vim-patch:9.1.0294: Text height function does not respect it's argument

Problem:  plines_m_win() does not take into account it's "limit_winheight"
          argument for filler lines below the last line of the buffer.
          (after v9.1.0280)
Solution: Check window height when "limit_winheight" is TRUE.
          (Luuk van Baal)

08b0f632c1

src/nvim/move.c

@@ -2464,7 +2464,7 @@ int pagescroll(Direction dir, int count, bool half)
     if (dir == FORWARD) {
       int n = plines_correct_topline(curwin, curwin->w_topline, NULL, false, NULL);
       if (n - count < curwin->w_height_inner && curwin->w_topline < buflen) {
-        n += plines_m_win(curwin, curwin->w_topline + 1, buflen, true);
+        n += plines_m_win(curwin, curwin->w_topline + 1, buflen, false);
       }
       if (n - count < curwin->w_height_inner) {
         count = n - curwin->w_height_inner;

src/nvim/plines.c

@@ -880,14 +880,17 @@ int plines_m_win(win_T *wp, linenr_T first, linenr_T last, bool limit_winheight)
 {
   int count = 0;
 
-  while (first <= last) {
+  while (first <= last && (!limit_winheight || count < wp->w_height_inner)) {
     linenr_T next = first;
-    count += plines_win_full(wp, first, &next, NULL, false, limit_winheight);
+    count += plines_win_full(wp, first, &next, NULL, false, false);
     first = next + 1;
   }
   if (first == wp->w_buffer->b_ml.ml_line_count + 1) {
     count += win_get_fill(wp, first);
   }
+  if (limit_winheight && count > wp->w_height_inner) {
+    return wp->w_height_inner;
+  }
   return count;
 }
 

test/old/testdir/test_diffmode.vim

@@ -1774,17 +1774,19 @@ endfunc
 
 " Ctrl-D reveals filler lines below the last line in the buffer.
 func Test_diff_eob_halfpage()
-  5new
+  new
   call setline(1, ['']->repeat(10) + ['a'])
   diffthis
-  call assert_true(5, winheight(5))
+  new
-  5new
   call setline(1, ['']->repeat(3) + ['a', 'b'])
   diffthis
+  resize 5
   wincmd j
-  resize 7
+  resize 5
-  exe "norm! G\<C-D>"
+  norm G
-  call assert_equal(6, line('w0'))
+  call assert_equal(7, line('w0'))
+  exe "norm! \<C-D>"
+  call assert_equal(8, line('w0'))
 
   %bwipe!
 endfunc