Current Behavior:

In NPM v7 the preinstall script runs after dependencies are installed, which breaks backwards compatibility with NPM v6.

This may have been on purpose, but I do not see the behavior change listed under breaking changes.
https://blog.npmjs.org/post/626173315965468672/npm-v7-series-beta-release-and-semver-major

Expected Behavior:

The preinstall script should run before dependencies are installed.

• I'm aware that a similar issue ([BUG] npm 7.x executes package.json preinstall script after installing dependencies  #2253) was closed with an explanation of "works as intended". I'm requesting for this behavior of NPM v7 to please be reconsidered.
• This same issue appeared in npm@3 and was treated as a bug and fixed: preinstall execution order in npm@3.x npm#10379
• The ability to hook into NPM before dependencies are installed may not be best practice but is sometimes required. This is the primary reason why I use preinstall scripts.
• If preinstall scripts run after dependencies are installed, they seem identical to postinstall scripts and there is no longer a reason for me to use them.

Steps To Reproduce:

Clone this minimal sample repo which contains 2 packages:

• package1 - This package is designed to fail if installed standalone. It expects the file "temp.txt" to exist that has been generated by a parent package before install.
• package2 - This package installs package1 as a dependency, and has a preinstall script that creates the file "temp.txt".

Run cd package2 && npm install.

With NPM v6, the install succeeds because the preinstall script creates "temp.txt" before package1 is installed.
With NPM v7, the install fails because the preinstall script creates "temp.txt" after package1 is installed.

Environment:

• Ubuntu 18.04
• Node: 15.8.0
• npm: 7.5.3