bug#48461: 28.0.50; Renaming a directory in dired doesn't update buffers visiting files within it

[Dale Sedivec]

If you rename a directory via dired, buffers within that directory will
not also have their paths updated with the new directory.

Steps to reproduce:

1. Start "emacs -Q""

2. Evaluate the following:

       (let* ((temp-dir (make-temp-file "dired_bug" t))
              (subdir (expand-file-name "foo" temp-dir))
              (a-file (expand-file-name "zzzz" subdir)))
         (make-directory subdir)
         (find-file a-file)
         (insert "blah blah blah")
         (save-buffer)
         (dired temp-dir))

This should create a temporary directory, a subdirectory "foo" within
that temp dir, it opens a buffer for a file "zzzz" within that
subdirectory "foo", and then a dired buffer on the temp dir.  For
example, you'll now have a buffer on file
"/tmp/dired_bug-123abc/foo/zzzz" and a dired buffer on directory
"/tmp/dired_bug-123abc".

3. In the dired buffer, rename the directory "foo" to "bar"

4. Go back to the buffer on "bar" and look at its path (i.e. eval
buffer-file-name, or C-x C-w and look at the path, or just try to
modify the file and then save it)

Expected result: The buffer that was visiting ".../foo/zzzz" will now
visit ".../bar/zzzz" because ".../foo" was renamed to ".../bar"

Observed result: The buffer visiting ".../foo/zzzz" is still visiting
the old path

I think function `dired-rename-subdir' would actually update the file's
path, but when `dired-rename-file' is called to rename the directory, I
think it never calls `dired-rename-subdir' because of the condition
guarding it (dired-aux.el, end of `dired-rename-file', ca. line 1797):

    ;; See if it's an inserted subdir, and rename that, too.
    (when (file-directory-p file)
      (dired-rename-subdir file newname))

`file' here is the *old* file name, as far as I can tell.  Because the
rename has already been performed, I think `file-directory-p' will
always return nil here.  I suspect changing `file' to `newname' in that
invocation of `file-directory-p' might yield the desired result.

A little work with "git blame" says this condition was added in commit
9e5fd29bede, which says that it "[Fixes a] previous manual mis-merge of
dired-aux".  However, it looks like the lines surrounding this change
were not modified in quite a long time.  I could be misreading, though!


In GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin20.4.0, NS appkit-2022.44 
Version 11.3 (Build 20E232))
of 2021-04-28 built on Dale
Repository revision: e62e87d51651d8dba9e6e612004e689c23428f99
Repository branch: master
System Description:  macOS 11.3

Configured using:
'configure --without-x --with-modules --with-threads --with-xwidgets
--with-zlib --with-xml2 --with-json --with-cairo --with-gnutls
--with-xpm --with-jpeg --with-tiff --with-gif --with-png --with-rsvg
--with-native-compilation --with-ns --enable-ns-self-contained
'CFLAGS=-O2 -I/opt/local/include/gcc10' LDFLAGS=-L/opt/local/lib/gcc10'

Configured features:
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PDUMPER PNG RSVG THREADS TOOLKIT_SCROLL_BARS XIM XWIDGETS ZLIB

Important settings:
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Major mode: Lisp Interaction

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Load-path shadows:
None found.

Features:
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Memory information:
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(symbols 48 9937 1)
(strings 32 29808 2866)
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