emacs: make trivialBuild know its elisp dependencies in another way (#343201)

pkgs/applications/editors/emacs/build-support/emacs-funcs.sh

@@ -20,15 +20,4 @@ addEmacsVars () {
   if [ -n "${addEmacsNativeLoadPath:-}" ]; then
     addToEmacsNativeLoadPath "$1/share/emacs/native-lisp"
   fi
-
-  # Add sub paths to the Emacs load path if it is a directory
-  # containing .el files. This is necessary to build some packages,
-  # e.g., using trivialBuild.
-  for lispDir in \
-      "$1/share/emacs/site-lisp/"* \
-      "$1/share/emacs/site-lisp/elpa/"*; do
-    if [[ -d $lispDir && "$(echo "$lispDir"/*.el)" ]] ; then
-      addToEmacsLoadPath "$lispDir"
-    fi
-  done
 }

pkgs/applications/editors/emacs/build-support/generic.nix

@@ -86,10 +86,14 @@ libBuildHelper.extendMkDerivation' stdenv.mkDerivation (finalAttrs:
     source ${./emacs-funcs.sh}
     addEmacsVars "$out"
 
+    # package-activate-all is used to activate packages.  In other builder
+    # helpers, package-initialize is used for this purpose because
+    # package-activate-all is not available before Emacs 27.
     find $out/share/emacs -type f -name '*.el' -not -name ".dir-locals.el" -print0 \
       | xargs --verbose -0 -I {} -n 1 -P $NIX_BUILD_CORES sh -c \
           "emacs \
              --batch \
+             -f package-activate-all \
              --eval '(setq native-comp-eln-load-path (cdr native-comp-eln-load-path))' \
              --eval '(setq large-file-warning-threshold nil)' \
              --eval '(setq byte-compile-error-on-warn ${if finalAttrs.turnCompilationWarningToError then "t" else "nil"})' \

pkgs/applications/editors/emacs/build-support/trivial.nix

@@ -19,7 +19,7 @@ args:
       foundMakefile=1
     fi
 
-    emacs -L . --batch -f batch-byte-compile *.el
+    emacs -l package -f package-initialize -L . --batch -f batch-byte-compile *.el
 
     runHook postBuild
   '';