feat: add preinstallOnly script

[hamirmahal]

No description provided.

[hamirmahal]

What / Why

preinstall doesn't actually run before installation. This pull request adds a preinstallOnly script that should run before installation, although I haven't been able to test it with a package.json that has a preinstallOnly script, and I would like to.

[hamirmahal]

I got the idea to use preinstallOnly from #2660 (comment).

you're not wrong, to be honest a lot of our lifecycle scripts are poorly named and don't run exactly when you expect. that's why there's both a prepublish and a prepublishOnly. we have a lot of technical debt here, but changing the expectations about how lifecycle scripts work is a glacier of a breaking change.

the best we can do right now is clearly document when scripts run and what's available to them

[wraithgar]

This would constitute a breaking change and would have to wait till npm 11

[ljharb]

Why would a new script be a breaking change?

[wraithgar]

Ah my oversight, I thought this was moving an existing script

[hamirmahal]

I was able to test it out locally just now, and it appears to work as intended.

[hamirmahal]

package.json.-.cli.WSL_.Ubuntu.-.Visual.Studio.Code.2023-10-10.16-23-47.mp4

[MattCCC]

Works well on mine.

[nkamenar]

Any word on when this will release? My team is switching to pnpm also and running into exactly this problem where someone accidentally runs npm install and we can't prevent it.

[hamirmahal]

@wraithgar what changes would you like this pull request to have, to consider merging it?

[wraithgar]

This is a great contribution and it seems to fit into a point of the install lifecycle that might not be fully covered yet. Our team is currently reviewing the npm lifecycle hooks as a whole and the best resolutions for it moving forward.

Unfortunately this means we won't be able to accept this new feature knowing it may eventually be affected by a breaking change.

[hamirmahal]

Okay, thanks for the explanation.