patch 9.1.0990: Inconsistent behavior when changing cmdheight

Problem:  Inconsistent behavior when changing cmdheight by resizing the
          topframe through wincmds and dragging laststatus. Changing
	  cmdheight by resizing the topframe does not trigger OptionSet.
Solution: Consolidate logic for changing the cmdheight, set the option
	  value to handle side-effects (Luuk van Baal)

closes: #16359

Signed-off-by: Luuk van Baal <luukvbaal@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: luukvbaal

src/testdir/dumps/Test_changing_cmdheight_1.dump

@@ -5,4 +5,4 @@
 | +0&&@74
 @75
 @75
-|:|r|e|s|i|z|e| |-|3| @64
+@75

src/testdir/dumps/Test_changing_cmdheight_2.dump

@@ -1,8 +1,8 @@
 > +0&#ffffff0@74
 |~+0#4040ff13&| @73
-|~| @73
 |[+3#0000000&|N|o| |N|a|m|e|]| @47|0|,|0|-|1| @9|A|l@1
-|:+0&&|s|e|t| |c|m|d|h|e|i|g|h|t|+|=|3| @57
+| +0&&@74
+@75
 @75
 @75
 @75

src/testdir/test_autocmd.vim

@@ -4902,4 +4902,28 @@ func Test_autocmd_BufWinLeave_with_vsp()
   exe "bw! " .. dummy
 endfunc
 
+func Test_OptionSet_cmdheight()
+  set mouse=a laststatus=2
+  au OptionSet cmdheight :let &l:ch = v:option_new
+
+  resize -1
+  call assert_equal(2, &l:ch)
+  resize +1
+  call assert_equal(1, &l:ch)
+
+  call test_setmouse(&lines - 1, 1)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call test_setmouse(&lines - 2, 1)
+  call feedkeys("\<LeftDrag>", 'xt')
+  call assert_equal(2, &l:ch)
+
+  tabnew | resize +1
+  call assert_equal(1, &l:ch)
+  tabfirst
+  call assert_equal(2, &l:ch)
+
+  tabonly
+  set cmdheight& mouse& laststatus&
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/testdir/test_cmdline.vim

@@ -290,9 +290,10 @@ func Test_changing_cmdheight()
   call term_sendkeys(buf, ":resize -3\<CR>")
   call VerifyScreenDump(buf, 'Test_changing_cmdheight_1', {})
 
-  " using the space available doesn't change the status line
-  call term_sendkeys(buf, ":set cmdheight+=3\<CR>")
+  " :resize now also changes 'cmdheight' accordingly
+  call term_sendkeys(buf, ":set cmdheight+=1\<CR>")
   call VerifyScreenDump(buf, 'Test_changing_cmdheight_2', {})
+  call term_sendkeys(buf, ":set cmdheight-=1\<CR>")
 
   " using more space moves the status line up
   call term_sendkeys(buf, ":set cmdheight+=1\<CR>")
@@ -311,7 +312,7 @@ func Test_changing_cmdheight()
   call term_sendkeys(buf, ":call EchoTwo()\<CR>")
   call VerifyScreenDump(buf, 'Test_changing_cmdheight_6', {})
 
-  " increasing 'cmdheight' doesn't clear the messages that need hit-enter
+  " decreasing 'cmdheight' doesn't clear the messages that need hit-enter
   call term_sendkeys(buf, ":call EchoOne()\<CR>")
   call VerifyScreenDump(buf, 'Test_changing_cmdheight_7', {})
 

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    990,
 /**/
     989,
 /**/