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https://github.com/scinos/yarn-deduplicate

Deduplication tool for yarn.lock files
https://github.com/scinos/yarn-deduplicate

dedupe duplicated-packages duplicates lock-file yarn yarn-lock

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Deduplication tool for yarn.lock files

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# yarn-deduplicate



Cleans up `yarn.lock` by removing duplicates.



Builds:

[![Node.js CI](https://github.com/scinos/yarn-deduplicate/actions/workflows/node.js.yml/badge.svg)](https://github.com/scinos/yarn-deduplicate/actions/workflows/node.js.yml)



This package only works with Yarn v1. Yarn v2 supports package deduplication

[natively](https://github.com/yarnpkg/berry/pull/1558)!



A duplicate package is when two dependencies are resolved to a different version, even when a single

version matches the range specified in the dependencies. See the

[Deduplication strategies](#deduplication-strategies) section for a few examples.



## Installation



Install the package globally:



```sh

npm install -g yarn-deduplicate

```



or



```sh

yarn global add yarn-deduplicate

```



This package also works wth

[npx](https://medium.com/@maybekatz/introducing-npx-an-npm-package-runner-55f7d4bd282b), so you

don't need to install it. For example, to recreate the most common scenario below with `npx`, run:



```sh

npx yarn-deduplicate yarn.lock

```



---



## Usage



The most common scenario is to run



```sh

yarn-deduplicate yarn.lock

```



This will use the default strategy to remove duplicated packages in `yarn.lock`.



If you do not specify the yarn.lock path, it defaults to `yarn.lock`.



Check all available options with:



```sh

yarn-deduplicate --help

```



---



## Duplicated packages



`yarn.lock` contains a list of all the dependencies required by your project (including transitive

dependencies), and the actual package version installed to satisfy those dependencies.



For the context of this project, a "duplicated package" is a package that appears on multiple nodes

of the dependency tree with overlapping version ranges but resolved to different versions.



For example, imagine that your project directly depends on `lodash` and `babel`, and `babel` depends

on `lodash` as well. Specifically, your project depends on `lodash@^1.0.0` and `babel` depends on

`lodash@^1.1.0`. Because how the resolution algorithm works in Yarn, you might end up with two

different copies of `lodash` (for example, version `1.0.1` and `1.2.0`) in your project, even when

`1.2.0` will suffice to satisfy both requirements for `lodash`. That's a "duplicated package".



It is important to note that we do not consider duplicated packages when the version ranges don't

overlap. For example, if your project depends on `underscore@^1.0.0` and `underscore@^2.0.0`. Your

project will end up with two versions of `underscore`, and `yarn-deduplicate` won't change that.



When using `yarn-deduplicate` remember that **it will change your dependency tree**. There are

certain code paths that now will run with a different set of dependencies. It is highly recommended

that you review each change to `yarn.lock`. If the change is too big, use the flag `--packages` to

deduplicate them gradually.



### Why is this necessary?



Yarn documentation seems to suggest this package shouldn't be necessary. For example, in

https://classic.yarnpkg.com/en/docs/cli/dedupe/, it says



> The dedupe command isn’t necessary. `yarn install` will already dedupe.



This is, however, not exactly true. There are cases where yarn will _not_ deduplicate existing

packages. For example, this scenario:



- Install `libA`. It depends on `libB ^1.1.0`. At this point, the latest version of `libB` is

  `1.1.2`, so it gets installed as a transitive dependency in your repo



- After a few days, install `libC`. It also depends on `libB ^1.1.0`. But this time, the latest

  `libB` version is `1.1.3`.



In the above scenario, you'll end up with `[email protected]` and `[email protected]` in your repo.



Find more examples in:



- [yarn-deduplicate — The Hero We Need](https://medium.com/@bnaya/yarn-deduplicate-the-hero-we-need-f4497a362128)

- [De-duplicating yarn.lock](https://medium.com/@scinos/de-duplicating-yarn-lock-ae30be4aa41a)

- https://github.com/yarnpkg/yarn/issues/3778



### Deduplication strategies



`--strategy `



`highest` will try to use the highest installed version. For example, with the following

`yarn.lock`:



```text

library@^1.1.0:

  version "1.2.0"



library@^1.2.0:

  version "1.2.0"



library@^1.3.0:

  version "1.3.0"

```



It will deduplicate `library@^1.1.0` and `library@^1.2.0` to `1.3.0`



`fewer` will try to minimize the number of installed versions by trying to deduplicate to the

version that satisfies most of the ranges first. For example, with the following `yarn.lock`:



```text

library@*:

  version "2.0.0"



library@>=1.1.0:

  version "3.0.0"



library@^1.2.0:

  version "1.2.0"

```



It will deduplicate `library@*` and `library@>=1.1.0` to `1.2.0`.



Note that this may cause some packages to be **downgraded**. Be sure to check the changelogs between

all versions and understand the consequences of that downgrade. If unsure, don't use this strategy.



It is not recommended to use different strategies for different packages. There is no guarantee that

the strategy will be honored in subsequent runs of `yarn-deduplicate` unless the same set of flags

is specified again.



### Progressive deduplication



`--packages   `



Receives a list of packages to deduplicate. It will ignore any other duplicated package not in the

list. This option is recommended when the number of duplicated packages in `yarn.lock` is too big to

be easily reviewed by a human. This will allow for a more controlled and progressive deduplication

of `yarn.lock`.



`--scopes   `



Receives a list of scopes to deduplicate. It will ignore any other duplicated package not in the

list. This option is recommended when deduplicating a large number of inter-dependent packages from

a single scope, such as @babel. This will allow for a more controlled and progressive deduplication

of `yarn.lock` without specifying each package individually.



### Excluding packages



`--exclude     `



With these commands you can exclude certain packages/scopes from the deduplication process. This is

specially useful if you want to apply a different strategy for a scope, for example.



### Pre-release versions



By default, `yarn-deduplicate` will only match pre-release versions if they share they share the

same `major`, `minor` and `patch` versions (example: `^1.2.3-alpha.1` and `1.2.3-alpha.2` can be

deduplicated, but `^1.2.3` and `1.2.4-alpha.1` can't). This matches the behaviour of

[semver](https://docs.npmjs.com/misc/semver#prerelease-tags).



To change this behaviour you can use the flag `--includePrerelease`. This will treat all pre-release

versionas as if they were normal versions (`^1.2.3` and `1.2.4-alpha.1` can be deduplicated).



### Usage in CI



This tool can be used as part of a CI workflow. Adding the flag `--fail` will force the process to

exit with status 1 if there are duplicated packages. Example:



```sh

# Print the list of duplicated packages and exit with status 1

yarn-deduplicate --list --fail



# Deduplicate yarn.lock and exit with status 1 if changes were required

yarn-deduplicate --fail

```



---



## Migration guide



### From 2.x to 3.x



In this version we have adopted variadic arguments from commander.js. These are the equivalent

commands:



```sh

#Old

yarn-deduplicate --packages libA,libB

yarn-deduplicate --scopes @scopeA,@scopeB

yarn-deduplicate --exclude libA,libB



#New

yarn-deduplicate --packages libA libB

yarn-deduplicate --scopes @scopeA @scopeB

yarn-deduplicate --exclude libA libB

```



A consequence of this change is that if you were using one or more of the affected options (

`--packages`, `--scopes` or `--exclude`) **and** a custom path for `yarn.lock`, you need to use `--`

to "stop" package/scope/exclude parsing:



```sh

yarn-deduplicate --packages libA libB -- path/to/yarn.lock

```



### From 0.x to 1.x



In this version we have renamed the project and refactored the CLI. These are the equivalent

commands:



#### Installation



```sh

# Old

npm install -g yarn-tools



# New

npm install -g yarn-deduplicate

```



#### List duplicates



```sh

# Old

yarn-tools list-duplicates path/to/yarn.lock



# New

yarn-deduplicate --list path/to/yarn.lock

```



### Deduplicate yarn.lock



```sh

# Old

yarn-tools fix-duplicates path/to/yarn.lock > tmp

mv tmp path/to/yarn.lock



# New

yarn-deduplicate path/to/yarn.lock

```



### Limit packages to deduplicate yarn.lock



```sh

# Old

yarn-tools fix-duplicates path/to/yarn.lock package1 package2



# New

yarn-deduplicate --packages package1,package2 path/to/yarn.lock

```



## License



Copyright (c) 2022 Sergio Cinos and others. Apache 2.0 licensed, see [LICENSE.txt](LICENSE.txt)

file.