NativeAOT: implement better logic for finding the icu data file

[rolfbjarne]

Ref: 6d2e0b5 (#17374)

Once this dotnet/runtime fix reaches us:

https://github.com/dotnet/runtime/pull/87813

We should revert it, and instead set the ICU_DAT_FILE_PATH property in the runtime config to the relative path inside the app bundle.

That would probably be something like:

<ItemGroup>
    <RuntimeHostConfigurationOption Include="ICU_DAT_FILE_PATH" Value="Contents/MonoBundle/icudt.dat" />
</RuntimeHostConfigurationOption>

We could probably do that for all architectures, and remove the current ICU_DAT_FILE_PATH logic in runtime.m

[lemonmojo]

@rolfbjarne @filipnavara

I'm the maintainer of Beyond.NET and am currently looking into fixing this.

Now I am able to get a NativeAOT'd library to correctly locate the icudt.dat in an iOS app bundle.
However, I can't get it to work when running an XCTest bundle. Looking at the fix you mentioned this seems to be implemented using -[NSBundle mainBundle]. So while this works for an app bundle, it unfortunately yields an incorrect path in a XCTest bundle and in turn fails to load the icudt.dat.

let mainPath = Bundle.main.bundlePath
// /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/Library/Xcode/Agents

let testPath = Bundle(for: SomeTypeInTheTestBundle.self).bundlePath
// ~/Library/Developer/Xcode/DerivedData/TestBundle/Build/Products/Variant-ASan/Debug-iphonesimulator/TestBundle.xctest

So while the current fix is good, it's not a silver bullet.
Unfortunately I currently have no good idea for how this can be implemented in a generic way that also supports XCTest bundles.

[ivanpovazan]

Fixed with bf77022