vim-patch:8.2.4813: pasting text while indent folding may mess up folds

Problem:    Pasting text while indent folding may mess up folds.
Solution:   Adjust the way folds are split. (Brandon Simmons, closes vim/vim#10254)
2c40707baa

src/nvim/fold.c

@@ -1058,7 +1058,7 @@ void cloneFoldGrowArray(garray_T *from, garray_T *to)
 
 // foldFind() {{{2
 /// Search for line "lnum" in folds of growarray "gap".
-/// Set *fpp to the fold struct for the fold that contains "lnum" or
+/// Set "*fpp" to the fold struct for the fold that contains "lnum" or
 /// the first fold below it (careful: it can be beyond the end of the array!).
 ///
 /// @return  false when there is no fold that contains "lnum".
@@ -2615,7 +2615,8 @@ static void foldSplit(buf_T *buf, garray_T *const gap, const int i, const linenr
   // any between top and bot, they have been removed by the caller.
   garray_T *const gap1 = &fp->fd_nested;
   garray_T *const gap2 = &fp[1].fd_nested;
-  if (foldFind(gap1, bot + 1 - fp->fd_top, &fp2)) {
+  (void)foldFind(gap1, bot + 1 - fp->fd_top, &fp2);
+  if (fp2 != NULL) {
     const int len = (int)((fold_T *)gap1->ga_data + gap1->ga_len - fp2);
     if (len > 0) {
       ga_grow(gap2, len);

src/nvim/testdir/test_fold.vim

@@ -881,4 +881,24 @@ func Test_fold_relative_move()
   set fdm& sw& wrap& tw&
 endfunc
 
+" Make sure a fold containing a nested fold is split correctly when using
+" foldmethod=indent
+func Test_fold_split()
+  new
+  let lines =<< trim END
+    line 1
+      line 2
+      line 3
+        line 4
+        line 5
+  END
+  call setline(1, lines)
+  setlocal sw=2
+  setlocal foldmethod=indent foldenable
+  call assert_equal([0, 1, 1, 2, 2], range(1, 5)->map('foldlevel(v:val)'))
+  call append(2, 'line 2.5')
+  call assert_equal([0, 1, 0, 1, 2, 2], range(1, 6)->map('foldlevel(v:val)'))
+  bw!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab