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, 10 insertions, 7 deletions

diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index 4179ae40b8..b278a21d8e 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -912,14 +912,17 @@ Buffer nvim_create_buf(Boolean listed, Boolean scratch, Error *err)
     goto fail;
   }
 
+  // Only strictly needed for scratch, but could just as well be consistent
+  // and do this now. buffer is created NOW, not when it latter first happen
+  // to reach a window or aucmd_prepbuf() ..
+  buf_copy_options(buf, BCO_ENTER | BCO_NOHELP);
+
   if (scratch) {
-    aco_save_T aco;
-    aucmd_prepbuf(&aco, buf);
-    set_option_value("bufhidden", STATIC_CSTR_AS_OPTVAL("hide"), OPT_LOCAL);
-    set_option_value("buftype", STATIC_CSTR_AS_OPTVAL("nofile"), OPT_LOCAL);
-    set_option_value("swapfile", BOOLEAN_OPTVAL(false), OPT_LOCAL);
-    set_option_value("modeline", BOOLEAN_OPTVAL(false), OPT_LOCAL);  // 'nomodeline'
-    aucmd_restbuf(&aco);
+    set_string_option_direct_in_buf(buf, "bufhidden", -1, "hide", OPT_LOCAL, 0);
+    set_string_option_direct_in_buf(buf, "buftype", -1, "nofile", OPT_LOCAL, 0);
+    assert(buf->b_ml.ml_mfp->mf_fd < 0);  // ml_open() should not have opened swapfile already
+    buf->b_p_swf = false;
+    buf->b_p_ml = false;
   }
   return buf->b_fnum;