Fixes #327
Fixes #328
Fixes electron/forge#3782

Context

The flat function of @electron/osx-sign is used to generate .pkg archives for macOS. These archives can be installed on users' machines in two ways:

• via OS X Installer (i.e. clicking the .pkg archive on your file system)
• via the Mac App Store (MAS)

There are two underlying macOS tools that can be used to generate these archives: productbuild and pkgbuild.

Regression

#282 fixed the problem of not being to use pre/postinstall scripts in .pkg installers by adding an additional pkgbuild incantation to add those scripts and inserting that build into the final productbuild bundle.

It turns out that this created invalid output for MAS build targets. This is because pkgbuild isn't supposed to be used for Mac App Store builds according to the manpage:

A "component package" contains payload to be installed by the OS X Installer. Although a component package can be installed on its own, it is typically incorporated into a product archive, along with a "distribution" and localized resources, using productbuild(1).

To create a product archive for submission to the Mac App Store, do not use pkgbuild. Instead, use productbuild(1) directly.To create a product archive for submission to the Mac App Store, do not use pkgbuild. Instead, use productbuild(1) directly.

Solution

My proposed solution is to branch between the previous and current implementation based on the build target (MAS vs. OS X Installer). This will fix the regression for MAS builds while still preserving the ability to add pre/postinstall scripts for OS X Installer archives.

It turns out that pre/postinstall scripts are a non-feature for MAS builds anyways according to both Apple Developer Technical Support 1 and the productbuild manpage 2.