Move out of local cpanm plugin into nil plugin

.github/workflows/default.yml

@@ -11,8 +11,6 @@ jobs:
   build:
     name: Build LaTeXML snap
     runs-on: ubuntu-latest
-    container:
-      image: snapcore/snapcraft:stable
     steps:
       - uses: actions/checkout@v3
 

snap/snapcraft.yaml

@@ -10,11 +10,44 @@ confinement: strict
 
 parts:
   latexml:
-    plugin: cpanm
-    cpanm-packages: ['XML::[email protected]', LaTeXML@$SNAPCRAFT_PROJECT_VERSION]
-    build-packages: [libxml2-dev, libxslt1-dev, libicu-dev, zlib1g-dev]
-    stage-packages: [libxml2, libxslt1.1, zlib1g]
+    plugin: nil
+    source: .
+    override-pull: |
+      apt update
+      apt install -y curl perl build-essential
+      curl -o cpanminus.pl http://cpanmin.us
+      perl -- cpanminus.pl App::cpanminus
+
+    override-build: |
+      apt update
+      apt install -y libxml2-dev libxslt1-dev libicu-dev zlib1g-dev
+
+      # Install cpanm packages
+      cpanm_packages=("XML::[email protected]" "LaTeXML@$SNAPCRAFT_PROJECT_VERSION")
+      for pkg in "${cpanm_packages[@]}"; do
+        cpanm --notest "$pkg"
+      done
+
+      # Modify perl5lib.sh
+      perl_inc=$(perl -e 'print "@INC"')
+      perl_snap_inc=()
+
+      for incpath in $(perl -e 'print "@INC"'); do
+        if [ "$incpath" != "." ]; then
+          perl_snap_inc+=("$SNAP$incpath")
+        fi
+      done
+
+      perl5lib_sh="/usr/bin/perl5lib.sh"
+      echo "env PERL5LIB=$(IFS=:; echo "${perl_snap_inc[*]}") env PATH=$SNAP/usr/local/bin:$PATH \$@" > "$perl5lib_sh"
+      chmod +x "$perl5lib_sh"
+
+      # Copy /usr/local to $SNAP/usr/local
+      cp -r /usr/local/* $SNAP/usr/local/
+
     override-stage: |
+      apt update
+      apt install -y libxml2 libxslt1.1 zlib1g
       snapcraftctl stage
       chmod 0755 ./usr/local/share/sgml
       chmod 0755 ./usr/local/share/sgml/declaration
@@ -27,6 +60,7 @@ parts:
       chmod 0755 ./usr/local/share/xml/entities
       chmod 0755 ./usr/local/share/xml/misc
       chmod 0755 ./usr/local/share/xml/schema
+
 apps:
   latexml:
     environment: