bug#58919: 28.2; dired-copy-file-recursive fails to overwrite directory

[Thierry Volpiatto]

This is a followup of this report on reddit:
https://www.reddit.com/r/emacs/comments/yha104/merging_directories_in_dired_am_i_doing_it_wrong/

When using dired-copy to copy a directory to another directory
containing a directory with the same name overwriting fails.
e.g. copy ~/tmp/test/foo/ to ~/tmp/test1/ fails when test1 contain foo/

The bug is IMHO in copy-directory 3th clause of this cond:

(cond ((not (directory-name-p newname))
       ;; If NEWNAME is not a directory name, create it;
       ;; that is where we will copy the files of DIRECTORY.
       (make-directory newname parents))
      ;; NEWNAME is a directory name.  If COPY-CONTENTS is non-nil,
      ;; create NEWNAME if it is not already a directory;
      ;; otherwise, create NEWNAME/[DIRECTORY-BASENAME].
      ((if copy-contents
           (or parents (not (file-directory-p newname)))
         (setq newname (concat newname
                               (file-name-nondirectory directory))))
       (make-directory (directory-file-name newname) parents))
      (t (setq follow t)))

This change was introduced here:

commit 047f02f00f602b9aef63ae8938e12f3f0ab481eb
Author: Paul Eggert <eggert@cs.ucla.edu>
Date:   Wed Sep 20 11:49:12 2017 -0700

    Fix new copy-directory bug with empty dirs
    
    Problem reported by Afdam Plaice (Bug#28520) and by Eli Zaretskii
    (Bug#28483#34).  This is another bug that I introduced in my
    recent copy-directory changes.
    * lisp/files.el (copy-directory): Work with empty subdirectories, too.
    * test/lisp/files-tests.el (files-tests--copy-directory):
    Test for this bug.

Reverting this change fix the bug.

Using this should also fix the bug (based on my 2012 changes), not sure
though if it fix the bug described in the above commit.

(cond ((not (directory-name-p newname))
       ;; If NEWNAME is not a directory name, create it;
       ;; that is where we will copy the files of DIRECTORY.
       (make-directory newname parents))
      ;; NEWNAME is a directory name.  If COPY-CONTENTS is non-nil,
      ;; create NEWNAME if it is not already a directory;
      ;; otherwise, create NEWNAME/[DIRECTORY-BASENAME].
      ((and copy-contents
            (or parents (not (file-directory-p newname))))
       (make-directory (directory-file-name newname) parents))
      ((not copy-contents)
       (setq newname (concat newname
                             (file-name-nondirectory directory)))
       (and (file-exists-p newname)
            (not (file-directory-p newname))
            (error "Cannot overwrite non-directory %s with a directory"
                   newname))
       (make-directory newname t))
      (t (setq follow t)))

It also make readable the clauses handling copy-contents...



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-- 
Thierry