feat(startup): replace bundled site-start.el approach with a custom source patch

Because we bundle libgccjit and gcc libraries, as well as C sources into
the Emacs .app bundle itself, some extra setup is required during
startup of emacs to ensure that native compliation works, and C sources
are found when needed.

Previously this was done by adding a custom site-start.el file to the
Emacs.app bundle, which was loaded at startup. This approach had some
issues, namely that when launching emacs with `-Q` or `--no-site-file`,
the file was not loaded, preventing native compilation from working.

Here we replace the site-start.el approach with a custom patch adding
macos-startup.el, which adds a hook to `after-pdump-load-hook`. This
ensures that the startup code is always run, and before any user
configuration is loaded.

Author: jimeh

build-emacs-for-macos

@@ -19,6 +19,102 @@ require 'yaml'
 
 require 'macho'
 
+# Custom patch for startup of macOS, allowing Emacs .app bundles to correctly
+# use bundled libgccjit libraries and C sources.
+MACOS_STARTUP_PATCH_SOURCE = <<~PATCH
+  From 52b5b168b9db532a18538dc0acc8a1299152fd09 Mon Sep 17 00:00:00 2001
+  From: Jim Myhrberg <[email protected]>
+  Date: Sun, 1 Dec 2024 08:45:51 +0000
+  Subject: [PATCH] feat(macos/startup): add macos-startup.el
+
+  ---
+   lisp/loadup.el        |  1 +
+   lisp/macos-startup.el | 60 +++++++++++++++++++++++++++++++++++++++++++
+   2 files changed, 61 insertions(+)
+   create mode 100644 lisp/macos-startup.el
+
+  diff --git a/lisp/loadup.el b/lisp/loadup.el
+  index bd74a9d6aff..b1d29a3c929 100644
+  --- a/lisp/loadup.el
+  +++ b/lisp/loadup.el
+  @@ -268,6 +268,7 @@
+   (load "minibuffer") ; Needs cl-generic, seq (and define-minor-mode).
+   (load "frame")
+   (load "startup")
+  +(load "macos-startup")
+   (load "term/tty-colors")
+   (load "font-core")
+   (load "emacs-lisp/syntax")
+  diff --git a/lisp/macos-startup.el b/lisp/macos-startup.el
+  new file mode 100644
+  index 00000000000..9fb6887f10b
+  --- /dev/null
+  +++ b/lisp/macos-startup.el
+  @@ -0,0 +1,60 @@
+  +;;; macos-startup.el --- macOS specific startup actions  -*- lexical-binding: t -*-
+  +
+  +;; Maintainer: Jim Myhrberg <[email protected]>
+  +;; Keywords: macos, internal
+  +;; Homepage: https://github.com./jimeh/build-emacs-for-macos
+  +
+  +;; This file is not part of GNU Emacs.
+  +
+  +;;; Commentary:
+  +
+  +;; This file contains macOS specific startup actions for self-contained
+  +;; macOS *.app bundles.  It enables native-compilation via the bundled
+  +;; libgccjit, and for the bundled C-sources to be found for
+  +;; documentation purposes,
+  +
+  +;;; Code:
+  +
+  +(defun macos-startup--in-app-bundle-p ()
+  +  "Check if invoked from a macOS .app bundle."
+  +  (and (eq system-type 'darwin)
+  +       invocation-directory
+  +       (string-match-p "\\.app/Contents/MacOS/?$" invocation-directory)))
+  +
+  +(defun macos-startup--set-source-directory ()
+  +  "Set `source-directory' so that C-sources can be located."
+  +  (let* ((src-dir (expand-file-name "../Resources/src" invocation-directory)))
+  +    (when (file-directory-p src-dir)
+  +      (setq source-directory (file-name-directory src-dir)))))
+  +
+  +(defun macos-startup--setup-library-path ()
+  +  "Configure LIBRARY_PATH env var for native compilation on macOS.
+  +
+  +Ensures LIBRARY_PATH includes paths to the libgccjit and gcc libraries
+  +which are bundled into the .app bundle.  This allows native compilation
+  +to work without any external system dependencies aside from Xcode."
+  +  (let* ((new-paths
+  +          (list (expand-file-name "../Frameworks/gcc/lib" invocation-directory)
+  +                (expand-file-name "../Frameworks/gcc/lib/apple-darwin" invocation-directory)
+  +                "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib"))
+  +         (valid-paths (delq nil (mapcar (lambda (path)
+  +                                          (when (file-directory-p path)
+  +                                            path))
+  +                                        new-paths)))
+  +         (existing-paths (split-string (or (getenv "LIBRARY_PATH") "") ":" t))
+  +         (unique-paths (delete-dups (append valid-paths existing-paths))))
+  +
+  +    (when unique-paths
+  +      (setenv "LIBRARY_PATH" (mapconcat 'identity unique-paths path-separator)))))
+  +
+  +(defun macos-startup--init ()
+  +  "Perform macOS specific startup operations."
+  +  (when (macos-startup--in-app-bundle-p)
+  +    (macos-startup--set-source-directory)
+  +    (when (and (fboundp 'native-comp-available-p)
+  +               (native-comp-available-p))
+  +      (macos-startup--setup-library-path))))
+  +
+  +(add-hook 'after-pdump-load-hook #'macos-startup--init)
+  +
+  +;;; macos-startup.el ends here
+  --
+  2.47.0
+PATCH
+
 class Error < StandardError
 end
 
@@ -1038,6 +1134,8 @@ class Build
       }
     end
 
+    p << { source: MACOS_STARTUP_PATCH_SOURCE }
+
     p.uniq
   end
 
@@ -1068,6 +1166,20 @@ class Build
       else
         apply_patch({ file: patch_file }, target)
       end
+    elsif patch[:source]
+      patch_dir = "#{target}/macos_patches"
+      run_cmd('mkdir', '-p', patch_dir)
+
+      patch_file = File.join(patch_dir, 'patch-{num}.diff')
+      num = 1
+      while File.exist?(patch_file.gsub('{num}', num.to_s.rjust(3, '0')))
+        num += 1
+      end
+      patch_file = patch_file.gsub('{num}', num.to_s.rjust(3, '0'))
+
+      File.write(patch_file, patch[:source])
+
+      apply_patch({ file: patch_file }, target)
     elsif patch[:replace]
       fatal 'Patch replace input error' unless patch[:replace].size == 3
 
@@ -1198,12 +1310,6 @@ class CLIHelperEmbedder < AbstractEmbedder
 end
 
 class CSourcesEmbedder < AbstractEmbedder
-  PATH_PATCH = <<~ELISP
-    ;; Allow Emacs to find bundled C sources.
-    (setq source-directory
-      (expand-file-name ".." (file-name-directory load-file-name)))
-  ELISP
-
   attr_reader :source_dir
 
   def initialize(app, source_dir)
@@ -1228,15 +1334,6 @@ class CSourcesEmbedder < AbstractEmbedder
         src_dir, target_dir, File.join('**', '*.{awk,c,cc,h,in,m,mk}')
       )
     end
-
-    if File.exist?(site_start_el_file) &&
-       File.read(site_start_el_file).include?(PATH_PATCH)
-      return
-    end
-
-    debug "Patching '#{relative_app_path(site_start_el_file)}' to allow " \
-          'Emacs to find bundled C sources'
-    File.open(site_start_el_file, 'a') { |f| f.puts("\n#{PATH_PATCH}") }
   end
 
   private
@@ -1521,49 +1618,13 @@ class GccLibEmbedder < AbstractEmbedder
 
     FileUtils.rm(Dir[File.join(target_dir, '**', '.DS_Store')], force: true)
 
-    if target_darwin_dir != sanitized_target_darwin_dir
-      run_cmd('mv', target_darwin_dir, sanitized_target_darwin_dir)
-    end
+    return unless target_darwin_dir != sanitized_target_darwin_dir
 
-    env_setup = ERB.new(NATIVE_COMP_ENV_VAR_TPL).result(gcc_info.get_binding)
-    if File.exist?(site_start_el_file) &&
-       File.read(site_start_el_file).include?(env_setup)
-      return
-    end
-
-    debug 'Setting up site-start.el for self-contained native-comp Emacs.app'
-    File.open(site_start_el_file, 'a') { |f| f.puts("\n#{env_setup}") }
+    run_cmd('mv', target_darwin_dir, sanitized_target_darwin_dir)
   end
 
   private
 
-  NATIVE_COMP_ENV_VAR_TPL = <<~ELISP
-    ;; Set LIBRARY_PATH to point at bundled GCC and Xcode Command Line Tools to
-    ;; ensure native-comp works.
-    (when (and (eq system-type 'darwin)
-               (string-match-p "\\.app\\/Contents\\/MacOS\\/?$"
-                               invocation-directory))
-      (let* ((library-path-env (getenv "LIBRARY_PATH"))
-             (devtools-dir
-              "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib")
-             (gcc-dir (expand-file-name
-                       "<%= app_bundle_target_lib_dir %>"
-                       invocation-directory))
-             (darwin-dir (expand-file-name
-                          "<%= app_bundle_target_darwin_lib_dir %>"
-                          invocation-directory))
-             (lib-paths (list)))
-
-        (if library-path-env
-            (push library-path-env lib-paths))
-        (if (file-directory-p devtools-dir)
-            (push devtools-dir lib-paths))
-        (push darwin-dir lib-paths)
-        (push gcc-dir lib-paths)
-
-        (setenv "LIBRARY_PATH" (mapconcat 'identity lib-paths ":"))))
-  ELISP
-
   # Remove all rpaths from Mach-O library files except for @loader_path.
   def tidy_lib_rpaths(directory)
     Dir[File.join(directory, '**', '*.{dylib,so}')].each do |file_path|