Empty first tab lost when using sessions

Question

I'm creating a session with mksession, and when I restore the session, if the first tab was empty ([No Name]), it's gone in the restored session. Other empty tabs are restored fine; it seems to only be the first tab that's lost. If there are multiple "leading" empty tabs, it's still only the first one that disappears.

I'm using this with vim -u NONE so there is zero config and no plugins, but I get the same behavior with my normal config. Affects versions 7.3 and 8.0.52.

I'm using the default sessionoptions in all cases: blank,buffers,curdir,folds,options,tabpages,winsize.

Steps to reproduce:

• $ vim -u NONE
• :tabnew
• :e foo.txt
• :w
• :tabnew
• :mksession
• :qa
• $ vim -u NONE -S Session.vim

The tabline now shows foo.txt | [No Name]. Expected [No Name] | foo.txt | [No Name].

Is this a known issue? Is there a workaround?

Answer 1

This is indeed a bug in Vim. I filed a GitHub issue, and someone on the vim-dev mailing list addressed it.

Here's a patch that fixes it in Vim 8.0.52:

diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 439467c..ca4133a 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -11091,6 +11091,8 @@ makeopens(
        }
        if (tabnr > 1)
        need_tabnew = TRUE;
+       else if (put_line(fd, "new") == FAIL)
+       return FAIL;
    }

    /*

Patch courtesy Hirohito Higashi on the vim-dev mailing list. I imagine it will make its way into the official distribution.

Update:

This was fixed in Vim 8.1.0149 (see GitHub PR).