mksession: Restore tab-local working directory #6859

The ':tcd' command is the first tab-specific command written to the file
and it is wrapped inside an 'if has('nvim')' block to keep the session
file compatible with Vim.

Closes #6678

src/nvim/ex_docmd.c

@@ -8847,15 +8847,16 @@ makeopens (
    */
   tab_firstwin = firstwin;      /* first window in tab page "tabnr" */
   tab_topframe = topframe;
-  for (tabnr = 1;; ++tabnr) {
+  for (tabnr = 1;; tabnr++) {
+    tabpage_T *tp = find_tabpage(tabnr);
+    if (tp == NULL) {
+      break;  // done all tab pages
+    }
+
     int need_tabnew = false;
     int cnr = 1;
 
     if ((ssop_flags & SSOP_TABPAGES)) {
-      tabpage_T *tp = find_tabpage(tabnr);
-
-      if (tp == NULL)
-        break;                  /* done all tab pages */
       if (tp == curtab) {
         tab_firstwin = firstwin;
         tab_topframe = topframe;
@@ -8968,6 +8969,16 @@ makeopens (
     if (nr > 1 && ses_winsizes(fd, restore_size, tab_firstwin) == FAIL)
       return FAIL;
 
+    // Take care of tab-local working directories if applicable
+    if (tp->tp_localdir) {
+      if (fputs("if has('nvim') | tcd ", fd) < 0
+          || ses_put_fname(fd, tp->tp_localdir, &ssop_flags) == FAIL
+          || fputs(" | endif", fd) < 0
+          || put_eol(fd) == FAIL) {
+        return FAIL;
+      }
+    }
+
     /* Don't continue in another tab page when doing only the current one
      * or when at the last tab page. */
     if (!(ssop_flags & SSOP_TABPAGES))

test/functional/ex_cmds/mksession_spec.lua

@@ -0,0 +1,49 @@
+local lfs = require('lfs')
+local helpers = require('test.functional.helpers')(after_each)
+
+local clear = helpers.clear
+local command = helpers.command
+local get_pathsep = helpers.get_pathsep
+local eq = helpers.eq
+local funcs = helpers.funcs
+
+local file_prefix = 'Xtest-functional-ex_cmds-mksession_spec'
+
+describe(':mksession', function()
+  local session_file = file_prefix .. '.vim'
+  local tab_dir = file_prefix .. '.d'
+
+  before_each(function()
+    clear()
+    lfs.mkdir(tab_dir)
+  end)
+
+  after_each(function()
+    os.remove(session_file)
+    lfs.rmdir(tab_dir)
+  end)
+
+  it('restores tab-local working directories', function()
+    local tmpfile_base = file_prefix .. '-tmpfile'
+    local cwd_dir = funcs.getcwd()
+
+    -- :mksession does not save empty tabs, so create some buffers.
+    command('edit ' .. tmpfile_base .. '1')
+    command('tabnew')
+    command('edit ' .. tmpfile_base .. '2')
+    command('tcd ' .. tab_dir)
+    command('tabfirst')
+    command('mksession ' .. session_file)
+
+    -- Create a new test instance of Nvim.
+    clear()
+
+    command('source ' .. session_file)
+    -- First tab should have the original working directory.
+    command('tabnext 1')
+    eq(cwd_dir, funcs.getcwd())
+    -- Second tab should have the tab-local working directory.
+    command('tabnext 2')
+    eq(cwd_dir .. get_pathsep() .. tab_dir, funcs.getcwd())
+  end)
+end)