vim-patch:8.0.1763: :argedit does not reuse an empty unnamed buffer

Problem:    :argedit does not reuse an empty unnamed buffer.
Solution:   Add the BLN_CURBUF flag and fix all the side effects. (Christian Brabandt)

46a53dfc29

src/nvim/buffer.c

@@ -1717,11 +1717,7 @@ buf_T * buflist_new(char_u *ffname, char_u *sfname, linenr_T lnum, int flags)
    * buffer.)
    */
   buf = NULL;
-  if ((flags & BLN_CURBUF)
-      && curbuf != NULL
-      && curbuf->b_ffname == NULL
-      && curbuf->b_nwindows <= 1
-      && (curbuf->b_ml.ml_mfp == NULL || BUFEMPTY())) {
+  if ((flags & BLN_CURBUF) && curbuf_reusable()) {
     buf = curbuf;
     /* It's like this buffer is deleted.  Watch out for autocommands that
      * change curbuf!  If that happens, allocate a new buffer anyway. */
@@ -1864,6 +1860,17 @@ buf_T * buflist_new(char_u *ffname, char_u *sfname, linenr_T lnum, int flags)
   return buf;
 }
 
+/// Return true if the current buffer is empty, unnamed, unmodified and used in
+/// only one window. That means it can be reused.
+bool curbuf_reusable(void)
+{
+  return (curbuf != NULL
+          && curbuf->b_ffname == NULL
+          && curbuf->b_nwindows <= 1
+          && (curbuf->b_ml.ml_mfp == NULL || BUFEMPTY())
+          && !curbufIsChanged());
+}
+
 /*
  * Free the memory for the options of a buffer.
  * If "free_p_ff" is true also free 'fileformat', 'buftype' and

src/nvim/ex_cmds2.c

@@ -1952,14 +1952,17 @@ void ex_next(exarg_T *eap)
 void ex_argedit(exarg_T *eap)
 {
   int i = eap->addr_count ? (int)eap->line2 : curwin->w_arg_idx + 1;
+  // Whether curbuf will be reused, curbuf->b_ffname will be set.
+  bool curbuf_is_reusable = curbuf_reusable();
 
   if (do_arglist(eap->arg, AL_ADD, i) == FAIL) {
     return;
   }
   maketitle();
 
-  if (curwin->w_arg_idx == 0 && (curbuf->b_ml.ml_flags & ML_EMPTY)
-      && curbuf->b_ffname == NULL) {
+  if (curwin->w_arg_idx == 0
+      && (curbuf->b_ml.ml_flags & ML_EMPTY)
+      && (curbuf->b_ffname == NULL || curbuf_is_reusable)) {
     i = 0;
   }
   // Edit the argument.
@@ -2257,7 +2260,8 @@ static int alist_add_list(int count, char_u **files, int after)
     }
     for (int i = 0; i < count; i++) {
       ARGLIST[after + i].ae_fname = files[i];
-      ARGLIST[after + i].ae_fnum = buflist_add(files[i], BLN_LISTED);
+      ARGLIST[after + i].ae_fnum = buflist_add(files[i],
+                                               BLN_LISTED | BLN_CURBUF);
     }
     ALIST(curwin)->al_ga.ga_len += count;
     if (old_argcount > 0 && curwin->w_arg_idx >= after) {

src/nvim/testdir/test_arglist.vim

@@ -329,6 +329,18 @@ func Test_argedit()
   %argd
   bwipe! C
   bwipe! D
+
+  " :argedit reuses the current buffer if it is empty
+  %argd
+  " make sure to use a new buffer number for x when it is loaded
+  bw! x
+  new
+  let a = bufnr('')
+  argedit x
+  call assert_equal(a, bufnr(''))
+  call assert_equal('x', bufname(''))
+  %argd
+  bw! x
 endfunc
 
 " Test for the :argdelete command

src/nvim/testdir/test_command_count.vim

@@ -173,7 +173,6 @@ func Test_command_count_4()
   only!
 
   exe bufnr . 'buf'
-  bnext
   let bufnr = bufnr('%')
   let buffers = []
   .,$-bufdo call add(buffers, bufnr('%'))