yarn replace

[JonnyBurger]

• Start Date: 2018-08-23
• RFC PR: (leave this empty)
• Yarn Issue: (leave this empty)

Summary

Add new subcommand, yarn replace, which removes one package and adds one package in one go.

Motivation

Often, developers find themselves in situations where they try out one package just to find that the package is not useful for them and they want to try another package instead.

Currently, the workflow for this is to execute yarn remove <old-package> and yarn add <new-package> sequentially. By having to execute two commands, native packages recompilation and other redundant tasks have to be executed twice, resulting in a timewaste.

I believe yarn remove <old-package> && yarn add <new-package> is something that developers do commonly. Having a shorthand for these types of operation would also save time for typing.

Detailed design

I propose a new subcommand called replace <old-package> <new-package>.
For example: yarn replace leftpad left-pad.

The flow for this command is like this:

• Check if is installed, throw error if not
• Check if exists in registry, throw error if not
• Remove and generate a temporary lockfile that should be identical to one that would be generated by yarn remove <old-package>. Don't rebuild native dependencies in this step.
  – Execute preinstall lifecycle if needed.
• Install and transform the temporary lockfile into a new lockfile that should be identical to one that would be generated by yarn remove <old-package> && yarn add <new-package>. Save the lockfile. Execute postinstall lifecycle if needed.

Flags

The supported flags for yarn add and yarn remove are the same, execept yarn add has these flags: --ignore-workspace-root-check, --dev, --peer, --optional, --exact, --tilde.

yarn replace should honor all flags that yarn add honors. If the flag is supported by yarn remove as well, it should also be applied to the package removal section of the process. Otherwise, the flag just gets applied to the package installation process instead.

How We Teach This

yarn replace is a convienience command for advanced users and is not a core feature of yarn.
I see this feature in a similar category as yarn upgrade-interactive, a command that is not essential, but is nice to have.

As this command is optional to use for developers, it is not necessary to teach novice users this command. However, advanced users who would like to get efficient when using Yarn, can read up on this command in the documentation

Drawbacks

• It increases the amount of complexity of the Yarn project
• It increases how much code needs to be maintained
• Future additions to yarn add / yarn remove API might not make sense in a yarn replace context.

Alternatives

N/A

Unresolved questions

Which parts of yarn remove and yarn add are exactly redundant? I can think of:
– Bootup of Yarn
– Writing of Lockfile
– Writing of package.json
– Rebuilding of dependencies.