$(TargetPlatformIdentifier) is not being set correctly for iOS

[bzd3y]

Apple platform

iOS

Framework version

net9.0-*

Affected platform version

VS 2022 17.13.1

Description

I split this from an issue I created earlier: #22235, but I am going to close that because I think I added it in the wrong place and need to report that through the VS Feedback feature. I'm also not sure I am adding this issue in the right place.
 
I have a project configured with the following:

		<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'ios'">13.0</SupportedOSPlatformVersion>
		<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'maccatalyst'">13.1</SupportedOSPlatformVersion>
		<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'android'">23.0</SupportedOSPlatformVersion>

The last line, for Android, works. The MacCatalyst line also appears to work, though I haven't tested it all the way to deploying.

The first line does not work when deploying to an iOS with an OS version below 18.2. The condition is not met and so the SupportedOSPlatformVersion defaults to 18.2.

Adding a Target to the project file to output the value of $(TargetPlatformIdentifier) has some strange behavior.

When doing a solution rebuild it will output a 'MacCatalyst' (this is why I think the above line for MacCatalyst works) and 'Android'. It will not output 'iOS'.

However, if I do a build by running the app on a remote iOS device, it only outputs 'iOS', as expected. But after that the deploy fails due to the device not having the minimum required OS version of 18.2. It looks like mtouch is what outputs the error. The error is long and formatted all on one line, but it contains the following messages:

INFO: ?<App Name>? Requires a Newer Version of iOS (IXUserPresentableErrorDomain error 16 (0x10))
INFO: NSLocalizedRecoverySuggestion = The system version is lower than the minimum OS version specified for bundle at /var/installd/Library/Caches/com.apple.mobile.installd.staging/temp.iePTy3/extracted/Payload/<App>.Maui.app. Have 17.6.1; need 18.2
INFO: The system version is lower than the minimum OS version specified for bundle at /var/installd/Library/Caches/com.apple.mobile.installd.staging/temp.iePTy3/extracted/Payload/<App>.Maui.app. Have 17.6.1; need 18.2 (MIInstallerErrorDomain error 9 (0x09))

The following configurations do work:

<SupportedOSPlatformVersion Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'ios'">13.0</SupportedOSPlatformVersion>
<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'maccatalyst'">13.1</SupportedOSPlatformVersion>
<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'android'">23.0</SupportedOSPlatformVersion>

and

<TargetPlatformIdentifier Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'ios'">$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)'))</TargetPlatformIdentifier>

<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'ios'">13.0</SupportedOSPlatformVersion>
<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'maccatalyst'">13.1</SupportedOSPlatformVersion>
<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'android'">23.0</SupportedOSPlatformVersion>

For some additional information, if the minimum OS version is set in Info.plist to "13.0" then an error (or warning? I don't remember) is output stating that the value conflicts with the value from the project of "18.2", indicating that it isn't getting picked up and is being defaulted to 18.2.

This part might be subjective, but it seems strange to default the minimum OS version to the maximum OS version. I would think the default OS version should be the minimum OS version supported by the framework. To that point, the configuration from the MAUI template sets SupportedOSPlatformVersion to "11.0". It seems like that should be the default for SupportedOSPlatformVersion isn't specified at all.

Steps to Reproduce

Create a MAUI 9.0 project and add the above lines to the project file. Run the project on a device running a version lower than iOS 18.2. It will build, but not deploy.

Did you find any workaround?

Yes, the last two configurations described above.

Build logs

No response

[rolfbjarne]

This is a bit counterintuitive, but the problem is TargetPlatformIdentifier isn't set at this point in the build process - so the question becomes "why is it working for Mac Catalyst and Android?"

I was able to test both Android and Mac Catalyst, and it doesn't work on either platform. This is easy enough to see with a non-sensical values:

<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'maccatalyst'">1.0</SupportedOSPlatformVersion>
<SupportedOSPlatformVersion Condition="'$(TargetPlatformIdentifier)' == 'android'">1.0</c>

and the build succeeds just fine, for both Android and Mac Catalyst.

changing to:

<SupportedOSPlatformVersion Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'maccatalyst'">1.0</SupportedOSPlatformVersion>
<SupportedOSPlatformVersion Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'android'">1.0</SupportedOSPlatformVersion>

raises a build error on both platforms.

I'm not sure why it seems to work for you, but it might just be that the default value kicks in and you don't see any problems with it.

This part might be subjective, but it seems strange to default the minimum OS version to the maximum OS version. I would think the default OS version should be the minimum OS version supported by the framework. To that point, the configuration from the MAUI template sets SupportedOSPlatformVersion to "11.0". It seems like that should be the default for SupportedOSPlatformVersion isn't specified at all.

We've had different opinions on this internally, and there doesn't seem to be an obvious default logic that works across all platforms. In fact it seem to depend on how old the minimum OS version actually is - would you expect the default to be the minimum iOS version if the minimum was something ridiculous, such as iOS 2.0? This isn't entirely hypothetical, apparently this happens when building for Windows, the SDK supports some rather old versions of Windows.

In any case, I just wanted to acknowledge that your point is something we're aware of, and we may end up changing in the future.

[bzd3y]

I see, thanks for the explanation. Now that you mention it, the others not working makes sense because I remember before this that changing the value wasn't getting rid of some warnings to version guard some code that I thought it should. Now I know why. I guess that should have clued me in.

But shouldn't it be set that early in the build process? Otherwise, what use is it? It doesn't have a _ prefix to indicate it is internal. So now my question is why does that exist if it can't be used?

As for the supported versions, I'll just say that the issue might not be that it doesn't support the minimum by default, but that it only supports exactly the last version by default, so a solution that just handled that differently would probably be better (for example, defaulting to last version - 1 or something like that).

[rolfbjarne]

But shouldn't it be set that early in the build process? Otherwise, what use is it?

It's a known issue, and there's a proposal to improve this scenario: dotnet/designs#291 (which also explains the reason why it behaves like it does today).

[bzd3y]

Ah, okay. Thanks. To be clear, I wasn't arguing or anything. Just curious/confused.

[bzd3y]

@rolfbjarne Do you know if there is an issue with me setting $(TargetPlatformIdentifier) myself like I did in my second work around?

[rolfbjarne]

@bzd3y I believe that should work fine.

[bzd3y]

@rolfbjarne Thanks!