fix(api): fix 'winborder' preventing splits with nvim_open_win (#32981)

While at it, rename the p_winbd variable to p_winborder, as 'winbd' is
not the option's short name.

Co-authored-by: glepnir <glephunter@gmail.com>

4 files changed, 18 insertions, 5 deletions

diff --git a/src/nvim/api/win_config.c b/src/nvim/api/win_config.c
index 31de5ca1eb..4b5b02e507 100644
--- a/src/nvim/api/win_config.c
+++ b/src/nvim/api/win_config.c
@@ -1273,13 +1273,18 @@ static bool parse_win_config(win_T *wp, Dict(win_config) *config, WinConfig *fco
     }
   }
 
-  if (HAS_KEY_X(config, border) || *p_winbd != NUL) {
+  Object border_style = OBJECT_INIT;
+  if (HAS_KEY_X(config, border)) {
     if (is_split) {
       api_set_error(err, kErrorTypeValidation, "non-float cannot have 'border'");
       goto fail;
     }
-    Object style = config->border.type != kObjectTypeNil ? config->border : CSTR_AS_OBJ(p_winbd);
-    parse_border_style(style, fconfig, err);
+    border_style = config->border;
+  } else if (*p_winborder != NUL) {
+    border_style = CSTR_AS_OBJ(p_winborder);
+  }
+  if (border_style.type != kObjectTypeNil) {
+    parse_border_style(border_style, fconfig, err);
     if (ERROR_SET(err)) {
       goto fail;
     }
diff --git a/src/nvim/option_vars.h b/src/nvim/option_vars.h
index a484eb8447..3f0445675d 100644
--- a/src/nvim/option_vars.h
+++ b/src/nvim/option_vars.h
@@ -566,7 +566,7 @@ EXTERN OptInt p_wcm;            ///< 'wildcharm'
 EXTERN int p_wic;               ///< 'wildignorecase'
 EXTERN char *p_wim;             ///< 'wildmode'
 EXTERN int p_wmnu;              ///< 'wildmenu'
-EXTERN char *p_winbd;           ///< 'winborder'
+EXTERN char *p_winborder;       ///< 'winborder'
 EXTERN OptInt p_wh;             ///< 'winheight'
 EXTERN OptInt p_wmh;            ///< 'winminheight'
 EXTERN OptInt p_wmw;            ///< 'winminwidth'
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index 6c71477ba0..bb63ff638b 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -10205,7 +10205,7 @@ local options = {
       scope = { 'global' },
       short_desc = N_('border of floating window'),
       type = 'string',
-      varname = 'p_winbd',
+      varname = 'p_winborder',
     },
     {
       abbreviation = 'wi',
diff --git a/test/functional/api/window_spec.lua b/test/functional/api/window_spec.lua
index 028f0beb38..119c185b72 100644
--- a/test/functional/api/window_spec.lua
+++ b/test/functional/api/window_spec.lua
@@ -1825,6 +1825,14 @@ describe('API/win', function()
       )
     end)
 
+    it("can create split window when 'winborder' is set", function()
+      local old_win = api.nvim_get_current_win()
+      api.nvim_set_option_value('winborder', 'single', {})
+      local new_win = api.nvim_open_win(0, false, { split = 'right', win = 0 })
+      eq({ 'row', { { 'leaf', old_win }, { 'leaf', new_win } } }, fn.winlayout())
+      eq('', api.nvim_win_get_config(new_win).relative)
+    end)
+
     describe("with 'autochdir'", function()
       local topdir
       local otherbuf