Add package magic script

[mkaput]

Add a new “magic” script (magic in that sense that Scarb has some logic that makes use of this script, like the test one being also used by scarb test command) called package. While running scarb package it will look for this script and, if present, it will execute it after preparing the tarball directory and before making an archive. The script will be run with PWD set to tarball preparation directory (unlike package directory, this is important and is exceptional!).

This script will be used to automate prebuilding macros (as an alternative to forcing devs to do this manually, see #1770). The rough procedure should look like this:

1. Create directory target/scarb/cairo-plugin in tarball preparation directory.
2. For each target triplet (see platform support for full list):
   1. call rustup component add $TARGET (avoid doing that if we can cheaply detect if it’s already installed)
   2. call cargo build --target $TARGET to build the plugin (note: ensure cargo shows a clear message if any build tools are missing)
   3. copy generated *.so/*.dll + debug info files to target/scarb/cairo-plugin directory, following this naming pattern:
      ${PACKAGE_NAME}_v${PACKAGE_VERSION}_${TARGET}.${so|dylib|dll}
3. Ensure no other garbage is left in tarball directory. We do not want to publish unwanted files!

Example: usage by Starknet Foundry

Starknet Foundry will use the script mechanism in their CI for automatic packaging. It will implement the packaging procedure as a bash script that will be committed to the repository and hooked as a package script.
We will ask Dojo people to copy Foundry’s approach.
So, Foundry plugin will change its Scarb.toml to look as follows:

[package]
name = "snforge_scarb_plugin"
version = "0.33.1"
edition = "2024_07"

[scripts]
package = "prebuild.sh"

Note

No such task was created in Foundry repo.