vim-patch:8.1.2045: the option.c file is too big (#19854)

Problem:    The option.c file is too big.
Solution:   Split off the code dealing with strings. (Yegappan Lakshmanan,
            closes vim/vim#4937)
https://github.com/vim/vim/commit/dac1347b4d9c1a1aef6aa73fdea08a9d1077d6ea

Cherry-pick set_string_option_direct_in_win() from patch 8.1.1405.
Cherry-pick shift_line() comment change from patch 8.1.2096.
Move 'clipboard' default parsing to didset_string_options().
Reorder option flags to put Nvim-only flags at the end.

1 files changed, 28 insertions, 0 deletions

diff --git a/test/unit/optionstr_spec.lua b/test/unit/optionstr_spec.lua
new file mode 100644
index 0000000000..f8122f4fe0
--- /dev/null
+++ b/test/unit/optionstr_spec.lua
@@ -0,0 +1,28 @@
+local helpers = require("test.unit.helpers")(after_each)
+local itp = helpers.gen_itp(it)
+
+local to_cstr = helpers.to_cstr
+local eq      = helpers.eq
+
+local option = helpers.cimport("./src/nvim/optionstr.h")
+
+local check_ff_value = function(ff)
+  return option.check_ff_value(to_cstr(ff))
+end
+
+describe('check_ff_value', function()
+
+  itp('views empty string as valid', function()
+    eq(1, check_ff_value(""))
+  end)
+
+  itp('views "unix", "dos" and "mac" as valid', function()
+    eq(1, check_ff_value("unix"))
+    eq(1, check_ff_value("dos"))
+    eq(1, check_ff_value("mac"))
+  end)
+
+  itp('views "foo" as invalid', function()
+    eq(0, check_ff_value("foo"))
+  end)
+end)