fold.c: more edge-cases when updating (#6207)

When foldUpdateIEMSRecurse() re-uses an existing fold, it misses the
case where the existing fold spans from before startlnum to after
firstlnum, the new fold does not span this range, and there is no
"forced start" of a fold. We add a case for this in.

Ensure that if there was no forced break in folds, we merge folds that
now touch each other.

Include testing for a tricky foldmethod=expr case that has never been a
bug. This case works at the moment because of some effects that are not
obvious when reading the code.
A test for this could be useful to ensure a regression doesn't happen.

vim-patch:8.0.0408

1 files changed, 102 insertions, 16 deletions

diff --git a/src/nvim/testdir/test_fold.vim b/src/nvim/testdir/test_fold.vim
index 976c6b5cd1..46c54e8614 100644
--- a/src/nvim/testdir/test_fold.vim
+++ b/src/nvim/testdir/test_fold.vim
@@ -100,22 +100,6 @@ func! Test_indent_fold2()
     bw!
 endfunc
 
-func Test_folds_marker_in_comment()
-  new
-  call setline(1, ['" foo', 'bar', 'baz'])
-  setl fen fdm=marker
-  setl com=sO:\"\ -,mO:\"\ \ ,eO:\"\",:\" cms=\"%s
-  norm! zf2j
-  setl nofen
-  :1y
-  call assert_equal(['" foo{{{'], getreg(0,1,1))
-  :+2y
-  call assert_equal(['baz"}}}'], getreg(0,1,1))
-
-  set foldmethod&
-  bwipe!
-endfunc
-
 func Test_manual_fold_with_filter()
   if !executable('cat')
     return
@@ -138,6 +122,108 @@ func Test_manual_fold_with_filter()
   endfor
 endfunc
 
+func! Test_indent_fold_with_read()
+  new
+  set foldmethod=indent
+  call setline(1, repeat(["\<Tab>a"], 4))
+  for n in range(1, 4)
+    call assert_equal(1, foldlevel(n))
+  endfor
+
+  call writefile(["a", "", "\<Tab>a"], 'Xfile')
+  foldopen
+  2read Xfile
+  %foldclose
+  call assert_equal(1, foldlevel(1))
+  call assert_equal(2, foldclosedend(1))
+  call assert_equal(0, foldlevel(3))
+  call assert_equal(0, foldlevel(4))
+  call assert_equal(1, foldlevel(5))
+  call assert_equal(7, foldclosedend(5))
+
+  bwipe!
+  set foldmethod&
+  call delete('Xfile')
+endfunc
+
+func Test_combining_folds_indent()
+  new
+  let one = "\<Tab>a"
+  let zero = 'a'
+  call setline(1, [one, one, zero, zero, zero, one, one, one])
+  set foldmethod=indent
+  3,5d
+  %foldclose
+  call assert_equal(5, foldclosedend(1))
+
+  set foldmethod&
+  bwipe!
+endfunc
+
+func Test_combining_folds_marker()
+  new
+  call setline(1, ['{{{', '}}}', '', '', '', '{{{', '', '}}}'])
+  set foldmethod=marker
+  3,5d
+  %foldclose
+  call assert_equal(2, foldclosedend(1))
+
+  set foldmethod&
+  bwipe!
+endfunc
+
+func Test_folds_marker_in_comment()
+  new
+  call setline(1, ['" foo', 'bar', 'baz'])
+  setl fen fdm=marker
+  setl com=sO:\"\ -,mO:\"\ \ ,eO:\"\",:\" cms=\"%s
+  norm! zf2j
+  setl nofen
+  :1y
+  call assert_equal(['" foo{{{'], getreg(0,1,1))
+  :+2y
+  call assert_equal(['baz"}}}'], getreg(0,1,1))
+
+  set foldmethod&
+  bwipe!
+endfunc
+
+func s:TestFoldExpr(lnum)
+  let thisline = getline(a:lnum)
+  if thisline == 'a'
+    return 1
+  elseif thisline == 'b'
+    return 0
+  elseif thisline == 'c'
+    return '<1'
+  elseif thisline == 'd'
+    return '>1'
+  endif
+  return 0
+endfunction
+
+func Test_update_folds_expr_read()
+  new
+  call setline(1, ['a', 'a', 'a', 'a', 'a', 'a'])
+  set foldmethod=expr
+  set foldexpr=s:TestFoldExpr(v:lnum)
+  2
+  foldopen
+  call writefile(['b', 'b', 'a', 'a', 'd', 'a', 'a', 'c'], 'Xfile')
+  read Xfile
+  %foldclose
+  call assert_equal(2, foldclosedend(1))
+  call assert_equal(0, foldlevel(3))
+  call assert_equal(0, foldlevel(4))
+  call assert_equal(6, foldclosedend(5))
+  call assert_equal(10, foldclosedend(7))
+  call assert_equal(14, foldclosedend(11))
+
+  call delete('Xfile')
+  bwipe!
+  set foldmethod& foldexpr&
+endfunc
+
 func! Test_move_folds_around_manual()
   new
   let input = PrepIndent("a") + PrepIndent("b") + PrepIndent("c")