tchdir: New tab should inherit CWD. (#5227)

When a new tabpage gets created it will copy the local working directory
of the previous one, if there is any.

src/nvim/window.c

@@ -2978,6 +2978,9 @@ int win_new_tabpage(int after, char_u *filename)
     xfree(newtp);
     return FAIL;
   }
+
+  newtp->localdir = tp->localdir ? vim_strsave(tp->localdir) : NULL;
+
   curtab = newtp;
 
   /* Create a new empty window. */

test/functional/ex_cmds/cd_spec.lua

@@ -140,6 +140,27 @@ for _, cmd in ipairs {'cd', 'chdir'} do
       end)
     end)
 
+    describe('Local directory gets inherited', function()
+      it('by tabs', function()
+        local globalDir = directories.start
+
+        -- Create a new tab and change directory
+        execute('tabnew')
+        execute('silent t' .. cmd .. ' ' .. directories.tab)
+        eq(globalDir .. '/' .. directories.tab, tcwd())
+
+        -- Create a new tab and verify it has inherited the directory
+        execute('tabnew')
+        eq(globalDir .. '/' .. directories.tab, tcwd())
+
+        -- Change tab and change back, verify that directories are correct
+        execute('tabnext')
+        eq(globalDir, tcwd())
+        execute('tabprevious')
+        eq(globalDir .. '/' .. directories.tab, tcwd())
+      end)
+    end)
+
     it('works', function()
       local globalDir = directories.start
       -- Create a new tab first and verify that is has the same working dir