Problem:    Empty group in 'tabline' may cause using an invalid pointer.
Solution:   Set the group start position. (closes vim/vim#6505)
https://github.com/vim/vim/commit/f56c95fdad5af521887f8cd7bc15729b5355231d
(cherry picked from commit 9443d3994190943c2b9d8c4efefcf3de854ec7be)

sattr_T was defined as uint16_t. But this is not enough to handle the
24-bit colors of the terminal. To solve this problem, change it to int.
In 32bit, int may overflow. So, if it overflows, change it to ignore it
without adding more attr_entries.

fixes #12366

(cherry picked from commit 872ecf65d10f0d22bbf3e2257f9ae89a6c61d2f4)

Zero out the caller's FileInfo in all the functions which populate the
struct.  The contents are considered private, so we need to ensure
it's initialized.

If the stat call fails, the buffer we get back from libuv may not have
any valid data in it, so don't copy it into the caller's FileInfo.

This was happening, expectedly, in functional/ex_cmds/write_spec.lua's
"write errors out correctly", which caused it to fail in certain
environments:

    test/functional/ex_cmds/write_spec.lua:130: Expected objects to be the same.
    Passed in:
    (string) 'Vim(write):E212: Can't open file for writing: not a directory'
    Expected:
    (string) 'Vim(write):E166: Can't open linked file for writing'

In the case of recoverymode, the headlessmode was true, causing the UI
to hang without starting. Fix this problem by setting headlessmode to
true for List swap files only.

Co-authored-by: erw7 <erw7.github@gmail.com>

* fixed hang issue with --headless and -r option specified

Calling the do_more_prompt function in headless mode will freeze neovim because it is eventally in the input-accepting state (the same as waiting for --more--).

* fixed "Press ENTER or type command to continue" to be suppressed

If in headless mode, we need to exit at this point. If we continue, we will enter the normal mode and the message "Press ENTER or type command to continue" will be displayed and we will be in the input waiting state.

* fixed functional ex_cmds tests

* Revert "fixed "Press ENTER or type command to continue" to be suppressed"

This reverts commit a02dc40e3b3fad69cedcde6abe1bd4efe39ab102.

* Revert "fixed functional ex_cmds tests"

This reverts commit 3bdb8da20acf34673b2c2028d15e7ce6da4c792a.

* fixed conditional again

* added test for fixed hang issue with --headless (#11386)

(cherry picked from commit c6dc397801d0566b583d4916220a60f17e609e25)

fix #8075

As gcc10 uses -fno-common by default, global variables declared with the
same name more than once is not allowed anymore revealing this issue.

We need to define it as extern to access it.

See also https://bugzilla.redhat.com/show_bug.cgi?id=1799680

gcc10 builds with -fno-common by default. This mean you can't define
a global variable with the same name twice.

See also https://bugzilla.redhat.com/show_bug.cgi?id=1799680

Instead of declaring an enum, this creates a global variable. As gcc10
uses -fno-common by default, global variables declared with the same
name more than once is not allowed anymore revealing this issue.

Each time this header is included, we define the enum name as a global
variable.

See also https://bugzilla.redhat.com/show_bug.cgi?id=1799680