feat(api): nvim_open_win() relative to tabline and laststatus #32006

Problem:  Anchoring a floating window to the tabline and laststatus is
          cumbersome; requiring autocommands and looping over all
          windows/tabpages.
Solution: Add new "tabline" and "laststatus" options to the `relative`
          field of nvim_open_win() to place a window relative to.

8 files changed, 133 insertions, 12 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index 572e5e4267..5a6361d45f 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -3150,11 +3150,13 @@ nvim_open_win({buffer}, {enter}, {config})                   *nvim_open_win()*
       • {config}  Map defining the window configuration. Keys:
                   • relative: Sets the window layout to "floating", placed at
                     (row,col) coordinates relative to:
-                    • "editor" The global editor grid
+                    • "cursor" Cursor position in current window.
+                    • "editor" The global editor grid.
+                    • "laststatus" 'laststatus' if present, or last row.
+                    • "mouse" Mouse position.
+                    • "tabline" Tabline if present, or first row.
                     • "win" Window given by the `win` field, or current
                       window.
-                    • "cursor" Cursor position in current window.
-                    • "mouse" Mouse position
                   • win: |window-ID| window to split, or relative window when
                     creating a float (relative="win").
                   • anchor: Decides which corner of the float to place at
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index 89504ae244..e6a1adf15b 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -187,6 +187,7 @@ API
 • |nvim__ns_set()| can set properties for a namespace
 • |nvim_echo()| `err` field to print error messages and `chunks` accepts
   highlight group IDs.
+• |nvim_open_win()| `relative` field can be set to "laststatus" and "tabline".
 
 DEFAULTS
 
diff --git a/runtime/lua/vim/_meta/api.lua b/runtime/lua/vim/_meta/api.lua
index 8930f131f6..670e867c1e 100644
--- a/runtime/lua/vim/_meta/api.lua
+++ b/runtime/lua/vim/_meta/api.lua
@@ -1754,10 +1754,12 @@ function vim.api.nvim_open_term(buffer, opts) end
 --- @param config vim.api.keyset.win_config Map defining the window configuration. Keys:
 --- - relative: Sets the window layout to "floating", placed at (row,col)
 ---               coordinates relative to:
----    - "editor" The global editor grid
----    - "win"    Window given by the `win` field, or current window.
----    - "cursor" Cursor position in current window.
----    - "mouse"  Mouse position
+---    - "cursor"     Cursor position in current window.
+---    - "editor"     The global editor grid.
+---    - "laststatus" 'laststatus' if present, or last row.
+---    - "mouse"      Mouse position.
+---    - "tabline"    Tabline if present, or first row.
+---    - "win"        Window given by the `win` field, or current window.
 --- - win: `window-ID` window to split, or relative window when creating a
 ---    float (relative="win").
 --- - anchor: Decides which corner of the float to place at (row,col):
diff --git a/src/nvim/api/win_config.c b/src/nvim/api/win_config.c
index 45c9e3f56c..225189a3f9 100644
--- a/src/nvim/api/win_config.c
+++ b/src/nvim/api/win_config.c
@@ -101,10 +101,12 @@
 /// @param config Map defining the window configuration. Keys:
 ///   - relative: Sets the window layout to "floating", placed at (row,col)
 ///                 coordinates relative to:
-///      - "editor" The global editor grid
-///      - "win"    Window given by the `win` field, or current window.
-///      - "cursor" Cursor position in current window.
-///      - "mouse"  Mouse position
+///      - "cursor"     Cursor position in current window.
+///      - "editor"     The global editor grid.
+///      - "laststatus" 'laststatus' if present, or last row.
+///      - "mouse"      Mouse position.
+///      - "tabline"    Tabline if present, or first row.
+///      - "win"        Window given by the `win` field, or current window.
 ///   - win: |window-ID| window to split, or relative window when creating a
 ///      float (relative="win").
 ///   - anchor: Decides which corner of the float to place at (row,col):
@@ -699,7 +701,9 @@ Dict(win_config) nvim_win_get_config(Window window, Arena *arena, Error *err)
   FUNC_API_SINCE(6)
 {
   /// Keep in sync with FloatRelative in buffer_defs.h
-  static const char *const float_relative_str[] = { "editor", "win", "cursor", "mouse" };
+  static const char *const float_relative_str[] = {
+    "editor", "win", "cursor", "mouse", "tabline", "laststatus"
+  };
 
   /// Keep in sync with WinSplit in buffer_defs.h
   static const char *const win_split_str[] = { "left", "right", "above", "below" };
@@ -805,6 +809,10 @@ static bool parse_float_relative(String relative, FloatRelative *out)
     *out = kFloatRelativeCursor;
   } else if (striequal(str, "mouse")) {
     *out = kFloatRelativeMouse;
+  } else if (striequal(str, "tabline")) {
+    *out = kFloatRelativeTabline;
+  } else if (striequal(str, "laststatus")) {
+    *out = kFloatRelativeLaststatus;
   } else {
     return false;
   }
diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index 3fe44beab9..bffb29578f 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -900,6 +900,8 @@ typedef enum {
   kFloatRelativeWindow = 1,
   kFloatRelativeCursor = 2,
   kFloatRelativeMouse = 3,
+  kFloatRelativeTabline = 4,
+  kFloatRelativeLaststatus = 5,
 } FloatRelative;
 
 /// Keep in sync with win_split_str[] in nvim_win_get_config() (api/win_config.c)
diff --git a/src/nvim/window.c b/src/nvim/window.c
index 68f45ec5ba..1c0d8c1027 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -835,6 +835,10 @@ void ui_ext_win_position(win_T *wp, bool validate)
           col += tcol - 1;
         }
       }
+    } else if (c.relative == kFloatRelativeLaststatus) {
+      row += Rows - (int)p_ch - last_stl_height(false);
+    } else if (c.relative == kFloatRelativeTabline) {
+      row += tabline_height();
     }
 
     bool resort = wp->w_grid_alloc.comp_index != 0
@@ -1066,6 +1070,7 @@ win_T *win_split_ins(int size, int flags, win_T *new_wp, int dir, frame_T *to_fl
       return NULL;
     }
     need_status = STATUS_HEIGHT;
+    win_float_anchor_laststatus();
   }
 
   bool do_equal = false;
@@ -6803,6 +6808,7 @@ void last_status(bool morewin)
 {
   // Don't make a difference between horizontal or vertical split.
   last_status_rec(topframe, last_stl_height(morewin) > 0, global_stl_height() > 0);
+  win_float_anchor_laststatus();
 }
 
 // Remove status line from window, replacing it with a horizontal separator if needed.
diff --git a/src/nvim/winfloat.c b/src/nvim/winfloat.c
index 3e791e2beb..d11b965dfc 100644
--- a/src/nvim/winfloat.c
+++ b/src/nvim/winfloat.c
@@ -307,6 +307,15 @@ void win_check_anchored_floats(win_T *win)
   }
 }
 
+void win_float_anchor_laststatus(void)
+{
+  FOR_ALL_WINDOWS_IN_TAB(win, curtab) {
+    if (win->w_config.relative == kFloatRelativeLaststatus) {
+      win->w_pos_changed = true;
+    }
+  }
+}
+
 void win_reconfig_floats(void)
 {
   for (win_T *wp = lastwin; wp && wp->w_floating; wp = wp->w_prev) {
diff --git a/test/functional/ui/float_spec.lua b/test/functional/ui/float_spec.lua
index be0a9b80cf..ca26c46fc5 100644
--- a/test/functional/ui/float_spec.lua
+++ b/test/functional/ui/float_spec.lua
@@ -1012,6 +1012,97 @@ describe('float window', function()
     end)
   end)
 
+  it('placed relative to tabline and laststatus', function()
+    local screen = Screen.new(20, 10)
+    screen:add_extra_attr_ids({ [100] = { bold = true, foreground = Screen.colors.Magenta } })
+    command('set showtabline=1 laststatus=1')
+    api.nvim_open_win(0, false, {
+      relative = 'laststatus',
+      border = 'single',
+      anchor = 'SE',
+      width = 5,
+      height = 1,
+      row = 0,
+      col = 1000,
+    })
+    local tabwin = api.nvim_open_win(0, false, {
+      relative = 'tabline',
+      border = 'single',
+      width = 5,
+      height = 1,
+      row = 0,
+      col = 1000,
+    })
+    screen:expect([[
+      ^             {2:┌─────┐}|
+      {1:~            }{2:│}{4:     }{2:│}|
+      {1:~            }{2:└─────┘}|
+      {1:~                   }|*3
+      {1:~            }{2:┌─────┐}|
+      {1:~            }{2:│}{4:     }{2:│}|
+      {1:~            }{2:└─────┘}|
+                          |
+    ]])
+    command('tabnew | tabnext')
+    screen:expect([[
+      {5: }{100:3}{5:  Name] }{24: No Name]X}|
+      ^             {2:┌─────┐}|
+      {1:~            }{2:│}{4:     }{2:│}|
+      {1:~            }{2:└─────┘}|
+      {1:~                   }|*2
+      {1:~            }{2:┌─────┐}|
+      {1:~            }{2:│}{4:     }{2:│}|
+      {1:~            }{2:└─────┘}|
+                          |
+    ]])
+    command('vsplit')
+    screen:expect([[
+      {5: }{100:4}{5:  Name] }{24: No Name]X}|
+      ^             {2:┌─────┐}|
+      {1:~            }{2:│}{4:     }{2:│}|
+      {1:~            }{2:└─────┘}|
+      {1:~                 }{2:│}{1:~}|
+      {1:~            }{2:┌─────┐}|
+      {1:~            }{2:│}{4:     }{2:│}|
+      {1:~            }{2:└─────┘}|
+      {3:[No Name]          }{2:<}|
+                          |
+    ]])
+    command('quit')
+    api.nvim_win_set_config(tabwin, {
+      relative = 'tabline',
+      border = 'single',
+      width = 5,
+      height = 1,
+      row = 1,
+      col = 0,
+    })
+    screen:expect([[
+      {5: }{100:3}{5:  Name] }{24: No Name]X}|
+      ^                    |
+      {2:┌─────┐}{1:             }|
+      {2:│}{4:     }{2:│}{1:             }|
+      {2:└─────┘}{1:             }|
+      {1:~                   }|
+      {1:~            }{2:┌─────┐}|
+      {1:~            }{2:│}{4:     }{2:│}|
+      {1:~            }{2:└─────┘}|
+                          |
+    ]])
+    command('tabonly')
+    screen:expect([[
+      ^                    |
+      {2:┌─────┐}{1:             }|
+      {2:│}{4:     }{2:│}{1:             }|
+      {2:└─────┘}{1:             }|
+      {1:~                   }|*2
+      {1:~            }{2:┌─────┐}|
+      {1:~            }{2:│}{4:     }{2:│}|
+      {1:~            }{2:└─────┘}|
+                          |
+    ]])
+  end)
+
   local function with_ext_multigrid(multigrid)
     local screen, attrs
     before_each(function()