leo/docs/rfc/003-imports-stabilization.md

Leo RFC 003: Imports Stabilization

Authors

The Aleo Team.

Status

FINAL

Summary

This proposal aims to improve the import management system in Leo programs to make program environment more reproducible, predictable and compatible. To achieve that we suggest few changes to Leo CLI and Manifest:

• add a "dependencies" section to Leo Manifest and add a command to pull those dependencies;
• allow custom names for imports to manually resolve name conflicts;
• add "curve" and "proving system" sections to the Manifest;
• add "include" and "exclude" parameters for "proving system" and "curve";
• add a lock file which would store imported dependencies and their relations;

Motivation

The current design of imports does not provide any guarantees on what's stored in program imports and published with the program to Aleo Package Manager. When a dependency is "added," it is stored inside imports folder, and it is possible to manually edit and/or add packages in this folder.

Also, imports are stored under the package name which makes it impossible to import two different packages with the same name.

Another important detail in the scope of this proposal is that in future Leo programs will have the ability to be run with different proving systems and curves, possibly creating incompatibility between programs written for different proving systems or curves. To make a foundation for these features, imports need to be managed with include/exclude lists for allowed (compatible) proving systems and curves.

Design

Leo Manifest - target section

To lay the foundation for the future of the Leo ecosystem and start integrating information about programs compatibility we suggest adding two new fields to the new [target] section of the Leo Manifest: proving_system and curve.

Currently, the Leo compiler only supports Groth16 for the proving system and Bls12_377 for the curve, they are meant to be default values in Leo Manifest.

[project]
name = "first"
version = "0.1.0"
description = "The first package"
license = "MIT"

[target]
curve = "Bls12_377"
proving_system = "Groth16"

These fields are meant to be used to determine whether imported program is compatible to the original when support for different curves and proving systems is added.

Leo Manifest - dependencies

Dependencies section:

[dependencies]
name = { author = "author", package = "package", version = "version" }

# alternative way of adding dependency record
[dependencies.name]
author = "author"
package = "package"
version = "1.0"

Parameters description

name field sets the name of the dependency in Leo code. That way we allow developer to resolve collisions in import names manually. So, for example, if a developer is adding howard/silly-sudoku package to his program, he might define its in-code name as sudoku and import it with that name:

import sudoku;

package, author and version are package name, package author and version respectively. They are already used as arguments in leo add command, so these fields are already understood by the Leo developers.

Leo CLI

To support updated Manifest new command should be added to Leo CLI.

# pull imports
leo fetch

Imports Restructurization

One of the goals of proposed changes is to allow importing packages with the same name but different authors. This has to be solved not only on the language level but also on the level of storing program imports.

We suggest using set of all 3 possible program identifiers for import folder name: author-package@version. Later it can be extended to include hash for version, but having the inital set already solves name collisions.

So, updated imports would look like:

leo-program
├── Leo.toml
├── README.md
├── imports
│   ├── author1-program@0.1.0
│   │    └── ...
│   ├── author2-program2@1.0.4
│        └── ...
├── inputs
│   └── ...
└── src
    └── main.leo

This change would also affect the way imports are being processed on the ASG level, and we'd need to add an imports map as an argument to the Leo compiler. The Leo Manifest's dependencies sections needs to be parsed and passed as a hashmap to the compiler:

first-program  => author1-program@0.1.0
second-program => author2-program2@1.0.4

Leo.lock

For imports map to be generated and read by the Leo binary and then by the Leo compiler, a lock file needs to be created. Lock file should be generated by the leo fetch command, which will pull the dependencies, process their manifests, and put the required information to the file in the root directory of the program called Leo.lock.

Suggested structure of this file is similar to the Cargo.lock file:

[[package]]
name = "suit-mk2"
version = "0.2.0"
author = "ironman"
import_name = "suit-mk2"

[package.dependencies]
garbage = "ironman-suit@0.1.0"

[[package]]
name = "suit"
version = "0.1.0"
author = "ironman"
import_name = "garbage"

In the example above, you can see that all program dependencies are defined as an array called package. Each of the dependencies contains main information about it, including the import_name field which is the imported package's name in the Leo program. Also, it stores relationships between these dependencies in the field dependencies.

The format described here allows the Leo binary to form an imports map which can be passed to the compiler.

It is important to note that Leo.lock file is created only when a package has dependencies. For programs with no dependencies, a lock file is not required and not created.

Recursive Dependencies

This improvement introduces recursive dependencies. To solve this case preemptively Leo CLI needs to check the dependency tree and throw an error when a recursive dependency is met. We suggest implementing simple dependency tree checking while fetching imports - if imported dependency is met on a higher level - abort the execution.

Later this solution can be improved by building a lock file containing all the information on program dependencies, and the file itself will have enough data to track and prevent recursion.

Drawbacks

This change might require the update of already published programs on Aleo PM due to Leo Manifest change. However it is possible to implement it in a backward-compatible way.

It also introduces the danger of having recursive dependencies, this problem is addressed in the Design section above.

Effect on Ecosystem

Proposed improvement provides safety inside Leo programs and should not affect ecosystem except for the tools which use Leo directly (such as Aleo Studio).

It is possible that some of the proposed features will open new features on Aleo PM.

Alternatives

Another approach to the stated cases is to keep everything as we have now but change the way programs are imported and stored and make names unique. Also, current implementation provides some guarantees on import stablitity and consistency.