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@ahmetsait
Last active Sep 30, 2021
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What would you like to do?

Improve Dub: Solve Dependency Hell

Research on Alternative Approaches

From what I could find using my google-fu;

Maven selects whichever version is closest to the head in the dependency tree¹. Users can include a specific dependency version in the main application to override any sub-package version choice.

Gradle has so called rich version constraints² that can be used to make dependency resolution more strict or relaxed. If version range is defined to be "strict" than it will halt building in case of a conflict similar to Dub.

CLR (Common Language Runtime) allows two versions of the same assembly to be loaded³. I suspect it is very similar to how Rust works but I did not dive into further details.

I believe Rust's approach to solving dependency hell is by far the best path forward.

Milestone Overview

  1. Implement a DMD switch for mangling and referencing symbols with an additional prefix
    -mangle-prefix=path/to/common/package:v2
    Relevant work for this milestone will be on mangle-prefix branch of my dmd fork.
    How it works: With this switch the compiler will add "v2" as a prefix while mangling and referencing any symbols that originate from path/to/common/package.

  2. Implement a DMD switch for importing a source directory locally
    -import-local=path/to/dependency/that/use/common;path/to/common/package
    Relevant work for this milestone will be on import-local branch of my dmd fork.
    How it works: With this switch the compiler will import files in path/to/common/package only for sources under path/to/dependency/that/use/common. It acts similar to -I=directory except it only affects certain files to make importing multiple versions of the same package possible without clashing each other.

  3. Implement a Dub switch (and package config) that will make use of DMD's newly implemented features and also mention these new features in the dependency conflict error message.
    --resolve=multi-verison
    Relevant work for this milestone will be on multi-version branch of my dub fork.
    How it works: In the first step Dub will compile common package by passing -mangle-prefix to the compiler. After that it will pass both -mangle-prefix and -import-local when compiling dependency that use common.

  4. I'm not entirely sure what exactly I'll be doing but I have few things in my mind depending on how everything goes:

    • Implementing a Dub feature that allow users to declare the exact semantic version multi-mapping in their project config.
    • Extensive testing to see how these changes affect real world projects and packages.
    • Proper documentation of all the newly implemented DMD & Dub features.
    • Research on how to allow multiple library subconfigurations to co-exist.
    • Continuing any unfinished work from previous milestones if something goes terribly wrong.

I will be maintaining a repository with example dependency hell scenarios and docs on how to test them.

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