feat(float): add winborder option (#31074)

Problem:
There is currently no global option to define the default border style for floating windows. This leads to repetitive code when developers need consistent styling across multiple floating windows.

Solution:
Introduce a global option winborder to specify the default border style for floating windows. When a floating window is created without explicitly specifying a border style, the value of the winborder option will be used. This simplifies configuration and ensures consistency in floating window appearance.

Co-authored-by: Gregory Anders <greg@gpanders.com>

1 files changed, 247 insertions, 0 deletions

diff --git a/test/functional/ui/float_spec.lua b/test/functional/ui/float_spec.lua
index 6610d25afb..fa4937cec3 100644
--- a/test/functional/ui/float_spec.lua
+++ b/test/functional/ui/float_spec.lua
@@ -9909,6 +9909,253 @@ describe('float window', function()
       ]])
       eq({"%f", ""}, res)
     end)
+
+    it('winborder option', function()
+      local buf = api.nvim_create_buf(false,false)
+      local config = {relative='editor', width=4, height=4, row=2, col=2}
+      command('set winborder=single')
+      api.nvim_open_win(buf, true, config)
+      if multigrid then
+        screen:expect({
+          grid = [[
+          ## grid 1
+            [2:----------------------------------------]|*6
+            [3:----------------------------------------]|
+          ## grid 2
+                                                    |
+            {0:~                                       }|*5
+          ## grid 3
+                                                    |
+          ## grid 4
+            {5:┌────┐}|
+            {5:│}{1:^    }{5:│}|
+            {5:│}{2:~   }{5:│}|*3
+            {5:└────┘}|
+          ]], float_pos={
+          [4] = {1001, "NW", 1, 2, 2, true, 50};
+        }, win_viewport={
+          [2] = {win = 1000, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+          [4] = {win = 1001, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+        }, win_viewport_margins={
+          [2] = {
+            bottom = 0,
+            left = 0,
+            right = 0,
+            top = 0,
+            win = 1000
+          },
+          [4] = {
+            bottom = 1,
+            left = 1,
+            right = 1,
+            top = 1,
+            win = 1001
+          }
+        }
+        })
+      else
+        screen:expect({
+          grid = [[
+              {5:┌────┐}                                |
+            {0:~ }{5:│}{1:^    }{5:│}{0:                                }|
+            {0:~ }{5:│}{2:~   }{5:│}{0:                                }|*3
+            {0:~ }{5:└────┘}{0:                                }|
+                                                    |
+          ]]
+        })
+      end
+      command('fclose')
+
+      command('set winborder=double')
+      api.nvim_open_win(buf, true, config)
+      if multigrid then
+        screen:expect({
+          grid = [[
+          ## grid 1
+            [2:----------------------------------------]|*6
+            [3:----------------------------------------]|
+          ## grid 2
+                                                    |
+            {0:~                                       }|*5
+          ## grid 3
+                                                    |
+          ## grid 5
+            {5:╔════╗}|
+            {5:║}{1:^    }{5:║}|
+            {5:║}{2:~   }{5:║}|*3
+            {5:╚════╝}|
+          ]], float_pos={
+          [5] = {1002, "NW", 1, 2, 2, true, 50};
+        }, win_viewport={
+          [2] = {win = 1000, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+          [5] = {win = 1002, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+        }, win_viewport_margins={
+          [2] = {
+            bottom = 0,
+            left = 0,
+            right = 0,
+            top = 0,
+            win = 1000
+          },
+          [5] = {
+            bottom = 1,
+            left = 1,
+            right = 1,
+            top = 1,
+            win = 1002
+          }
+        }
+        })
+      else
+        screen:expect({
+          grid = [[
+              {5:╔════╗}                                |
+            {0:~ }{5:║}{1:^    }{5:║}{0:                                }|
+            {0:~ }{5:║}{2:~   }{5:║}{0:                                }|*3
+            {0:~ }{5:╚════╝}{0:                                }|
+                                                    |
+          ]]
+        })
+      end
+      command('fclose!')
+
+      command('set winborder=none')
+      api.nvim_buf_set_lines(buf, 0, -1, false, {'none border'})
+      api.nvim_open_win(buf, true, config)
+      if multigrid then
+        screen:expect({
+          grid = [[
+          ## grid 1
+            [2:----------------------------------------]|*6
+            [3:----------------------------------------]|
+          ## grid 2
+                                                    |
+            {0:~                                       }|*5
+          ## grid 3
+                                                    |
+          ## grid 6
+            {1:^none}|
+            {1: bor}|
+            {1:der }|
+            {2:~   }|
+          ]],
+          win_pos = {
+          [2] = {
+            height = 6,
+            startcol = 0,
+            startrow = 0,
+            width = 40,
+            win = 1000
+          }
+        },
+          float_pos = {
+          [6] = {1003, "NW", 1, 2, 2, true, 50};
+        },
+          win_viewport = {
+          [2] = {win = 1000, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+          [6] = {win = 1003, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+        },
+          win_viewport_margins = {
+          [2] = {
+            bottom = 0,
+            left = 0,
+            right = 0,
+            top = 0,
+            win = 1000
+          },
+          [6] = {
+            bottom = 0,
+            left = 0,
+            right = 0,
+            top = 0,
+            win = 1003
+          }
+        },
+        })
+      else
+        screen:expect([[
+                                                  |
+          {0:~                                       }|
+          {0:~ }{1:^none}{0:                                  }|
+          {0:~ }{1: bor}{0:                                  }|
+          {0:~ }{1:der }{0:                                  }|
+          {0:~ }{2:~   }{0:                                  }|
+                                                  |
+        ]])
+      end
+      command('fclose!')
+
+      -- respect config.border
+      command('set winborder=rounded')
+      config.border = 'single'
+      api.nvim_open_win(buf, false, config)
+      if multigrid then
+        screen:expect({
+          grid = [[
+          ## grid 1
+            [2:----------------------------------------]|*6
+            [3:----------------------------------------]|
+          ## grid 2
+            ^                                        |
+            {0:~                                       }|*5
+          ## grid 3
+                                                    |
+          ## grid 7
+            {5:┌────┐}|
+            {5:│}{1:none}{5:│}|
+            {5:│}{1: bor}{5:│}|
+            {5:│}{1:der }{5:│}|
+            {5:│}{2:~   }{5:│}|
+            {5:└────┘}|
+          ]],
+          win_pos = {
+          [2] = {
+            height = 6,
+            startcol = 0,
+            startrow = 0,
+            width = 40,
+            win = 1000
+          }
+        },
+          float_pos = {
+          [7] = {1004, "NW", 1, 2, 2, true, 50};
+        },
+          win_viewport = {
+          [2] = {win = 1000, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+          [7] = {win = 1004, topline = 0, botline = 2, curline = 0, curcol = 0, linecount = 1, sum_scroll_delta = 0};
+        },
+          win_viewport_margins = {
+          [2] = {
+            bottom = 0,
+            left = 0,
+            right = 0,
+            top = 0,
+            win = 1000
+          },
+          [7] = {
+            bottom = 1,
+            left = 1,
+            right = 1,
+            top = 1,
+            win = 1004
+          }
+        },
+        })
+      else
+        screen:expect([[
+          ^  {5:┌────┐}                                |
+          {0:~ }{5:│}{1:none}{5:│}{0:                                }|
+          {0:~ }{5:│}{1: bor}{5:│}{0:                                }|
+          {0:~ }{5:│}{1:der }{5:│}{0:                                }|
+          {0:~ }{5:│}{2:~   }{5:│}{0:                                }|
+          {0:~ }{5:└────┘}{0:                                }|
+                                                  |
+        ]])
+      end
+
+      -- it is currently not supported.
+      eq('Vim(set):E474: Invalid argument: winborder=custom', pcall_err(command, 'set winborder=custom'))
+    end)
   end
 
   describe('with ext_multigrid', function()