vim-patch:8.1.0251: support full paths for 'backupdir' #11269

Problem:    Using a full path is supported for 'directory' but not for
            'backupdir'. (Mikolaj Machowski)
Solution:   Support 'backupdir' as well. (Christian Brabandt, closes vim/vim#179)
b782ba475a

test/functional/core/fileio_spec.lua

@@ -9,9 +9,12 @@ local nvim_prog = helpers.nvim_prog
 local request = helpers.request
 local retry = helpers.retry
 local rmdir = helpers.rmdir
+local mkdir = helpers.mkdir
 local sleep = helpers.sleep
 local read_file = helpers.read_file
 local trim = helpers.trim
+local currentdir = helpers.funcs.getcwd
+local iswin = helpers.iswin
 
 describe('fileio', function()
   before_each(function()
@@ -24,6 +27,7 @@ describe('fileio', function()
     os.remove('Xtest_startup_file2')
     os.remove('Xtest_тест.md')
     rmdir('Xtest_startup_swapdir')
+    rmdir('Xtest_backupdir')
   end)
 
   it('fsync() codepaths #8304', function()
@@ -88,6 +92,27 @@ describe('fileio', function()
     eq('foo', bar_contents);
   end)
 
+  it('backup with full path #11214', function()
+    clear()
+    mkdir('Xtest_backupdir')
+    command('set backup')
+    command('set backupdir=Xtest_backupdir//')
+    command('write Xtest_startup_file1')
+    feed('ifoo<esc>')
+    command('write')
+    feed('Abar<esc>')
+    command('write')
+
+    -- Backup filename = fullpath, separators replaced with "%".
+    local backup_file_name = string.gsub(currentdir()..'/Xtest_startup_file1',
+      iswin() and '[:/\\]' or '/', '%%') .. '~'
+    local foo_contents = trim(read_file('Xtest_backupdir/'..backup_file_name))
+    local foobar_contents = trim(read_file('Xtest_startup_file1'))
+
+    eq('foobar', foobar_contents);
+    eq('foo', foo_contents);
+  end)
+
   it('readfile() on multibyte filename #10586', function()
     clear()
     local text = {