bug#44446: 27.1; Emacs starts in wrong directory when launched from mac OS Finder

[Richard Brooksby <rb@ravenbrook.com>]

Launching a build of Emacs 27.1-1 downloaded from
<https://emacsformacosx.com/> from the mac OS Finder starts Emacs in "/"
rather than the user's home directory, as it did in Emacs 26.

There appears to be explicit code for handling this case in main.c (see <https://github.com/emacs-mirror/emacs/blob/emacs-26/src/emacs.c#L1304-L1323>), and that
code has changed between Emacs 26 and 27 (see
<https://github.com/emacs-mirror/emacs/commit/900276502fbb4dcabdabc5d7d24b4bc5645f2cf3>)
so it looks to me (at first glance) like this change is the culprit.

Further evidence:

- StackExchange
  <https://apple.stackexchange.com/questions/399187/how-to-set-default-directory-for-emacs-27-1-app/405575#405575>
- build-emacs <https://github.com/caldwell/build-emacs/issues/98>


In GNU Emacs 27.1 (build 1, x86_64-apple-darwin18.7.0, NS appkit-1671.60 Version 10.14.6 (Build 18G95))
of 2020-08-12 built on builder10-14.porkrind.org
Windowing system distributor 'Apple', version 10.3.1671
System Description:  Mac OS X 10.14.6

Recent messages:
Mark set
Mark saved where search started [2 times]
Mark set
Quit
Mark set
C-x C-g is undefined
Quit [2 times]
Making completion list...
Mark saved where search started
<right-fringe> <mouse-1> is undefined

Configured using:
'configure --with-ns '--enable-locallisppath=/Library/Application
Support/Emacs/${version}/site-lisp:/Library/Application
Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY KQUEUE ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES
THREADS JSON PDUMPER

Important settings:
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8-unix

Major mode: C/*l

Minor modes in effect:
  bug-reference-prog-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t
  abbrev-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny format-spec rfc822 mml
mml-sec epa epg epg-config gnus-util rmail rmail-loaddefs
text-property-search time-date mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils cc-mode cc-fonts cc-guess
cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs ruby-mode
smie eieio-opt speedbar sb-image ezimage dframe find-func thingatpt
help-fns radix-tree vc-git bug-reference texinfo cl-extra help-mode
novice misearch multi-isearch dired-aux solarized-rb-theme todotxt-mode
p4 derived edmacro kmacro cl ps-print ps-print-loaddefs ps-def lpr
diff-mode easy-mmode dired dired-loaddefs compile comint ansi-color ring
server finder-inf package easymenu browse-url url-handlers url-parse
auth-source cl-seq eieio eieio-core cl-macs eieio-loaddefs
password-cache json subr-x map url-vars seq byte-opt gv bytecomp
byte-compile cconv cl-loaddefs cl-lib tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/ns-win ns-win
ucs-normalize mule-util term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads kqueue cocoa ns
multi-tty make-network-process emacs)

Memory information:
((conses 16 231923 8254)
(symbols 48 16774 1)
(strings 32 64106 2048)
(string-bytes 1 1899286)
(vectors 16 22498)
(vector-slots 8 288882 15198)
(floats 8 287 160)
(intervals 56 4255 0)
(buffers 1000 19))