I was looking at whether it was possible to make a helper tool to build AppImages from crates. There is a similar tool for cargo, which might work as inspiration: https://github.com/StratusFearMe21/cargo-appimage

This tool is a cargo custom command. These are simply programs called cargo-something, which, when put on the PATH, are invoked by cargo something. I haven't found much information about this Cargo feature, but I suppose in Alire could be implemented as an automatic alias to alr exec -P -- alr-something, when alr something is invoked and:

• something is not a built-in subcommand;
• and something is not a user-configured alias;
• and alr-something is found on PATH.

Some custom commands could simply use the inherited environment set by alr exec to make their job. More complex tools could depend on the Alire library to read the alire.toml file or for whatever they could need. cargo-appimage seems to depend on the crates cargo-metadata and cargo-toml for that. Extension of the TOML file to include custom metadata could be needed as well (e.g. an icon is needed to make an AppImage). I don't know if this is already possible with alire.toml.

This feature would allow extending the capabilities of Alire without requiring integration with the Alire project itself, providing easy extension of the Alire ecosystem for particular needs and experimentation.

Examples of Cargo custom commands: https://crates.io/keywords/cargo-subcommand

Related issue: #1151