[makazeu]

Closes #113262.

As discussed in #113262 and the video, we're good to make this helper exposed publicly in OperatingSystem.

cc @bartonjs

---

This pull request refactors platform checks throughout the codebase to consolidate Apple-related OS checks into a single method, OperatingSystem.IsApplePlatform(). It also removes support for watchOS, updating both implementation and tests accordingly. This streamlines platform detection logic, reduces duplication, and clarifies current platform support.

Platform detection refactoring:

• Introduced and made public OperatingSystem.IsApplePlatform(), replacing multiple checks for individual Apple platforms (IsMacOS, IsIOS, IsTvOS, IsMacCatalyst) in both product and test code. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

• Updated comments and documentation to reflect the consolidated Apple platform detection, and removed references to watchOS where appropriate. [1] [2] [3] [4]

watchOS deprecation/removal:

• Removed support for watchOS in platform detection APIs (IsWatchOS now always returns false and is documented as unsupported), in version checks, and in native code. [1] [2] [3] [4]

Test updates:

• Updated and simplified tests to use the new IsApplePlatform() method and removed watchOS from test cases and assertions. [1] [2] [3]

These changes improve maintainability by centralizing Apple platform logic and clarify that watchOS is no longer a supported target.

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[vcsjones]

I assume we are going to need a corresponding pull request from someone for the compatibility analyzer? I don't know if the analyzer will handle this without changes. https://github.com/dotnet/dotnet/blob/4fd6fbb479abbacd43b32fdc0ef6f68414cc028d/src/sdk/src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.NetCore.Analyzers/InteropServices/PlatformCompatibilityAnalyzer.cs

[makazeu]

watchOS will NOT be added to IsApplePlatform since modern .NET doesn't support it, and all previous isWatchOS checks had been removed. #117653

[jkotas]

Revert isWatchOS change

I think it was a fine change - for consistency.

We do not currently build and test for watch OS, but the code for it still there.

[jkotas]

all previous isWatchOS checks had been removed

It looks odd when one place in the same file assumes that watchOS does not exist, but other place treats it as a thing.

[makazeu]

all previous isWatchOS checks had been removed

It looks odd when one place in the same file assumes that watchOS does not exist, but other place treats it as a thing.

Yeah, exactly. That’s why I initially added watchOS.

However, after thinking about @vcsjones 's comment on the compatibility analyzer, I decided to remove watchOS for now.

Let's assume the platform compatibility analyzer supports IsApplePlatform() and checks all five platforms, including watchOS:
Consider an API annotated as supported on the other 4 platforms. Even if the call site is guarded by OperatingSystem.IsApplePlatform(), the analyzer would still report a compatibility issue.

I wanted to avoid this situation. After all, new APIs won't explicitly include [SupportedOSPlatform("watchos")] anymore. @jkotas What do you think?

[makazeu]

I assume we are going to need a corresponding pull request from someone for the compatibility analyzer? I don't know if the analyzer will handle this without changes. https://github.com/dotnet/dotnet/blob/4fd6fbb479abbacd43b32fdc0ef6f68414cc028d/src/sdk/src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.NetCore.Analyzers/InteropServices/PlatformCompatibilityAnalyzer.cs

Sure, I'll follow up on this, thanks!

[jkotas]

Let's assume the platform compatibility analyzer supports IsApplePlatform() and checks all five platforms, including watchOS

I do not think that this has any impact on platform compatibility analyzer user experience.

The platform compatibility analyzer only checks compatibly for platforms specified via <SupportedPlatform> item group. This set is Windows/macOS/Linux by default - https://github.com/dotnet/sdk/blob/main/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.SupportedPlatforms.props . It means that you can be calling APIs that are unsupported on SomeOtherOS and it won't warn by default. You have to opt-in your project into checking compatibility with SomeOtherOS.

[makazeu]

Let's assume the platform compatibility analyzer supports IsApplePlatform() and checks all five platforms, including watchOS

I do not think that this has any impact on platform compatibility analyzer user experience.

The platform compatibility analyzer only checks compatibly for platforms specified via <SupportedPlatform> item group. This set is Windows/macOS/Linux by default - https://github.com/dotnet/sdk/blob/main/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.SupportedPlatforms.props . It means that you can be calling APIs that are unsupported on SomeOtherOS and it won't warn by default. You have to opt-in your project into checking compatibility with SomeOtherOS.

@jkotas Thanks for the clear explanation! I hadn’t realized that the analyzer’s platform checks are scoped by <SupportedPlatform>— I learned something new here.

Given that, how would you prefer to handle watchOS in IsApplePlatform()? Should we keep it excluded for consistency with #117653, or include it for consistency with the remaining watchOS detection code? Including it would effectively reintroduce watchOS checks at the call sites converted to IsApplePlatform(), partially undoing that earlier cleanup.

[jkotas]

how would you prefer to handle watchOS in IsApplePlatform()?

Option 1: Add TARGET_WATCHOS to the ifdef in IsApplePlatform

Option 2: Delete TARGET_WATCHOS ifdef in IsWatchOS() and replace with a comment that says watchOS is no longer supported. Also, delete watchOS references in src\libraries\System.Private.CoreLib\src\System\Runtime\InteropServices\RuntimeInformation.Unix.cs, src\libraries\System.Runtime\tests\System.Runtime.Extensions.Tests\System\OperatingSystemTests.cs, src\native\eventpipe\ep-event-source.c, src\native\libs\System.Native\pal_time.c, src\native\libs\System.Security.Cryptography.Native.Apple\pal_ssl.c.

Pick the one you like better - either one is fine with me.

[makazeu]

Pick the one you like better - either one is fine with me.

I prefer option 2 - to do a deeper cleanup of watchOS.