bug#49271: 28.0.50: native-comp: Signing macOS self-contained .app bundle fails due to new *.eln location

[Jim Myhrberg <contact@jimeh.me>]

Commit 5dd2d50 seems to have moved the native-lisp folder within self-contained
Emacs.app bundles:

- from: "Contents/Resources/native-lisp"
- to:   "Contents/MacOS/lib/emacs/28.0.50/native-lisp"

Unfortunately, Apple's codesign utility blows up with an error if there is any
folder within "Contents/MacOS" (recursively) which contains two dots within its
name. Here is an example of what the error looks like:

    /Users/runner/work/emacs-builds/emacs-builds/builds/Emacs.2021-06-26.b8f9e58.master.macOS-10-15.x86_64/Emacs.app:
bundle format unrecognized, invalid, or unsuitable
    In subcomponent:
/Users/runner/work/emacs-builds/emacs-builds/builds/Emacs.2021-06-26.b8f9e58.master.macOS-10-15.x86_64/Emacs.app/Contents/MacOS/lib/emacs/28.0.50

The above error is from this GitHub Actions workflow run:
https://github.com/jimeh/emacs-builds/runs/2923284812?check_suite_focus=true

The same issue happens locally for me too.

I have so far not found a way to make codesign not blow up on such folders, so
for now I've had to workaround the issue in my build script with the following
changes:

- https://github.com/jimeh/build-emacs-for-macos/commit/eeca7b798de236a3ffc1ab04b0f7735a37ce5af4
- https://github.com/jimeh/build-emacs-for-macos/commit/23b8236e0a66fb09810e8422bedf02f7192a53e4

In summary, I rename:

- from: Emacs.app/Contents/MacOS/lib/emacs/28.0.50/native-lisp/28.0.50-852ecda2
- to:   Emacs.app/Contents/MacOS/lib/emacs/28-0-50/native-lisp/28-0-50-852ecda2

(Note that I had to rename both "28.0.50" and "28.0.50-852ecda2"
folders, as both
trigger the error from codesign.)

I create a symlink from "Contents/native-lisp" to
"Contents/MacOS/lib/emacs/28-0-50/native-lisp".

And finally I patch Emacs.pdmp (Emacs.app/Contents/MacOS/libexec/Emacs.pdmp),
performing the following raw text replacements:

- "lib/emacs/28.0.50/native-lisp/28.0.50-852ecda2/" -->
"lib/emacs/28-0-50/native-lisp/28-0-50-852ecda2/"
- "../native-lisp/28.0.50-852ecda2/" --> "../native-lisp/28-0-50-852ecda2/"

This yields a seemingly actually working Emacs.app bundle, but it re-compiles
all *.eln files in the bundle into the user cache folder. However, there's a
separate bug causing re-compiling which I've reported as bug#49270, so for now I
don't know if my patching would prevent Emacs from dynamically finding existing
*.eln which are not referenced from Emacs.pdmp.

This patching/workaround to get code signing to work feels very hacky and
fragile. It would be great if we could avoid the need for this kind of patch to
be able to codesign the .app bundle.

The way I see it, there's three possible solutions:

- Figure out a way to make Apple's codesign play nice.
- Move the native-lisp folder back to "Contents/Resources/native-lisp", as
  codesign does not complain about folders with two dots in their names within
  the Resources directory.
- Change paths used to store *.eln files within Contents/MacOS so no single
  folder name contains two dots.