yarn-deduplicate

Cleans up yarn.lock by removing duplicates.

Builds:

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

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 section for a few examples.

Installation

Install the package globally:

 npm install -g yarn-deduplicate

or

 yarn global add yarn-deduplicate

This package also works wth
npx, so you
don't need to install it. For example, to recreate the most common scenario below with npx, run:

 npx yarn-deduplicate yarn.lock

---

Usage

The most common scenario is to run

 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:

 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
• De-duplicating yarn.lock
• https://github.com/yarnpkg/yarn/issues/3778

Deduplication strategies

--strategy <strategy>

highest will try to use the highest installed version. For example, with the following
yarn.lock:

 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:

 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 <package1> <package2> <packageN>

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 <scope1> <scope2> <scopeN>

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 <package1> <package2> <packageN

--exclude-scopes <scope1> <scope2> <scopeN>

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.

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:

 # 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:

 #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:

 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

 # Old
npm install -g yarn-tools

# New
npm install -g yarn-deduplicate

List duplicates

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

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

Deduplicate yarn.lock

 # 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

 # 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
file.