#!/bin/sh

get_vendor()
{
  local origin="$DPKG_ROOT/etc/dpkg/origins/default"
  local vendor

  if [ -n "$DEB_VENDOR" ]; then
    vendor="$DEB_VENDOR"
  elif [ -e "$origin" ]; then
    vendor=$(sed -ne 's/^Vendor: *\([^ ]\+\) */\1/p' "$origin" | tr A-Z a-z)
  fi

  echo "${vendor:-default}"
}

check_merged_usr_via_aliased_dirs()
{
  local vendor

  vendor=$(get_vendor)

  case "$vendor" in
  debian)
    # In Debian some people have gotten so offended by the following _warning_
    # that they have resorted to bullying and abuse. Life's too short, sorry.
    return
    ;;
  ubuntu)
    # Ubuntu does not seem interested in it.
    return
    ;;
  esac

  for d in /bin /sbin /lib /lib32 /libo32 /libx32 /lib64; do
    linkname="$(readlink $d)"
    if [ "$linkname" = "usr$d" ] || [ "$linkname" = "/usr$d" ]; then
      echo "This system uses merged-usr-via-aliased-dirs, going behind dpkg's" >&3
      echo "back, breaking its core assumptions. This can cause silent file" >&3
      echo "overwrites and disappearances, and its general tools misbehavior." >&3
      echo "See <https://wiki.debian.org/Teams/Dpkg/FAQ#broken-usrmerge>." >&3
      break
    fi
  done
}

check_merged_usr_via_aliased_dirs