,6 +549,10 @@ static struct vimoption options[] =
 			    (char_u *)&p_cmp, PV_NONE,
 			    {(char_u *)"internal,keepascii", (char_u *)0L}
 			    SCTX_INIT},
+    {"cdhome",	    "cdh",  P_BOOL|P_VI_DEF|P_VIM|P_SECURE,
+			    (char_u *)&p_cdh, PV_NONE,
+			    {(char_u *)FALSE, (char_u *)0L}
+			    SCTX_INIT},
     {"cdpath",	    "cd",   P_STRING|P_EXPAND|P_VI_DEF|P_SECURE|P_COMMA|P_NODUP,
 #ifdef FEAT_SEARCHPATH
 			    (char_u *)&p_cdpath, PV_NONE,

src/testdir/runtest.vim

@@ -77,6 +77,9 @@ if has('reltime')
   let s:start_time = reltime()
 endif
 
+" Always use forward slashes.
+set shellslash
+
 " Common with all tests on all systems.
 source setup.vim
 
@@ -128,9 +131,6 @@ if has('gui_running') && exists('did_install_default_menus')
   source $VIMRUNTIME/menu.vim
 endif
 
-" Always use forward slashes.
-set shellslash
-
 let s:srcdir = expand('%:p:h:h')
 
 if has('win32')

src/testdir/test_options.vim

@@ -1199,4 +1199,25 @@ func Test_opt_scrolljump()
   bw
 endfunc
 
+" Test for the 'cdhome' option
+func Test_opt_cdhome()
+  if has('unix') || has('vms')
+    throw 'Skipped: only works on non-Unix'
+  endif
+
+  set cdhome&
+  call assert_equal(0, &cdhome)
+  set cdhome
+
+  " This paragraph is copied from Test_cd_no_arg().
+  let path = getcwd()
+  cd
+  call assert_equal($HOME, getcwd())
+  call assert_notequal(path, getcwd())
+  exe 'cd ' .. fnameescape(path)
+  call assert_equal(path, getcwd())
+
+  set cdhome&
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3780,
 /**/
     3779,
 /**/