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)

runtime/doc/eval.txt

@@ -2497,6 +2497,7 @@ 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
@@ -9087,6 +9088,35 @@ 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/evalfunc.c

@@ -463,6 +463,7 @@ static void f_win_screenpos(typval_T *argvars, typval_T *rettv);
 static void f_winbufnr(typval_T *argvars, typval_T *rettv);
 static void f_wincol(typval_T *argvars, typval_T *rettv);
 static void f_winheight(typval_T *argvars, typval_T *rettv);
+static void f_winlayout(typval_T *argvars, typval_T *rettv);
 static void f_winline(typval_T *argvars, typval_T *rettv);
 static void f_winnr(typval_T *argvars, typval_T *rettv);
 static void f_winrestcmd(typval_T *argvars, typval_T *rettv);
@@ -952,6 +953,7 @@ static struct fst
     {"winbufnr",	1, 1, f_winbufnr},
     {"wincol",		0, 0, f_wincol},
     {"winheight",	1, 1, f_winheight},
+    {"winlayout",	0, 1, f_winlayout},
     {"winline",		0, 0, f_winline},
     {"winnr",		0, 1, f_winnr},
     {"winrestcmd",	0, 0, f_winrestcmd},
@@ -13742,6 +13744,29 @@ f_winheight(typval_T *argvars, typval_T *rettv)
 	rettv->vval.v_number = wp->w_height;
 }
 
+/*
+ * "winlayout()" function
+ */
+    static void
+f_winlayout(typval_T *argvars, typval_T *rettv)
+{
+    tabpage_T	*tp;
+
+    if (rettv_list_alloc(rettv) != OK)
+	return;
+
+    if (argvars[0].v_type == VAR_UNKNOWN)
+	tp = curtab;
+    else
+    {
+	tp = find_tabpage((int)get_tv_number(&argvars[0]));
+	if (tp == NULL)
+	    return;
+    }
+
+    get_framelayout(tp->tp_topframe, rettv->vval.v_list, TRUE);
+}
+
 /*
  * "winline()" function
  */

src/proto/window.pro

@@ -94,4 +94,5 @@ void win_id2tabwin(typval_T *argvars, list_T *list);
 win_T *win_id2wp(typval_T *argvars);
 int win_id2win(typval_T *argvars);
 void win_findbuf(typval_T *argvars, list_T *list);
+void get_framelayout(frame_T *fr, list_T *l, int topframe);
 /* vim: set ft=c : */

src/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/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    307,
 /**/
     306,
 /**/

src/window.c

@@ -7236,4 +7236,53 @@ win_findbuf(typval_T *argvars, list_T *list)
 		list_append_number(list, wp->w_id);
 }
 
+/*
+ * Get the layout of the given tab page for winlayout().
+ */
+    void
+get_framelayout(frame_T *fr, list_T *l, int outer)
+{
+    frame_T	*child;
+    list_T	*fr_list;
+    list_T	*win_list;
+
+    if (fr == NULL)
+	return;
+
+    if (outer)
+	// outermost call from f_winlayout()
+	fr_list = l;
+    else
+    {
+	fr_list = list_alloc();
+	if (fr_list == NULL)
+	    return;
+	list_append_list(l, fr_list);
+    }
+
+    if (fr->fr_layout == FR_LEAF)
+    {
+	if (fr->fr_win != NULL)
+	{
+	    list_append_string(fr_list, (char_u *)"leaf", -1);
+	    list_append_number(fr_list, fr->fr_win->w_id);
+	}
+    }
+    else
+    {
+	list_append_string(fr_list,
+	     fr->fr_layout == FR_ROW ?  (char_u *)"row" : (char_u *)"col", -1);
+
+	win_list = list_alloc();
+	if (win_list == NULL)
+	    return;
+	list_append_list(fr_list, win_list);
+	child = fr->fr_child;
+	while (child != NULL)
+	{
+	    get_framelayout(child, win_list, FALSE);
+	    child = child->fr_next;
+	}
+    }
+}
 #endif