BuildingSimulation: Swift version 6.2-dev issue with blackHole

[pedronahum]

Hi all,

Currently testing your building simulation example in a recent swift version:

swift --version
Swift version 6.2-dev (LLVM 9f6c3d784782c34, Swift 55189bae8e55169)
Target: x86_64-unknown-linux-gnu

And it seems that the latest dev version of Swift doesnt like the blackHole concept:

swift build
Building for debugging...
/..../Sources/main.swift:205:5: error: main actor-isolated var 'blackHole' can not be mutated from a nonisolated context
200 | }
201 | 
202 | var blackHole: Any?
    |     `- note: mutation of this var is only permitted within the actor
203 | @inline(never)
204 | func dontLetTheCompilerOptimizeThisAway<T>(_ x: T) {
    |      `- note: add '@MainActor' to make global function 'dontLetTheCompilerOptimizeThisAway' part of global actor 'MainActor'
205 |     blackHole = x
    |     `- error: main actor-isolated var 'blackHole' can not be mutated from a nonisolated context
206 | }
207 | 

Adding MainActor indeed fixes the issue:

var blackHole: Any?
@inline(never)
@MainActor
func dontLetTheCompilerOptimizeThisAway<T>(_ x: T) {
    blackHole = x
}

swift run
Building for debugging...
[1/1] Write swift-version--1BA0962812E73E12.txt
Build of product 'hello' complete! (0.11s)
trials: 100
timesteps: 20
average forward only time: 4.501960000000002e-06 seconds
average forward and back (gradient) time: 0.00023504620999999993 seconds