Add code to expose the selected version of a requested package #746

	name: Rust 1.12 compile test

	on:
	push:
	pull_request:
	schedule:
	- cron: "35 2 * * *"

	jobs:
	build:
	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v3
	- name: Work around incompatible crates.io
	shell: bash
	# Point cargo at a rewound copy of crates.io that would be understood
	# at 1.10.0. Unfortunately, pointing at a registry like this is only
	# supported from 1.12.0 and beyond.
	run: \|
	set -ex
	# Tell cargo to use a different copy of crates.io.
	mkdir -p .cargo
	cat <<EOF > .cargo/config
	[source.crates-io]
	registry = "file://$(pwd)/../crates-io-rewound"
	EOF
	cat .cargo/config
	# use an old archive of crates.io, reset back to when rand 0.8.0 didn't
	# exist in index.
	cd ..
	git clone https://github.com/rust-lang/crates.io-index-archive.git --single-branch --branch 'snapshot-2018-09-26' crates-io-rewound
	cd crates-io-rewound
	git checkout -b master
	- name: Set default Rust
	run: rustup default 1.12.0
	- name: Run build
	run: cargo build --verbose
	# tests can't be run because they use ONCE which needs a newer compiler
	# - name: Run unit tests
	# run: cargo test --verbose

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