feat(api): add nvim_tabpage_set_win (#27222)

Allows setting the current window of a non-current tabpage
without switching tabpages.

6 files changed, 103 insertions, 1 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index 90c9d0ccbb..1831b78e9e 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -3336,6 +3336,13 @@ nvim_tabpage_set_var({tabpage}, {name}, {value})
       • {name}     Variable name
       • {value}    Variable value
 
+nvim_tabpage_set_win({tabpage}, {win})                *nvim_tabpage_set_win()*
+    Sets the current window in a tabpage
+
+    Parameters: ~
+      • {tabpage}  Tabpage handle, or 0 for current tabpage
+      • {win}      Window handle, must already belong to {tabpage}
+
 
 ==============================================================================
 Autocmd Functions                                                *api-autocmd*
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index 40717f8ecf..3051b81189 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -304,6 +304,8 @@ The following new APIs and features were added.
   highlight attribute. The TUI will display URLs using the OSC 8 control
   sequence, enabling clickable text in supporting terminals.
 
+• Added |nvim_tabpage_set_win()| to set the current window of a tabpage.
+
 ==============================================================================
 CHANGED FEATURES                                                 *news-changed*
 
diff --git a/runtime/lua/vim/_meta/api.lua b/runtime/lua/vim/_meta/api.lua
index f9fa364158..bedc218626 100644
--- a/runtime/lua/vim/_meta/api.lua
+++ b/runtime/lua/vim/_meta/api.lua
@@ -1952,6 +1952,12 @@ function vim.api.nvim_tabpage_list_wins(tabpage) end
 --- @param value any Variable value
 function vim.api.nvim_tabpage_set_var(tabpage, name, value) end
 
+--- Sets the current window in a tabpage
+---
+--- @param tabpage integer Tabpage handle, or 0 for current tabpage
+--- @param win integer Window handle, must already belong to {tabpage}
+function vim.api.nvim_tabpage_set_win(tabpage, win) end
+
 --- Calls a function with window as temporary current window.
 ---
 --- @param window integer Window handle, or 0 for current window
diff --git a/src/nvim/api/tabpage.c b/src/nvim/api/tabpage.c
index 303f2ca817..fadc03b3e5 100644
--- a/src/nvim/api/tabpage.c
+++ b/src/nvim/api/tabpage.c
@@ -122,6 +122,37 @@ Window nvim_tabpage_get_win(Tabpage tabpage, Error *err)
   abort();
 }
 
+/// Sets the current window in a tabpage
+///
+/// @param tabpage  Tabpage handle, or 0 for current tabpage
+/// @param win Window handle, must already belong to {tabpage}
+/// @param[out] err Error details, if any
+void nvim_tabpage_set_win(Tabpage tabpage, Window win, Error *err)
+  FUNC_API_SINCE(12)
+{
+  tabpage_T *tp = find_tab_by_handle(tabpage, err);
+  if (!tp) {
+    return;
+  }
+
+  win_T *wp = find_window_by_handle(win, err);
+  if (!wp) {
+    return;
+  }
+
+  if (!tabpage_win_valid(tp, wp)) {
+    api_set_error(err, kErrorTypeException, "Window does not belong to tabpage %d", tp->handle);
+    return;
+  }
+
+  if (tp == curtab) {
+    win_enter(wp, true);
+  } else if (tp->tp_curwin != wp) {
+    tp->tp_prevwin = tp->tp_curwin;
+    tp->tp_curwin = wp;
+  }
+}
+
 /// Gets the tabpage number
 ///
 /// @param tabpage  Tabpage handle, or 0 for current tabpage
diff --git a/src/nvim/window.c b/src/nvim/window.c
index 65db25bc13..66169bcb74 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -1557,7 +1557,7 @@ bool win_valid(const win_T *win) FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
 /// Check if "win" is a pointer to an existing window in tabpage "tp".
 ///
 /// @param  win  window to check
-static bool tabpage_win_valid(const tabpage_T *tp, const win_T *win)
+bool tabpage_win_valid(const tabpage_T *tp, const win_T *win)
   FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
 {
   if (win == NULL) {
diff --git a/test/functional/api/tabpage_spec.lua b/test/functional/api/tabpage_spec.lua
index f801c55de9..36955c4ace 100644
--- a/test/functional/api/tabpage_spec.lua
+++ b/test/functional/api/tabpage_spec.lua
@@ -32,6 +32,62 @@ describe('api/tabpage', function()
     end)
   end)
 
+  describe('set_win', function()
+    it('works', function()
+      command('tabnew')
+      command('vsplit')
+      local tab1, tab2 = unpack(api.nvim_list_tabpages())
+      local win1, win2, win3 = unpack(api.nvim_list_wins())
+      eq({ win1 }, api.nvim_tabpage_list_wins(tab1))
+      eq({ win2, win3 }, api.nvim_tabpage_list_wins(tab2))
+      eq(win2, api.nvim_tabpage_get_win(tab2))
+      api.nvim_tabpage_set_win(tab2, win3)
+      eq(win3, api.nvim_tabpage_get_win(tab2))
+    end)
+
+    it('works in non-current tabpages', function()
+      command('tabnew')
+      command('vsplit')
+      local tab1, tab2 = unpack(api.nvim_list_tabpages())
+      local win1, win2, win3 = unpack(api.nvim_list_wins())
+      eq({ win1 }, api.nvim_tabpage_list_wins(tab1))
+      eq({ win2, win3 }, api.nvim_tabpage_list_wins(tab2))
+      eq(win2, api.nvim_tabpage_get_win(tab2))
+      eq(win2, api.nvim_get_current_win())
+
+      command('tabprev')
+
+      eq(tab1, api.nvim_get_current_tabpage())
+
+      eq(win2, api.nvim_tabpage_get_win(tab2))
+      api.nvim_tabpage_set_win(tab2, win3)
+      eq(win3, api.nvim_tabpage_get_win(tab2))
+
+      command('tabnext')
+      eq(win3, api.nvim_get_current_win())
+    end)
+
+    it('throws an error when the window does not belong to the tabpage', function()
+      command('tabnew')
+      command('vsplit')
+      local tab1, tab2 = unpack(api.nvim_list_tabpages())
+      local win1, win2, win3 = unpack(api.nvim_list_wins())
+      eq({ win1 }, api.nvim_tabpage_list_wins(tab1))
+      eq({ win2, win3 }, api.nvim_tabpage_list_wins(tab2))
+      eq(win2, api.nvim_get_current_win())
+
+      eq(
+        string.format('Window does not belong to tabpage %d', tab2),
+        pcall_err(api.nvim_tabpage_set_win, tab2, win1)
+      )
+
+      eq(
+        string.format('Window does not belong to tabpage %d', tab1),
+        pcall_err(api.nvim_tabpage_set_win, tab1, win3)
+      )
+    end)
+  end)
+
   describe('{get,set,del}_var', function()
     it('works', function()
       api.nvim_tabpage_set_var(0, 'lua', { 1, 2, { ['3'] = 1 } })