Developers get warnings when they misuse [SupportedOSPlatform] or [UnsupportedOSPlatform] attributes

[jeffhandley]

The Platform Compatibility Analyzer consumes [SupportedOSPlatform] and [UnsupportedOSPlatform] attributes to report diagnostics when APIs are referenced that are not supported on the targeted platforms. This analyzer and these attributes were introduced in .NET 5.0.

As our platforms expand in .NET 6.0, these attributes will need to be applied on many more APIs and in more complex scenarios. To ensure the attributes are applied correctly, we need to create new diagnostics for missing or invalid attributes.

Here are some examples of when diagnostics should get raised:

• Unknown or invalid platform names/versions Refering to unknown platform names should result in warnings  #45851 and We should validate the syntax for platform names roslyn-analyzers#4015
• Conflicting attributes -- see the Inconsistent List section of the Advanced Scenarios of Combining Attributes [Platform Compatibility Analyzer] Nested APIs shouldn't be allowed to expand the platform set #43971

[danmoseley]

This should not be P0 I think as we don't "control" that priority level.

[jeffhandley]

Thanks, @danmosemsft. At the time of creating this, @terrajobst and I were using zero-based priorities within Priority:1 issues to indicate that the parent Priority:1 item is unsuccessful without its Priority:0 children. But making this Priority:1 will be cleaner for tracking.

[terrajobst]

Works for me :-)

This should not be P0 I think as we don't "control" that priority level.

My understanding is that you can use that priority but you need to explain to our directors why the product can't ship without them.

[buyaa-n]

Consider warning for misuse of newly added SupportedOSPlatformGuard and UnsupportedOSPlatformGuard attributes

[jeffhandley]

I'm closing this based on the original scope. We can file new issues to further improve this experience if needed.