feat: add chroot-ln helper

Dockerfile.alpine

@@ -22,6 +22,7 @@ ENV BUILD_ROOT=$BUILD_ROOT \
 
 ADD --chmod=0755 chroot-apk.sh /usr/local/bin/chroot-apk
 ADD --chmod=0755 chroot-pip.sh /usr/local/bin/chroot-pip
+ADD --chmod=0755 chroot-ln.sh /usr/local/bin/chroot-ln
 ADD --chmod=0755 remove-py-if-pyc-exists.sh /usr/local/bin/remove-py-if-pyc-exists
 RUN set -eu ; \
     python -m pip install -U pip setuptools ; \

chroot-ln.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env sh
+
+if [ "x$CACHE_ROOT" = 'x' ] || [ "x$BUILD_ROOT" = 'x' ]; then
+    >&2 echo "CACHE_ROOT (${CACHE_ROOT:-not-set}) and/or BUILD_ROOT (${BUILD_ROOT:-not-set}) is not set!"
+    exit 1
+fi
+
+set -e
+set -o pipefail
+
+setup () {
+    >&2 echo "Grafting $CACHE_ROOT into $BUILD_ROOT..."
+    tar -C "$CACHE_ROOT" -cpf - . | tar -C "$BUILD_ROOT" -xpf -
+    return $?
+}
+
+fini () {
+    >&2 echo "Removing APK data from $BUILD_ROOT, storing in $CACHE_ROOT"
+    tar -C "$BUILD_ROOT" -cpf - etc/apk bin/ln bin/busybox var/cache/apk usr/share/apk | tar -C "$CACHE_ROOT" -xpf -
+    $_chroot /bin/ln -sf /usr/bin/dash /bin/sh.bak
+    rm -rf $BUILD_ROOT/bin/ln $BUILD_ROOT/bin/busybox $BUILD_ROOT/etc/apk $BUILD_ROOT/var/cache/apk $BUILD_ROOT/usr/share/apk
+    if $_chroot /usr/bin/dash -c '[ ! -x /bin/sh ]'; then
+        >&2 echo '/bin/sh in chroot failed the vibe check, replacing with a symlink to /usr/bin/dash!'
+        mv $BUILD_ROOT/bin/sh.bak $BUILD_ROOT/bin/sh
+    else
+        >&2 echo '/bin/sh passed the vibe check'
+        rm $BUILD_ROOT/bin/sh.bak
+    fi
+    return $?
+}
+
+trap fini EXIT
+setup
+set -x
+ln $@