refactor(change): do API changes to buffer without curbuf switch

Most of the messy things when changing a non-current buffer is
not about the buffer, it is about windows. In particular, it is about
`curwin`.

When editing a non-current buffer which is displayed in some other
window in the current tabpage, one such window will be "borrowed" as the
curwin. But this means if two or more non-current windows displayed the buffers,
one of them will be treated differenty. this is not desirable.

In particular, with nvim_buf_set_text, cursor _column_ position was only
corrected for one single window. Two new tests are added: the test
with just one non-current window passes, but the one with two didn't.

Two corresponding such tests were also added for nvim_buf_set_lines.
This already worked correctly on master, but make sure this is
well-tested for future refactors.

Also, nvim_create_buf no longer invokes autocmds just because you happened
to use `scratch=true`. No option value was changed, therefore OptionSet
must not be fired.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/nvim/indent.c b/src/nvim/indent.c
index fb6228ae2d..c16a94f06c 100644
--- a/src/nvim/indent.c
+++ b/src/nvim/indent.c
@@ -1083,7 +1083,7 @@ void ex_retab(exarg_T *eap)
     redraw_curbuf_later(UPD_NOT_VALID);
   }
   if (first_line != 0) {
-    changed_lines(first_line, 0, last_line + 1, 0L, true);
+    changed_lines(curbuf, first_line, 0, last_line + 1, 0L, true);
   }
 
   curwin->w_p_list = save_list;         // restore 'list'
@@ -1107,7 +1107,7 @@ void ex_retab(exarg_T *eap)
   }
   coladvance(curwin->w_curswant);
 
-  u_clearline();
+  u_clearline(curbuf);
 }
 
 /// Get indent level from 'indentexpr'.