[Runtime] load debug env vars from Android system properties

[andrurogerz]

Purpose

Enable setting SWIFT_DEBUG_ vars in Swift Android apps by reading debug.swift.runtime.SWIFT_DEBUG_ system properties during runtime init on Android.

Overview

• Add a private platformInitialize() function to the env var setup in the Swift runtime and implement it only for Android
• Call the new platformInitialize function from each of the swift::runtime::environment::initialize implementations

Background

Because all Android app processes all fork from the same process, they don't pick-up environment changes on launch. Android system properties give us an alternative, standard mechanism to do something similar. Only system properties prefixed with debug. can be set without root permissions.

Validation

Set system properties on an Android device:

adb -d shell setprop debug.org.swift.runtime.SWIFT_DEBUG_ENABLE_METADATA_BACKTRACE_LOGGING 1
adb -d shell setprop debug.org.swift.runtime.SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION 1

Kill and re-launch a simple Android app that initializes the Swift runtime from Application.onCreate.

adb -d shell am force-stop com.example.SwiftAppPackage
adb -d shell am start com.example.SwiftAppPackage/.MainActivity

Using the debugger, confirm these variables are set to true:

swift::runtime::environment::SWIFT_DEBUG_ENABLE_METADATA_BACKTRACE_LOGGING_variable
swift::runtime::environment::SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION _variable

[andrurogerz]

Note to reviewers: this change is primarily useful for swift-inspect Android support, which I have working locally and will publish a PR for as soon as #77938 is merged.

[andrurogerz]

+@compnerd

[andrurogerz]

@compnerd please see my response to your comment and let me know if you have any other suggestions. If you're good with what I have here, please request CI. Thanks!

[compnerd]

I think that we should sink the debug. to the end of the name so that all the Swift properties are co-located (in case we add any additional ones in the future).

[andrurogerz]

@compnerd would you mind triggering test runs on this one?

[compnerd]

@swift-ci please test