vim-patch:8.2.5155: in diff mode windows may get out of sync

Problem:    In diff mode windows may get out of sync. (Gary Johnson)
Solution:   Avoid that the other window scrolls for 'cursorbind'.
https://github.com/vim/vim/commit/a315ce1f326b836167ca8b1037dafd93eb8d4d4e

3 files changed, 165 insertions, 1 deletions

diff --git a/src/nvim/move.c b/src/nvim/move.c
index bd68ad6f97..6d4eb8ef49 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -2271,7 +2271,13 @@ void do_check_cursorbind(void)
         int restart_edit_save = restart_edit;
         restart_edit = true;
         check_cursor();
-        validate_cursor();
+
+        // Avoid a scroll here for the cursor position, 'scrollbind' is
+        // more important.
+        if (!curwin->w_p_scb) {
+          validate_cursor();
+        }
+
         restart_edit = restart_edit_save;
       }
       // Correct cursor for multi-byte character.
diff --git a/src/nvim/testdir/test_diffmode.vim b/src/nvim/testdir/test_diffmode.vim
index 007b7e0f14..e059ecb493 100644
--- a/src/nvim/testdir/test_diffmode.vim
+++ b/src/nvim/testdir/test_diffmode.vim
@@ -1378,4 +1378,73 @@ func Test_diff_foldinvert()
   set scrollbind&
 endfunc
 
+" This was scrolling for 'cursorbind' but 'scrollbind' is more important
+func Test_diff_scroll()
+  CheckScreendump
+
+  let left =<< trim END
+      line 1
+      line 2
+      line 3
+      line 4
+
+      // Common block
+      // one
+      // containing
+      // four lines
+
+      // Common block
+      // two
+      // containing
+      // four lines
+  END
+  call writefile(left, 'Xleft')
+  let right =<< trim END
+      line 1
+      line 2
+      line 3
+      line 4
+
+      Lorem
+      ipsum
+      dolor
+      sit
+      amet,
+      consectetur
+      adipiscing
+      elit.
+      Etiam
+      luctus
+      lectus
+      sodales,
+      dictum
+
+      // Common block
+      // one
+      // containing
+      // four lines
+
+      Vestibulum
+      tincidunt
+      aliquet
+      nulla.
+
+      // Common block
+      // two
+      // containing
+      // four lines
+  END
+  call writefile(right, 'Xright')
+  let buf = RunVimInTerminal('-d Xleft Xright', {'rows': 12})
+  call term_sendkeys(buf, "\<C-W>\<C-W>jjjj")
+  call VerifyScreenDump(buf, 'Test_diff_scroll_1', {})
+  call term_sendkeys(buf, "j")
+  call VerifyScreenDump(buf, 'Test_diff_scroll_2', {})
+
+  call StopVimInTerminal(buf)
+  call delete('Xleft')
+  call delete('Xright')
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/test/functional/ui/diff_spec.lua b/test/functional/ui/diff_spec.lua
index 5d056cd6c3..36dc5addcd 100644
--- a/test/functional/ui/diff_spec.lua
+++ b/test/functional/ui/diff_spec.lua
@@ -6,6 +6,7 @@ local clear = helpers.clear
 local command = helpers.command
 local insert = helpers.insert
 local write_file = helpers.write_file
+local dedent = helpers.dedent
 local exec = helpers.exec
 
 describe('Diff mode screen', function()
@@ -985,6 +986,93 @@ int main(int argc, char **argv)
       ]])
     end)
   end)
+
+  -- oldtest: Test_diff_scroll()
+  -- This was scrolling for 'cursorbind' but 'scrollbind' is more important
+  it('scrolling works correctly vim-patch:8.2.5155', function()
+    screen:try_resize(40, 12)
+    write_file(fname, dedent([[
+      line 1
+      line 2
+      line 3
+      line 4
+
+      // Common block
+      // one
+      // containing
+      // four lines
+
+      // Common block
+      // two
+      // containing
+      // four lines]]), false)
+    write_file(fname_2, dedent([[
+      line 1
+      line 2
+      line 3
+      line 4
+
+      Lorem
+      ipsum
+      dolor
+      sit
+      amet,
+      consectetur
+      adipiscing
+      elit.
+      Etiam
+      luctus
+      lectus
+      sodales,
+      dictum
+
+      // Common block
+      // one
+      // containing
+      // four lines
+
+      Vestibulum
+      tincidunt
+      aliquet
+      nulla.
+
+      // Common block
+      // two
+      // containing
+      // four lines]]), false)
+    reread()
+
+    feed('<C-W><C-W>jjjj')
+    screen:expect([[
+      {1:  }line 1           │{1:  }line 1            |
+      {1:  }line 2           │{1:  }line 2            |
+      {1:  }line 3           │{1:  }line 3            |
+      {1:  }line 4           │{1:  }line 4            |
+      {1:  }                 │{1:  }^                  |
+      {1:  }{2:-----------------}│{1:  }{4:Lorem             }|
+      {1:  }{2:-----------------}│{1:  }{4:ipsum             }|
+      {1:  }{2:-----------------}│{1:  }{4:dolor             }|
+      {1:  }{2:-----------------}│{1:  }{4:sit               }|
+      {1:  }{2:-----------------}│{1:  }{4:amet,             }|
+      {3:<nal-diff-screen-1  }{7:<al-diff-screen-1.2 }|
+      :e                                      |
+    ]])
+    feed('j')
+    screen:expect([[
+      {1:  }line 1           │{1:  }line 1            |
+      {1:  }line 2           │{1:  }line 2            |
+      {1:  }line 3           │{1:  }line 3            |
+      {1:  }line 4           │{1:  }line 4            |
+      {1:  }                 │{1:  }                  |
+      {1:  }{2:-----------------}│{1:  }{4:^Lorem             }|
+      {1:  }{2:-----------------}│{1:  }{4:ipsum             }|
+      {1:  }{2:-----------------}│{1:  }{4:dolor             }|
+      {1:  }{2:-----------------}│{1:  }{4:sit               }|
+      {1:  }{2:-----------------}│{1:  }{4:amet,             }|
+      {3:<nal-diff-screen-1  }{7:<al-diff-screen-1.2 }|
+      :e                                      |
+    ]])
+  end)
 end)
 
 it('win_update redraws lines properly', function()
@@ -1227,6 +1315,7 @@ it('Align the filler lines when changing text in diff mode', function()
   ]]}
 end)
 
+-- oldtest: Test_diff_binary()
 it('diff mode works properly if file contains NUL bytes vim-patch:8.2.3925', function()
   clear()
   local screen = Screen.new(40, 20)