vim-patch:8.1.0307: there is no good way to get the window layout

Problem:    There is no good way to get the window layout.
Solution:   Add the winlayout() function. (Yegappan Lakshmanan)
https://github.com/vim/vim/commit/0f6b4f06dece71487a6d8546c50de775d9c8c287

4 files changed, 75 insertions, 0 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 78a6092fa1..868305c88d 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -17872,6 +17872,25 @@ static void f_winheight(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   }
 }
 
+// "winlayout()" function
+static void f_winlayout(typval_T *argvars, typval_T *rettv, FunPtr fptr)
+{
+  tabpage_T *tp;
+
+  tv_list_alloc_ret(rettv, 2);
+
+  if (argvars[0].v_type == VAR_UNKNOWN) {
+    tp = curtab;
+  } else {
+    tp = find_tabpage((int)tv_get_number(&argvars[0]));
+    if (tp == NULL) {
+      return;
+    }
+  }
+
+  get_framelayout(tp->tp_topframe, rettv->vval.v_list, true);
+}
+
 /*
  * "winline()" function
  */
diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index aad2de5d30..dea00c3edd 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -352,6 +352,7 @@ return {
     winbufnr={args=1},
     wincol={},
     winheight={args=1},
+    winlayout={args={0, 1}},
     winline={},
     winnr={args={0, 1}},
     winrestcmd={},
diff --git a/src/nvim/testdir/test_window_id.vim b/src/nvim/testdir/test_window_id.vim
index b3b506d04d..d10d831650 100644
--- a/src/nvim/testdir/test_window_id.vim
+++ b/src/nvim/testdir/test_window_id.vim
@@ -101,3 +101,23 @@ func Test_win_getid_curtab()
   call assert_equal(win_getid(1), win_getid(1, 1))
   tabclose!
 endfunc
+
+func Test_winlayout()
+  let w1 = win_getid()
+  call assert_equal(['leaf', w1], winlayout())
+
+  split
+  let w2 = win_getid()
+  call assert_equal(['col', [['leaf', w2], ['leaf', w1]]], winlayout())
+
+  split
+  let w3 = win_getid()
+  call assert_equal(['col', [['leaf', w3], ['leaf', w2], ['leaf', w1]]], winlayout())
+
+  2wincmd w
+  vsplit
+  let w4 = win_getid()
+  call assert_equal(['col', [['leaf', w3], ['row', [['leaf', w4], ['leaf', w2]]], ['leaf', w1]]], winlayout())
+
+  only!
+endfunc
diff --git a/src/nvim/window.c b/src/nvim/window.c
index 2ce3b7067b..e6b19cf88d 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -6658,6 +6658,41 @@ void win_findbuf(typval_T *argvars, list_T *list)
   }
 }
 
+// Get the layout of the given tab page for winlayout().
+void get_framelayout(const frame_T *fr, list_T *l, bool outer)
+{
+  list_T *fr_list;
+
+  if (fr == NULL) {
+    return;
+  }
+
+  if (outer) {
+    // outermost call from f_winlayout()
+    fr_list = l;
+  } else {
+    fr_list = tv_list_alloc(2);
+    tv_list_append_list(l, fr_list);
+  }
+
+  if (fr->fr_layout == FR_LEAF) {
+    if (fr->fr_win != NULL) {
+      tv_list_append_string(fr_list, "leaf", -1);
+      tv_list_append_number(fr_list, fr->fr_win->handle);
+    }
+  } else {
+    tv_list_append_string(fr_list, fr->fr_layout == FR_ROW ? "row" : "col", -1);
+
+    list_T *const win_list = tv_list_alloc(kListLenUnknown);
+    tv_list_append_list(fr_list, win_list);
+    const frame_T *child = fr->fr_child;
+    while (child != NULL) {
+      get_framelayout(child, win_list, false);
+      child = child->fr_next;
+    }
+  }
+}
+
 void win_ui_flush_positions(void)
 {
   FOR_ALL_TAB_WINDOWS(tp, wp) {