Change SupportedOSPlatformAttribute warning

[angelazhangmsft]

Description

Windows projects OS version as SupportedOSPlatformAttribute, and the version number is computed by the minimum OS that supports that contract. When an API isn’t guaranteed to be there, a warning message (see below) points people towards authoring a version check, which is undesirable for WinRT. We should change this warning message to point people towards ApiInformation checks.

Example: If I call this code in a .NET 5 console app with SupportedOSPlatformVersion of 10.0.17763.0:

Console.WriteLine("IsDolbyVisionSupported: " + displayMonitor.IsDolbyVisionSupportedInHdrMode);

The following warning shows:

Severity Code Description Project File Line Source Suppression State Tool
Warning CA1416 This call site is reachable on: 'Windows' 10.0.17763.0 and later. 'DisplayMonitor.IsDolbyVisionSupportedInHdrMode.get' is only supported on: 'Windows' 10.0.19041.0 and later. Net5ConsoleApp C:\Users\angzhang\source\repos\Net5ConsoleApp\Net5ConsoleApp\Program.cs 23 IntelliSense Active Microsoft.CodeAnalysis.NetAnalyzers

Alternative

Alternatively, CsWinRT could remove the projection for this attribute and use the to-be-designed analyzer/attribute for contract checks.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[terrajobst]

@jeffhandley @buyaa-n

[buyaa-n]

@angelazhangmsft how could we know when it should point towards ApiInformation check? Are those APIs (or containing type/assembly) decorated with any distinguishing attribute?

[buyaa-n]

Seems we can use ContractVersionAttribute is that right?

[jeffhandley]

@terrajobst / @angelazhangmsft If I recall correctly on this, we concluded that this change was not necessary; is that correct?