bug#45455: [nextstep]: Emacs master does not compile on Apple Silicon (arm64)

[Artem Loenko]

DO_CODESIGN=$(patsubst arm-apple-darwin%,yes,arm-apple-darwin20.2.0)

indicating that at least here the architecture was detected as
arm-apple-darwin20.2.0. On master it's aarch64-apple-darwin20.2.0 for
me as well.

I believe that you see `arm-apple-darwin` in the emacs-27 branch because aarch64 support was incorporated only for Emacs master branch and was not backported. There is a commit – https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=5d89a9c2846d32b4726faaf5c8652f3f23dc7d73 with the following changes in the master:

diff --git a/build-aux/config.guess b/build-aux/config.guess
index 92bfc33e29..e94095c5fb 100755
--- a/build-aux/config.guess
+++ b/build-aux/config.guess
@@ -2,7 +2,7 @@
 # Attempt to guess a canonical system name.
 #   Copyright 1992-2020 Free Software Foundation, Inc.
 
-timestamp='2020-04-26'
+timestamp='2020-07-12'
 
 # This file is free software; you can redistribute it and/or modify it
 # under the terms of the GNU General Public License as published by
@@ -1342,6 +1342,9 @@ EOF
     *:Rhapsody:*:*)
  echo "$UNAME_MACHINE"-apple-rhapsody"$UNAME_RELEASE"
  exit ;;
+    arm64:Darwin:*:*)
+ echo aarch64-apple-darwin"$UNAME_RELEASE"
+ exit ;;
     *:Darwin:*:*)
  UNAME_PROCESSOR=`uname -p`
  case $UNAME_PROCESSOR in

But in the `emacs-27` branch it calculates with a simple `uname -r` – to the `arm-apple-darwin` (I was able to reproduce it locally on the `emacs-27` branch).

IIUC the only thing that this line does is to check whether to
codesign the resulting binary. That's necessary on Apple Silicon.
Maybe we should codesign on all macOS installations? It shouldn't hurt
even if it's not needed.

Yes, you are right. The problem has nothing to do with `temacs`; it is about signing. I tried to call `codesign` explicitly, and everything works fine in this case. About codesigning for all macOS installations, I am not sure. Such change can break things in many unexpected ways from my point of view. It is better to stay on the safe side.

I see two options:

- Backport `arm64:Darwin:*:*)` support within `config.guess` to emacs-27 branch and switch to `aarch64-apple-darwin` everywhere

- Do not backport, but switch to `aarch64-apple-darwin` everywhere anyway :)

What do you think?

Regards,

Artem Loenko