# Recommended way to migrate an existing package to Pkg3

**URL:** <https://discourse.julialang.org/t/recommended-way-to-migrate-an-existing-package-to-pkg3/11560>\
**Category:** General Usage\
**Created:** [June 9, 2018, 7:26pm UTC](https://discourse.julialang.org/t/recommended-way-to-migrate-an-existing-package-to-pkg3/11560 "2018-06-09T19:26:13Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![dfdx](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dfdx/32/120_2.png) [@dfdx](https://discourse.julialang.org/u/dfdx)\
**Post date:** [June 9, 2018, 7:26pm UTC](https://discourse.julialang.org/t/recommended-way-to-migrate-an-existing-package-to-pkg3/11560/1 "2018-06-09T19:26:13Z")

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I know that Pkg3 is still in active development and detailed documentation is coming soon, but right now I have a couple of issues that block me from updating my packages and thus want to overcome them, either using official tools or recommended workarounds.

1. It seems like in Pkg3 you can’t be `using` another package without `add`ing them to the project. Adding to the project requires `Project.toml`, but there seems to be no official way to generate it for existing package. My current workaround: generate a fake project, copy its `Project.toml` and updated required fields. Is it the recommended to fix the issue? Should I make PRs to METADATA using `Project.toml` generated this way?

2. As far as I understand, dependencies for a package should be both - described in `REQUIRE` and `add`ed to the project using the same versions. Is there easier / less error-prone way to handle deps?

3. `add`ing a project using git URL fails if any of its dependencies cannot be satisfied, so the code isn’t even downloaded to the disk and can’t be modified. My current workaround: `git clone` into `.julia/dev`, but I’m not sure I don’t break any internal machinery using this hack.

Please let me if there are better ways to fix these issues.

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**Author:** ![Nosferican](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nosferican/32/9275_2.png) [@Nosferican](https://discourse.julialang.org/u/Nosferican)\
**Post date:** [June 9, 2018, 8:17pm UTC](https://discourse.julialang.org/t/recommended-way-to-migrate-an-existing-package-to-pkg3/11560/2 "2018-06-09T20:17:06Z")

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1. There should be a default `Project.toml` for your version Julia version. Project specific ones override the default one.
2. When everything is working the dependencies are computed from the `Project.toml` not from `REQUIRE`. You don’t need the `REQUIRE` file anymore.
3. Projects are similar to `.Rproj` and other implementations. You need the whole shebang. You can download them to any directory and work with it there.

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**Author:** ![dfdx](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dfdx/32/120_2.png) [@dfdx](https://discourse.julialang.org/u/dfdx)\
**Post date:** [June 9, 2018, 11:36pm UTC](https://discourse.julialang.org/t/recommended-way-to-migrate-an-existing-package-to-pkg3/11560/3 "2018-06-09T23:36:37Z")

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Thanks for your reply. Unfortunately, your suggestions are relevant only for newly generated or already migrated projects, not the ones that you migrate from Julia 0.6 where there’s just no `Project.toml`.

I’ve found a relevant thread [here](https://discourse.julialang.org/t/problem-with-reassignment-of-uuid-when-a-package-is-registered/11422), especially [this](https://discourse.julialang.org/t/problem-with-reassignment-of-uuid-when-a-package-is-registered/11422/14) and [this](https://discourse.julialang.org/t/problem-with-reassignment-of-uuid-when-a-package-is-registered/11422/15) comments. In particular, they state that one should not create their own `Project.toml` and still add dependencies to REQUIRE for now. But here’s a problem: my package [Espresso.jl](https://github.com/dfdx/Espresso.jl) depends on (now external) `LinearAlgebra` module. I’ve added it to `REQUIRE`, but when testing the package fails with:

> ERROR: The following package names could not be resolved:
> 
> - LinearAlgebra (37e2e46d-f89d-539d-b4ee-838fcccc9c8e in manifest but not in project)  
> Please specify by known `name=uuid`.

If I manually create `Project.toml` and run `add LinearAlgebra`, tests run fine. So either I do something that isn’t recommended at the moment (adding `Project.toml`), or my package gets broken.

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**Author:** ![Nosferican](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nosferican/32/9275_2.png) [@Nosferican](https://discourse.julialang.org/u/Nosferican)\
**Post date:** [June 9, 2018, 11:49pm UTC](https://discourse.julialang.org/t/recommended-way-to-migrate-an-existing-package-to-pkg3/11560/4 "2018-06-09T23:49:04Z")

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All registered packages already have a `Project.toml` which was generated so that these can be handled by the new `stdlib`. You can check those from the registry. For example, for [DataFrames](https://github.com/JuliaRegistries/Uncurated/blob/master/D/DataFrames/Package.toml). You can just copy that file and modify it to include additional metadata (e.g., license, maintainer, project status, etc.). For `stdlib` you can check the UUID from their `project.toml`, (e.g., [LinearAlgebra](https://github.com/JuliaLang/julia/blob/master/stdlib/LinearAlgebra/Project.toml)).

A few comments (right now due to a bug those that depend on `stdlib/Dates` need to wait a bit). There were a few issues that broke Travis for the last couple days (related to upgrading a few libraries in nightly). If you refer to packages for Julia 0.6 that have not been registered yet, you can either first register it and migrate or way a bit longer. There isn’t a “proper” way to register it directly for the moment.

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**Author:** ![dfdx](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dfdx/32/120_2.png) [@dfdx](https://discourse.julialang.org/u/dfdx)\
**Post date:** [June 10, 2018, 12:14am UTC](https://discourse.julialang.org/t/recommended-way-to-migrate-an-existing-package-to-pkg3/11560/5 "2018-06-10T00:14:19Z")

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> [@Nosferican](#):
>
> All registered packages already have a `Project.toml` which was generated so that these can be handled by the new `stdlib` . You can check those from the registry.

Aha! So that was the missing detail - `Project.toml` files are generated in the registry and not present in the project’s own repository yet. I’ll test it out and come back. Thanks for the tip!

Edit. Taking my `Project.toml` from the registry worked just fine!

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**Author:** ![dawbarton](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dawbarton/32/215461_2.png) [@dawbarton](https://discourse.julialang.org/u/dawbarton)\
**Post date:** [June 10, 2018, 1:21pm UTC](https://discourse.julialang.org/t/recommended-way-to-migrate-an-existing-package-to-pkg3/11560/6 "2018-06-10T13:21:54Z")

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You can also just stick with using REQUIRES by using Compat since it appears that all the stdlib modules are also exported from there (that’s one way you can get v0.7 and v0.6 compatibility at the same time).