crystal build --cross-compile should generate a helpful target script

[skull-squadron]

Feature Request

Problem statement

• {shards|crystal} build --cross-compile --target ... produces an incomplete solution

Compounding factors

• Creaky, brittle, manual steps should be avoided
• The doc for cross-compilation is also currently out-of-date (missing libevent)

Solution

• It's genericide-able :) by dropping a target-specific script into ./bin

Linux

#!/usr/bin/env bash
set -euo pipefail
warn() { echo >&2 "$@"; }
die() { warn "$@"; exit 1; }
help() {
  die "$(cat<<HELP
Usage: $0 {command} ...

Commands

   install-depends

   link TARGET
HELP
)

"
}

linux::link() {
  set -x
  exec "${CC:-cc}" "$1.o" -o "$1" -lpcre -lrt -lm -lgc -lunwind -levent ${CFLAGS-}
}

_sudo() {
  local SUDO
  if [ $UID = 0 ]; then
    SUDO=
  else
    SUDO=${SUDO:-sudo}
  fi
  set -x
  exec $SUDO "$@"
}

_apt() {
  _sudo env DEBIAN_FRONTEND=noninteractive apt-get "$@"
}


#### Distro-specific code

debian::install-depends() {
  _apt update
  _apt -y --no-install-recommends \
    build-essential libevent-dev libpcre3-dev libgc-dev libunwind-dev
}

debian::link() {
  linux::link "$@"
}

ubuntu::install-depends() {
  debian::install_depends "$@"
}

ubuntu::link() {
  linux_link "$@"
}

# fedora::install-depends() {
#   _sudo dnf install -y ...
# }
#
# fedora::link() {
#   linux::link "$@"
# }
#
# ...

#### Main

# Detect distro ID
REGEX=(
  '/^ID=/!d'
  's/^ID=//'
  's/'\''\(.*\)'\''/\1/'
  's/"\(.*\)"/\1/'
)
if ID=$(IFS=';'; sed "${REGEX[*]}" /etc/os-release 2>/dev/null); then
  :
elif [ -n "$(command -v lsb_release 2>/dev/null)" ]; then
  ID=$(lsb_release -is | tr A-Z a-z)
fi

# Validate distro ID
[ -n "$ID" ] || die 'Error: Unknown Linux distro'

# Validate CLI args and dispatch to distro-specific function
CMD="${1-}"; shift || true
case "$CMD" in
  install-depends) ;;
  link)            [[ -e "${1-}" ]] || help ;;
  *)               help ;;
esac
CMD="${ID}::${CMD}"
command "$CMD" || die "Unsupported Linux distro $ID"
"${CMD}" "$@"

and then macOS, Windows, FreeBSD, {{your_os_here}} ...

Long-term solution

• Vendor static libraries and cross-platform linker (lld?)
  • Problems
    • hosts x targets = N^2
    • Needs continuous builds against libraries' upstream stable
    • Disk space
  • Possible partial solution
    • S3-backed sccache

[straight-shoota]

Could you please describe the problem more specifically? I don't follow what you mean with "incomplete".

Judging from the example solution for linux I might guess that you're missing a method to automatically install library dependencies?
But I'm pretty sure that's way out of scope for the compiler to worry about.

[straight-shoota]

/ping @steakknife Could you add some information?