Background

The Swift Package Manager feature can be turned on by setting the SWIFT_PACKAGE_MANAGER to true.

This environment variable name is a bit generic and might collide with other tooling.

Solution

Add a FLUTTER_ prefix to this environment variable and rename it to FLUTTER_SWIFT_PACKAGE_MANAGER.

However, renaming this would break anyone that's set this environment variable to true. To minimize disruption, I will rename this environment variable in the same release that turns on SwiftPM by default. See: #151567