patch 8.2.1589: term_start() options for size are overruled by 'termwinsize'

Problem:    Term_start() options for size are overruled by 'termwinsize'.
            (Sergey Vlasov)
Solution:   Set 'termwinsize' to the specified size.
diff --git a/src/testdir/term_util.vim b/src/testdir/term_util.vim
index 17f9752..4a5e649 100644
--- a/src/testdir/term_util.vim
+++ b/src/testdir/term_util.vim
@@ -73,7 +73,8 @@
   set t_Co=256 background=light
   hi Normal ctermfg=NONE ctermbg=NONE
 
-  " Make the window 20 lines high and 75 columns, unless told otherwise.
+  " Make the window 20 lines high and 75 columns, unless told otherwise or
+  " 'termwinsize' is set.
   let rows = get(a:options, 'rows', 20)
   let cols = get(a:options, 'cols', 75)
   let statusoff = get(a:options, 'statusoff', 1)
@@ -86,11 +87,12 @@
 
   let cmd = GetVimCommandCleanTerm() .. reset_u7 .. a:arguments
 
-  let options = {
-	\ 'curwin': 1,
-	\ 'term_rows': rows,
-	\ 'term_cols': cols,
-	\ }
+  let options = #{curwin: 1}
+  if &termwinsize == ''
+    let options.term_rows = rows
+    let options.term_cols = cols
+  endif
+
   " Accept other options whose name starts with 'term_'.
   call extend(options, filter(copy(a:options), 'v:key =~# "^term_"'))
 
diff --git a/src/testdir/test_terminal2.vim b/src/testdir/test_terminal2.vim
index 93ace42..f9f221b 100644
--- a/src/testdir/test_terminal2.vim
+++ b/src/testdir/test_terminal2.vim
@@ -109,6 +109,27 @@
   set termwinsize=
 endfunc
 
+func Test_terminal_termwinsize_overruled()
+  let cmd = GetDummyCmd()
+  set termwinsize=5x43
+  let buf = term_start(cmd, #{term_rows: 7, term_cols: 50})
+  call TermWait(buf)
+  call assert_equal([7, 50], term_getsize(buf))
+  exe "bwipe! " .. buf
+
+  let buf = term_start(cmd, #{term_cols: 50})
+  call TermWait(buf)
+  call assert_equal([5, 50], term_getsize(buf))
+  exe "bwipe! " .. buf
+
+  let buf = term_start(cmd, #{term_rows: 7})
+  call TermWait(buf)
+  call assert_equal([7, 43], term_getsize(buf))
+  exe "bwipe! " .. buf
+
+  set termwinsize=
+endfunc
+
 func Test_terminal_termwinkey()
   " make three tabpages, terminal in the middle
   0tabnew
@@ -397,13 +418,17 @@
   call delete('Xfile')
 endfunc
 
-func Test_terminal_no_job()
+func GetDummyCmd()
   if has('win32')
-    let cmd = 'cmd /c ""'
+    return 'cmd /c ""'
   else
     CheckExecutable false
-    let cmd = 'false'
+    return 'false'
   endif
+endfunc
+
+func Test_terminal_no_job()
+  let cmd = GetDummyCmd()
   let term = term_start(cmd, {'term_finish': 'close'})
   call WaitForAssert({-> assert_equal(v:null, term_getjob(term)) })
 endfunc