docs(scripts): update npm_package_* environment variables documentation

[MaxBlack-dev]

Description

This PR updates the npm_package_* environment variables documentation to reflect the changes made in npm 7.

Changes

• Listed the specific environment variables that npm still provides in npm 7+
• Added note explaining that most package.json fields are no longer provided as environment variables
• Documented that npm_package_json provides the path to package.json for scripts that need to read other fields

Context

In npm 7, the behavior changed from providing all package.json fields as environment variables to only providing a specific subset. This was documented in RFC 21. The old documentation was misleading as it suggested all fields were still available.

Fixes

Fixes #2452

[owlstronaut]

Are you open to documenting the install-specific envars that aren't currently documented anywhere?

cli/workspaces/arborist/lib/arborist/rebuild.js

Lines 310 to 316 in aa1dd7e

	npm_package_resolved: resolved,
	npm_package_integrity: integrity,
	npm_package_json: resolve(path, 'package.json'),
	npm_package_optional: boolEnv(optional),
	npm_package_dev: boolEnv(dev),
	npm_package_peer: boolEnv(peer),
	npm_package_dev_optional:

Also, i don't think main is actually included. I'm not sure if that was missed last time this was updated or why, but it isn't here and in my local tests I'm not seeing a value.

[MaxBlack-dev]

Thank you for the review! I've updated the documentation based on your feedback:

Changes Made

1. Removed npm_package_main - You're correct, this is not actually provided. I verified this in the source code at node_modules/@npmcli/run-script/lib/package-envs.js which only exports name, version, config, engines, and bin.

2. Added install-specific environment variables - Documented the additional variables that are set during install scripts (preinstall, install, postinstall):

   • npm_package_resolved - The resolved URL for the package
   • npm_package_integrity - The integrity hash for the package
   • npm_package_optional - Set to "true" if the package is optional
   • npm_package_dev - Set to "true" if the package is a dev dependency
   • npm_package_peer - Set to "true" if the package is a peer dependency
   • npm_package_dev_optional - Set to "true" if the package is both dev and optional

These are sourced from workspaces/arborist/lib/arborist/rebuild.js lines 310-316 as you referenced.

The updated documentation now accurately reflects what environment variables are actually available to scripts.

[owlstronaut]

Perfect, thank you!