patch 9.1.0208: winfixbuf does not allow to re-edit current buffer

Problem:  winfixbuf does not allow to re-edit current buffer
          (Tim Pope, after v9.1.0147)
Solution: Explicitly allow :e even when 'winfixbuf' is set,
          since it just re-loads the current buffer
          (Colin Kennedy)

fixes: #14237
closes: #14286

Signed-off-by: Colin Kennedy <colinvfx@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/ex_docmd.c

@@ -460,6 +460,40 @@ restore_dbg_stuff(struct dbg_stuff *dsp)
 }
 #endif
 
+/*
+ * Check if ffname differs from fnum.
+ * fnum is a buffer number. 0 == current buffer, 1-or-more must be a valid buffer ID.
+ * ffname is a full path to where a buffer lives on-disk or would live on-disk.
+ *
+ */
+    static int
+is_other_file(int fnum, char_u *ffname)
+{
+  if (fnum != 0)
+  {
+    if (fnum == curbuf->b_fnum)
+      return FALSE;
+
+    return TRUE;
+  }
+
+  if (ffname == NULL)
+    return TRUE;
+
+  if (*ffname == NUL)
+    return FALSE;
+
+  // TODO: Need a reliable way to know whether a buffer is meant to live on-disk
+  // !curbuf->b_dev_valid is not always available (example: missing on Windows)
+  if (curbuf->b_sfname != NULL
+      && *curbuf->b_sfname != NUL)
+    // This occurs with unsaved buffers. In which case `ffname`
+    // actually corresponds to curbuf->b_sfname
+    return fnamecmp(ffname, curbuf->b_sfname) != 0;
+
+  return otherfile(ffname);
+}
+
 /*
  * do_exmode(): Repeatedly get commands for the "Ex" mode, until the ":vi"
  * command is given.
@@ -7256,12 +7290,15 @@ ex_open(exarg_T *eap)
     static void
 ex_edit(exarg_T *eap)
 {
+    char_u *ffname = eap->cmdidx == CMD_enew ? NULL : eap->arg;
+
     // Exclude commands which keep the window's current buffer
     if (
 	    eap->cmdidx != CMD_badd
 	    && eap->cmdidx != CMD_balt
 	    // All other commands must obey 'winfixbuf' / ! rules
-	    && !check_can_set_curbuf_forceit(eap->forceit))
+	    && (is_other_file(0, ffname) && !check_can_set_curbuf_forceit(eap->forceit))
+    )
         return;
 
     do_exedit(eap, NULL);

src/testdir/test_winfixbuf.vim

@@ -1125,6 +1125,146 @@ func Test_edit()
   call assert_equal(l:other, bufnr())
 endfunc
 
+" Fail :e when selecting a buffer from a relative path if in a different folder
+"
+" In this tests there's 2 buffers
+"
+" foo - lives on disk, in some folder. e.g. /tmp/foo
+" foo - an in-memory buffer that has not been saved to disk. If saved, it
+"       would live in a different folder, /other/foo.
+"
+" The 'winfixbuf' is looking at the in-memory buffer and trying to switch to
+" the buffer on-disk (and fails, because it's a different buffer)
+func Test_edit_different_buffer_on_disk_and_relative_path_to_disk()
+  call s:reset_all_buffers()
+
+  let l:file_on_disk = tempname()
+  let l:directory_on_disk1 = fnamemodify(l:file_on_disk, ":p:h")
+  let l:name = fnamemodify(l:file_on_disk, ":t")
+  execute "edit " . l:file_on_disk
+  write!
+
+  let l:directory_on_disk2 = l:directory_on_disk1 . "_something_else"
+
+  if !isdirectory(l:directory_on_disk2)
+    call mkdir(l:directory_on_disk2)
+  endif
+
+  execute "cd " . l:directory_on_disk2
+  execute "edit " l:name
+
+  let l:current = bufnr()
+
+  call assert_equal(l:current, bufnr())
+  set winfixbuf
+  call assert_fails("edit " . l:file_on_disk, "E1513:")
+  call assert_equal(l:current, bufnr())
+
+  call delete(l:directory_on_disk1)
+  call delete(l:directory_on_disk2)
+endfunc
+
+" Fail :e when selecting a buffer from a relative path if in a different folder
+"
+" In this tests there's 2 buffers
+"
+" foo - lives on disk, in some folder. e.g. /tmp/foo
+" foo - an in-memory buffer that has not been saved to disk. If saved, it
+"       would live in a different folder, /other/foo.
+"
+" The 'winfixbuf' is looking at the on-disk buffer and trying to switch to
+" the in-memory buffer (and fails, because it's a different buffer)
+func Test_edit_different_buffer_on_disk_and_relative_path_to_memory()
+  call s:reset_all_buffers()
+
+  let l:file_on_disk = tempname()
+  let l:directory_on_disk1 = fnamemodify(l:file_on_disk, ":p:h")
+  let l:name = fnamemodify(l:file_on_disk, ":t")
+  execute "edit " . l:file_on_disk
+  write!
+
+  let l:directory_on_disk2 = l:directory_on_disk1 . "_something_else"
+
+  if !isdirectory(l:directory_on_disk2)
+    call mkdir(l:directory_on_disk2)
+  endif
+
+  execute "cd " . l:directory_on_disk2
+  execute "edit " l:name
+  execute "cd " . l:directory_on_disk1
+  execute "edit " l:file_on_disk
+  execute "cd " . l:directory_on_disk2
+
+  let l:current = bufnr()
+
+  call assert_equal(l:current, bufnr())
+  set winfixbuf
+  call assert_fails("edit " . l:name, "E1513:")
+  call assert_equal(l:current, bufnr())
+
+  call delete(l:directory_on_disk1)
+  call delete(l:directory_on_disk2)
+endfunc
+
+" Fail to call `:e first` if called from a starting, in-memory buffer
+func Test_edit_first_buffer()
+  call s:reset_all_buffers()
+
+  set winfixbuf
+  let l:current = bufnr()
+
+  call assert_fails("edit first", "E1513:")
+  call assert_equal(l:current, bufnr())
+
+  edit! first
+  call assert_equal(l:current, bufnr())
+  edit! somewhere_else
+  call assert_notequal(l:current, bufnr())
+endfunc
+
+" Allow reloading a buffer using :e
+func Test_edit_no_arguments()
+  call s:reset_all_buffers()
+
+  let l:current = bufnr()
+  file some_buffer
+
+  call assert_equal(l:current, bufnr())
+  set winfixbuf
+  edit
+  call assert_equal(l:current, bufnr())
+endfunc
+
+" Allow :e selecting the current buffer
+func Test_edit_same_buffer_in_memory()
+  call s:reset_all_buffers()
+
+  let l:current = bufnr()
+  file same_buffer
+
+  call assert_equal(l:current, bufnr())
+  set winfixbuf
+  edit same_buffer
+  call assert_equal(l:current, bufnr())
+endfunc
+
+" Allow :e selecting the current buffer as a full path
+func Test_edit_same_buffer_on_disk_absolute_path()
+  call s:reset_all_buffers()
+
+  let l:file = tempname()
+  let l:current = bufnr()
+  execute "edit " . l:file
+  write!
+
+  call assert_equal(l:current, bufnr())
+  set winfixbuf
+  execute "edit " l:file
+  call assert_equal(l:current, bufnr())
+
+  call delete(l:file)
+endfunc
+
 " Fail :enew but :enew! is allowed
 func Test_enew()
   call s:reset_all_buffers()

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    208,
 /**/
     207,
 /**/