Description
The Platform Compatibility Analyzer was introduced in .NET 5.0, raising new diagnostics when APIs are referenced that are unsupported on targeted platforms. The analyzer relies on the [SupportedOSPlatform] and [UnsupportedOSPlatform] attributes, which can be applied to assemblies, types, and members. These annotations only provide a mechanism for marking an API as entirely supported/unsupported--there is currently no way to annotate an API as partially or conditionally supported on a platform.
Conditionally-Supported Platform Annotations
With a mechanism for marking an API as being conditionally supported/unsupported on a platform, we could improve annotations for APIs such as MemoryMappedFile.CreateNew(), where calls with a named memory mapped file (that is, a non-null mapName) are supported on Windows operating systems only.
This could involve creating new attributes such as [SupportedOSPlatformIfNull], [SupportedOSPlatformIfNotNull], [UnsupportedOSPlatformIfNull], and [UnsupportedOSPlatformIfNotNull]. Occurrences of conditional platform support should be researched to determine what types of conditions need to be modeled in such attributes.
Platform-Guard Assertion Annotations
The analyzer already recognizes platform guards using the methods on OperatingSystem, such as OperatingSystem.IsWindows and OperatingSystem.IsWindowsVersionAtLeast. However, the analyzer does not recognize other guard methods or even helper methods that assert platform guards. Expanding this support could involve creating new attributes that indicate that an API asserts platform checks the same way the APIs on OperatingSystem do, potentially even conditionally.
One example is in Thread, there is an internal field for IsThreadStartSupported that indicates whether or not the current platform supports calls to Thread.Start, regardless of which platforms are targeted. Annotations could allow this to be modeled for the analyzer to warn if Threat.Start is called without first checking the corresponding IsThreadStartSupported member.
Additionally, it's expected that projects will commonly create helper methods that wrap around the OperatingSystem calls and these are not currently recognized through the flow analysis in the analyzer. Helper methods that perform platform assertion could be annotated to inform the analyzer that invocation or specific return values indicate platform support.
Conditionally-Supported Platform Annotationsremoved from scope- Platform-Guard Assertion Annotations