Nullable annotation for System.IO.Pipelines

[buyaa-n]

Contributes to #40623
cc: @dotnet/nullablefc

[buyaa-n]

@stephentoub @safern build failed for full framework, seems don't have nullable attributes added System\IO\Pipelines\BufferSegmentStack.cs(26,29): error CS0246: The type or namespace name 'NotNullWhenAttribute' could not be found (are you missing a using directive or an assembly reference?) what we should do?

[safern]

build failed for full framework, seems don't have nullable attributes added System\IO\Pipelines\BufferSegmentStack.cs(26,29): error CS0246: The type or namespace name 'NotNullWhenAttribute' could not be found (are you missing a using directive or an assembly reference?) what we should do?

You need to include this file in the src csproj: https://github.com/dotnet/corefx/blob/master/src/Common/src/CoreLib/System/Diagnostics/CodeAnalysis/NullableAttributes.cs

Add it under this ItemGroup

corefx/src/System.IO.Pipelines/src/System.IO.Pipelines.csproj

Lines 42 to 46 in d217998

	<ItemGroup Condition="'$(TargetGroup)'=='netstandard'">
	<Compile Include="System\IO\Pipelines\StreamExtensions.netstandard.cs" />
	<Compile Include="System\IO\Pipelines\ThreadPoolScheduler.netstandard.cs" />
	<Compile Include="System\IO\Pipelines\CancellationTokenExtensions.netstandard.cs" />
	</ItemGroup>

You also need to add a DefineConstants under this property group:

corefx/src/System.IO.Pipelines/src/System.IO.Pipelines.csproj

Lines 2 to 4 in d217998

	<PropertyGroup>
	<Configurations>netcoreapp-Debug;netcoreapp-Release;netcoreapp3.0-Debug;netcoreapp3.0-Release;netstandard-Debug;netstandard-Release</Configurations>
	</PropertyGroup>

  <PropertyGroup>
    <DefineConstants>$(DefineConstants);INTERNAL_NULLABLE_ATTRIBUTES</DefineConstants>
    <Configurations>netcoreapp-Debug;netcoreapp-Release;netcoreapp3.0-Debug;netcoreapp3.0-Release;netstandard-Debug;netstandard-Release</Configurations>
  </PropertyGroup>

We need to include those attributes when the TargetGroup is netstandard. The configurations for this project are:

corefx/src/System.IO.Pipelines/src/Configurations.props

Lines 2 to 11 in d217998

	<PropertyGroup>
	<PackageConfigurations>
	netstandard;
	netcoreapp3.0;
	</PackageConfigurations>
	<BuildConfigurations>
	$(PackageConfigurations);
	netcoreapp;
	</BuildConfigurations>
	</PropertyGroup>

So whenever we build for uap/netfx it will use the netstandard versionless build configuration, which translates to netstandard2.0 that doesn't have those attributes defined.

[buyaa-n]

@safern added the reference, thank you!

[stephentoub]

@davidfowl, is it correct that this is accessing NextSegment but the while above is using Next? It's not clear to me what the difference is.

[buyaa-n]

Seems at least better assert it instead bang.

[davidfowl]

This actually confused me as well 😄 . I think they are the same. I'm not sure why we're using Next for the null check.

[buyaa-n]

@davidfowl do you want to change segment.Next null check with segment.NextSegment with this PR or its fine as is?

[buyaa-n]

I am going to leave it as is and merge this PR, we can revisit later if needed

[buyaa-n]

@stephentoub @safern please re review