vim-patch:9.0.0898: with 'smoothscroll' cursor is one screen line too far down

Problem:    With 'smoothscroll' cursor is one screen line too far down. (Ernie
            Rael)
Solution:   Add a test that currently has the wrong result so that a fix can
            be made. (issue vim/vim#11436)

75ac25b496

Co-authored-by: Bram Moolenaar <Bram@vim.org>

test/functional/legacy/scroll_opt_spec.lua

@@ -520,4 +520,34 @@ describe('smoothscroll', function()
     feed('0')
     screen:expect(s1)
   end)
+
+  -- oldtest: Test_smoothscroll_long_line_showbreak()
+  it("cursor is not one screen line too far down", function()
+    screen:try_resize(40, 6)
+    exec([[
+      " a line that spans four screen lines
+      call setline(1, 'with lots of text in one line '->repeat(6))
+      set smoothscroll scrolloff=0 showbreak=+++\ 
+    ]])
+    local s1 = [[
+      ^with lots of text in one line with lots |
+      +++ of text in one line with lots of tex|
+      +++ t in one line with lots of text in o|
+      +++ ne line with lots of text in one lin|
+      +++ e with lots of text in one line     |
+                                              |
+    ]]
+    screen:expect(s1)
+    feed('<C-E>')
+    screen:expect([[
+      +++ of text in one line with lots of tex|
+      +++ ^t in one line with lots of text in o|
+      +++ ne line with lots of text in one lin|
+      +++ e with lots of text in one line     |
+      ~                                       |
+                                              |
+    ]])
+    feed('0')
+    screen:expect(s1)
+  end)
 end)

test/old/testdir/test_scroll_opt.vim

@@ -325,6 +325,29 @@ func Test_smoothscroll_one_long_line()
   call StopVimInTerminal(buf)
 endfunc
 
+func Test_smoothscroll_long_line_showbreak()
+  CheckScreendump
+
+  let lines =<< trim END
+      vim9script
+      # a line that spans four screen lines
+      setline(1, 'with lots of text in one line '->repeat(6))
+      set smoothscroll scrolloff=0 showbreak=+++\ 
+  END
+  call writefile(lines, 'XSmoothLongShowbreak', 'D')
+  let buf = RunVimInTerminal('-S XSmoothLongShowbreak', #{rows: 6, cols: 40})
+  call VerifyScreenDump(buf, 'Test_smooth_long_showbreak_1', {})
+  
+  " FIXME: this currently has the cursor in screen line 2, should be one up.
+  call term_sendkeys(buf, "\<C-E>")
+  call VerifyScreenDump(buf, 'Test_smooth_long_showbreak_2', {})
+
+  call term_sendkeys(buf, "0")
+  call VerifyScreenDump(buf, 'Test_smooth_long_showbreak_1', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 " Test that if the current cursor is on a smooth scrolled line, we correctly
 " reposition it. Also check that we don't miscalculate the values by checking
 " the consistency between wincol() and col('.') as they are calculated