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)
0f6b4f06de

runtime/doc/eval.txt

@@ -2377,6 +2377,7 @@ win_screenpos({nr})		List	get screen position of window {nr}
 winbufnr({nr})			Number	buffer number of window {nr}
 wincol()			Number	window column of the cursor
 winheight({nr})			Number	height of window {nr}
+winlayout([{tabnr}])		List	layout of windows in tab {tabnr}
 winline()			Number	window line of the cursor
 winnr([{expr}])			Number	number of current window
 winrestcmd()			String	returns command to restore window sizes
@@ -8537,6 +8538,35 @@ winheight({nr})						*winheight()*
 		This excludes any window toolbar line.
 		Examples: >
   :echo "The current window has " . winheight(0) . " lines."
+<
+winlayout([{tabnr}])					*winlayout()*
+		The result is a nested List containing the layout of windows
+		in a tabpage.
+
+		Without {tabnr} use the current tabpage, otherwise the tabpage
+		with number {tabnr}. If the tabpage {tabnr} is not found,
+		returns an empty list.
+
+		For a leaf window, it returns:
+			['leaf', {winid}]
+		For horizontally split windows, which form a column, it
+		returns:
+			['col', [{nested list of windows}]]
+		For vertically split windows, which form a row, it returns:
+			['row', [{nested list of windows}]]
+
+		Example: >
+			" Only one window in the tab page
+			:echo winlayout()
+			['leaf', 1000]
+			" Two horizontally split windows
+			:echo winlayout()
+			['col', [['leaf', 1000], ['leaf', 1001]]]
+			" Three horizontally split windows, with two
+			" vertically split windows in the middle window
+			:echo winlayout(2)
+			['col', [['leaf', 1002], ['row', ['leaf', 1003],
+					     ['leaf', 1001]]], ['leaf', 1000]]
 <
 							*winline()*
 winline()	The result is a Number, which is the screen line of the cursor

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
  */

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={},

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

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) {