vim-patch:8.2.2778: problem restoring 'packpath' in session

Problem:    Problem restoring 'packpath' in session.
Solution:   Let "skiprtp" also apply to 'packpath'.
d23b714d8b

Port Test_mksession_skiprtp() to lua functional test.

runtime/doc/options.txt

@@ -5052,7 +5052,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 			global values for local options)
 	   options	all options and mappings (also global values for local
 			options)
-	   skiprtp	exclude 'runtimepath' from the options
+	   skiprtp	exclude 'runtimepath' and 'packpath' from the options
 	   resize	size of the Vim window: 'lines' and 'columns'
 	   sesdir	the directory in which the session file is located
 			will become the current directory (useful with

src/nvim/option.c

@@ -5232,7 +5232,8 @@ int makeset(FILE *fd, int opt_flags, int local_only)
           continue;
         }
 
-        if ((opt_flags & OPT_SKIPRTP) && p->var == (char_u *)&p_rtp) {
+        if ((opt_flags & OPT_SKIPRTP)
+            && (p->var == (char_u *)&p_rtp || p->var == (char_u *)&p_pp)) {
           continue;
         }
 

test/functional/legacy/mksession_spec.lua

@@ -0,0 +1,42 @@
+local helpers = require('test.functional.helpers')(after_each)
+local clear = helpers.clear
+local command = helpers.command
+local funcs = helpers.funcs
+local eq = helpers.eq
+
+describe('mksession', function()
+  before_each(clear)
+
+  after_each(function()
+    os.remove('Xtest_mks.out')
+  end)
+
+  it('supports "skiprtp" value', function()
+    command('set sessionoptions&vi')
+    command('set rtp+=$HOME')
+    command('set pp+=$HOME')
+    command('mksession! Xtest_mks.out')
+    local found_rtp = 0
+    local found_pp = 0
+    for _, line in pairs(funcs.readfile('Xtest_mks.out', 'b')) do
+      if line:find('set runtimepath') then
+        found_rtp = found_rtp + 1
+      end
+      if line:find('set packpath') then
+        found_pp = found_pp + 1
+      end
+    end
+    eq(1, found_rtp)
+    eq(1, found_pp)
+
+    command('set sessionoptions+=skiprtp')
+    command('mksession! Xtest_mks.out')
+    local found_rtp_or_pp = 0
+    for _, line in pairs(funcs.readfile('Xtest_mks.out', 'b')) do
+      if line:find('set runtimepath') or line:find('set packpath') then
+        found_rtp_or_pp = found_rtp_or_pp + 1
+      end
+    end
+    eq(0, found_rtp_or_pp)
+  end)
+end)