feat: defaults: auto-create backup dir

Copy the behavior of 'undodir' and create the last specified directory
in the 'backupdir' option if it doesn't exist.

Use trailing slashes for 'backupdir' as well as 'viewdir' and 'undodir'
by default. Note that 'undodir' always behaves as though it has the
trailing slashes, regardless of whether or not they are present. They
are added to the default option value to minimize surprise.

The '.' value in 'backupdir' is kept because the default behavior for
backups is solely to have a backup if the save of the main file to disk
fails. As soon as that save is completed the backup file is removed, so
generally there is no need to put them in a central location.

Co-authored by: murphy66 <murphy66@gmail.com>

5 files changed, 39 insertions, 21 deletions

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 364d4c5167..48fdf66d7b 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -824,7 +824,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	again not rename the file.
 
 						*'backupdir'* *'bdir'*
-'backupdir' 'bdir'	string	(default ".,$XDG_DATA_HOME/nvim/backup")
+'backupdir' 'bdir'	string	(default ".,$XDG_DATA_HOME/nvim/backup//")
 			global
 	List of directories for the backup file, separated with commas.
 	- The backup file will be created in the first directory in the list
@@ -6533,7 +6533,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 'ttyfast' 'tf'		Removed. |vim-differences|
 
 						*'undodir'* *'udir'* *E5003*
-'undodir' 'udir'	string	(default "$XDG_DATA_HOME/nvim/undo")
+'undodir' 'udir'	string	(default "$XDG_DATA_HOME/nvim/undo//")
 			global
 	List of directory names for undo files, separated with commas.
 	See |'backupdir'| for details of the format.
@@ -6692,7 +6692,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	displayed when 'verbosefile' is set.
 
 						*'viewdir'* *'vdir'*
-'viewdir' 'vdir'	string	(default: "$XDG_DATA_HOME/nvim/view")
+'viewdir' 'vdir'	string	(default: "$XDG_DATA_HOME/nvim/view//")
 			global
 	Name of the directory where to store files for |:mkview|.
 	This option cannot be set from a |modeline| or in the |sandbox|, for
diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index 166c0c17aa..918b35439d 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -30,7 +30,7 @@ the differences.
 - 'autoread' is enabled
 - 'background' defaults to "dark" (unless set automatically by the terminal/UI)
 - 'backspace' defaults to "indent,eol,start"
-- 'backupdir' defaults to .,~/.local/share/nvim/backup (|xdg|)
+- 'backupdir' defaults to .,~/.local/share/nvim/backup// (|xdg|), auto-created
 - 'belloff' defaults to "all"
 - 'compatible' is always disabled
 - 'complete' excludes "i"
@@ -63,7 +63,7 @@ the differences.
 - 'tags' defaults to "./tags;,tags"
 - 'ttimeoutlen' defaults to 50
 - 'ttyfast' is always set
-- 'undodir' defaults to ~/.local/share/nvim/undo (|xdg|), auto-created
+- 'undodir' defaults to ~/.local/share/nvim/undo// (|xdg|), auto-created
 - 'viewoptions' includes "unix,slash", excludes "options"
 - 'viminfo' includes "!"
 - 'wildmenu' is enabled
diff --git a/src/nvim/fileio.c b/src/nvim/fileio.c
index 3d058e1d09..5099b3e812 100644
--- a/src/nvim/fileio.c
+++ b/src/nvim/fileio.c
@@ -2689,6 +2689,15 @@ buf_write(
          * Isolate one directory name, using an entry in 'bdir'.
          */
         (void)copy_option_part(&dirp, IObuff, IOSIZE, ",");
+        if (*dirp == NUL && !os_isdir(IObuff)) {
+          int ret;
+          char *failed_dir;
+          if ((ret = os_mkdir_recurse((char *)IObuff, 0755, &failed_dir)) != 0) {
+            EMSG3(_("E303: Unable to create directory \"%s\" for backup file: %s"),
+                  failed_dir, os_strerror(ret));
+            xfree(failed_dir);
+          }
+        }
         p = IObuff + STRLEN(IObuff);
         if (after_pathsep((char *)IObuff, (char *)p) && p[-1] == p[-2]) {
           // Ends with '//', Use Full path
@@ -2841,6 +2850,15 @@ nobackup:
          * Isolate one directory name and make the backup file name.
          */
         (void)copy_option_part(&dirp, IObuff, IOSIZE, ",");
+        if (*dirp == NUL && !os_isdir(IObuff)) {
+          int ret;
+          char *failed_dir;
+          if ((ret = os_mkdir_recurse((char *)IObuff, 0755, &failed_dir)) != 0) {
+            EMSG3(_("E303: Unable to create directory \"%s\" for backup file: %s"),
+                  failed_dir, os_strerror(ret));
+            xfree(failed_dir);
+          }
+        }
         p = IObuff + STRLEN(IObuff);
         if (after_pathsep((char *)IObuff, (char *)p) && p[-1] == p[-2]) {
           // path ends with '//', use full path
diff --git a/src/nvim/option.c b/src/nvim/option.c
index f7635fe5ec..d11bbc8ecc 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -483,17 +483,17 @@ void set_init_1(bool clean_arg)
 #endif
                      false);
 
-  char *backupdir = stdpaths_user_data_subpath("backup", 0, true);
+  char *backupdir = stdpaths_user_data_subpath("backup", 2, true);
   const size_t backupdir_len = strlen(backupdir);
   backupdir = xrealloc(backupdir, backupdir_len + 3);
   memmove(backupdir + 2, backupdir, backupdir_len + 1);
   memmove(backupdir, ".,", 2);
-  set_string_default("viewdir", stdpaths_user_data_subpath("view", 0, true),
-                     true);
   set_string_default("backupdir", backupdir, true);
+  set_string_default("viewdir", stdpaths_user_data_subpath("view", 2, true),
+                     true);
   set_string_default("directory", stdpaths_user_data_subpath("swap", 2, true),
                      true);
-  set_string_default("undodir", stdpaths_user_data_subpath("undo", 0, true),
+  set_string_default("undodir", stdpaths_user_data_subpath("undo", 2, true),
                      true);
   // Set default for &runtimepath. All necessary expansions are performed in
   // this function.
diff --git a/test/functional/options/defaults_spec.lua b/test/functional/options/defaults_spec.lua
index eb5e284385..bd3553ec59 100644
--- a/test/functional/options/defaults_spec.lua
+++ b/test/functional/options/defaults_spec.lua
@@ -354,13 +354,13 @@ describe('XDG-based defaults', function()
           .. ',' .. root_path .. ('/a'):rep(2048) .. '/nvim/after'
           .. ',' .. root_path .. ('/x'):rep(4096) .. '/nvim/after'
       ):gsub('\\', '/')), (meths.get_option('runtimepath')):gsub('\\', '/'))
-      eq('.,' .. root_path .. ('/X'):rep(4096).. '/' .. data_dir .. '/backup',
+      eq('.,' .. root_path .. ('/X'):rep(4096).. '/' .. data_dir .. '/backup//',
          (meths.get_option('backupdir'):gsub('\\', '/')))
       eq(root_path .. ('/X'):rep(4096) .. '/' .. data_dir .. '/swap//',
          (meths.get_option('directory')):gsub('\\', '/'))
-      eq(root_path .. ('/X'):rep(4096) .. '/' .. data_dir .. '/undo',
+      eq(root_path .. ('/X'):rep(4096) .. '/' .. data_dir .. '/undo//',
          (meths.get_option('undodir')):gsub('\\', '/'))
-      eq(root_path .. ('/X'):rep(4096) .. '/'  ..  data_dir .. '/view',
+      eq(root_path .. ('/X'):rep(4096) .. '/'  ..  data_dir .. '/view//',
          (meths.get_option('viewdir')):gsub('\\', '/'))
     end)
   end)
@@ -404,13 +404,13 @@ describe('XDG-based defaults', function()
           .. ',$XDG_DATA_DIRS/nvim/after'
           .. ',$XDG_DATA_HOME/nvim/after'
       ):gsub('\\', '/')), (meths.get_option('runtimepath')):gsub('\\', '/'))
-      eq(('.,$XDG_CONFIG_HOME/' .. data_dir .. '/backup'),
+      eq(('.,$XDG_CONFIG_HOME/' .. data_dir .. '/backup//'),
           meths.get_option('backupdir'):gsub('\\', '/'))
       eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/swap//'),
           meths.get_option('directory'):gsub('\\', '/'))
-      eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/undo'),
+      eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/undo//'),
           meths.get_option('undodir'):gsub('\\', '/'))
-      eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/view'),
+      eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/view//'),
           meths.get_option('viewdir'):gsub('\\', '/'))
       meths.command('set all&')
       eq(('$XDG_DATA_HOME/nvim'
@@ -424,13 +424,13 @@ describe('XDG-based defaults', function()
           .. ',$XDG_DATA_DIRS/nvim/after'
           .. ',$XDG_DATA_HOME/nvim/after'
       ):gsub('\\', '/'), (meths.get_option('runtimepath')):gsub('\\', '/'))
-      eq(('.,$XDG_CONFIG_HOME/' .. data_dir .. '/backup'),
+      eq(('.,$XDG_CONFIG_HOME/' .. data_dir .. '/backup//'),
           meths.get_option('backupdir'):gsub('\\', '/'))
       eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/swap//'),
           meths.get_option('directory'):gsub('\\', '/'))
-      eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/undo'),
+      eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/undo//'),
           meths.get_option('undodir'):gsub('\\', '/'))
-      eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/view'),
+      eq(('$XDG_CONFIG_HOME/' .. data_dir .. '/view//'),
           meths.get_option('viewdir'):gsub('\\', '/'))
     end)
   end)
@@ -483,13 +483,13 @@ describe('XDG-based defaults', function()
           .. ',\\,-\\,-\\,' .. path_sep ..'nvim' .. path_sep ..'after'
           .. ',\\, \\, \\,' .. path_sep ..'nvim' .. path_sep ..'after'
       ), meths.get_option('runtimepath'))
-      eq('.,\\,=\\,=\\,' .. path_sep .. data_dir .. '' .. path_sep ..'backup',
+      eq('.,\\,=\\,=\\,' .. path_sep .. data_dir .. '' .. path_sep ..'backup' .. (path_sep):rep(2),
           meths.get_option('backupdir'))
       eq('\\,=\\,=\\,' .. path_sep ..'' .. data_dir .. '' .. path_sep ..'swap' .. (path_sep):rep(2),
           meths.get_option('directory'))
-      eq('\\,=\\,=\\,' .. path_sep ..'' .. data_dir .. '' .. path_sep ..'undo',
+      eq('\\,=\\,=\\,' .. path_sep ..'' .. data_dir .. '' .. path_sep ..'undo' .. (path_sep):rep(2),
           meths.get_option('undodir'))
-      eq('\\,=\\,=\\,' .. path_sep ..'' .. data_dir .. '' .. path_sep ..'view',
+      eq('\\,=\\,=\\,' .. path_sep ..'' .. data_dir .. '' .. path_sep ..'view' .. (path_sep):rep(2),
           meths.get_option('viewdir'))
     end)
   end)