Annotate config.GetValue() with [NotNullIfNotNull]

[dahlbyk]

This is annoying:

// CS8600: Converting possible null value to non-nullable type.
string foo = config.GetValue("foo", "bar");

Before the fix, the updated tests fail to compile:

ConfigurationBinderTests.cs(357,31): error CS8600: Converting null literal or possible null value to non-nullable type.
ConfigurationBinderTests.cs(358,48): error CS8600: Converting null literal or possible null value to non-nullable type.
ConfigurationBinderTests.cs(368,25): error CS8605: Unboxing a possibly null value.
ConfigurationBinderTests.cs(369,29): error CS8605: Unboxing a possibly null value.
ConfigurationBinderTests.cs(370,29): error CS8605: Unboxing a possibly null value.
ConfigurationBinderTests.cs(372,31): error CS8600: Converting null literal or possible null value to non-nullable type.
ConfigurationBinderTests.cs(373,48): error CS8600: Converting null literal or possible null value to non-nullable type.

The source generator has been updated as well.

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[dahlbyk]

Hmm, tried adding System.Diagnostics.CodeAnalysis to the source generator: Update: Changed to fully-qualified reference instead of using.

runtime/src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Specs/BindingHelperInfo.cs

Lines 34 to 41 in cb978a5

	private readonly SortedSet<string> _namespaces = new()
	{
	"System",
	"System.CodeDom.Compiler",
	"System.Globalization",
	"System.Runtime.CompilerServices",
	"Microsoft.Extensions.Configuration",
	};

But build is failing with:

error CS0436: The type 'NotNullIfNotNullAttribute' in 'src\libraries\System.Private.CoreLib\src\System\Diagnostics\CodeAnalysis\NullableAttributes.cs' conflicts with the imported type 'NotNullIfNotNullAttribute' in 'Microsoft.Extensions.Configuration.Binder, Version=9.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'. Using the type defined in 'src\libraries\System.Private.CoreLib\src\System\Diagnostics\CodeAnalysis\NullableAttributes.cs'. [src\libraries\Microsoft.Extensions.Configuration.Binder\tests\SourceGenerationTests\Microsoft.Extensions.Configura
tion.Binder.SourceGeneration.Tests.csproj::TargetFramework=net462]

[tarekgh]

@dahlbyk thanks for submitting the PR. I converted this to a draft PR as there is more need to be done before we can accept this PR. Adding the attribute to these APIs make sense, there is more need to be done here if we want to proceed with that.

• This is kind of breaking change. you can see the app compatibility failures:

❌.packages\microsoft.dotnet.apicompat.task\9.0.100-preview.4.24215.1\build\Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error : API compatibility errors between 'ref/net9.0/Microsoft.Extensions.Configuration.Binder.dll' (left) and 'lib/net9.0/Microsoft.Extensions.Configuration.Binder.dll' (right):
❌.packages\microsoft.dotnet.apicompat.task\9.0.100-preview.4.24215.1\build\Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error CP0016: Cannot add attribute 'System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("defaultValue")' to 'Microsoft.Extensions.Configuration.ConfigurationBinder.GetValue(Microsoft.Extensions.Configuration.IConfiguration, System.Type, string, object?)'.
❌.packages\microsoft.dotnet.apicompat.task\9.0.100-preview.4.24215.1\build\Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error CP0016: Cannot add attribute 'System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("defaultValue")' to 'Microsoft.Extensions.Configuration.ConfigurationBinder.GetValue<T>(Microsoft.Extensions.Configuration.IConfiguration, string, T)'.

We need to decide if we should go with the breaking change and file a breaking change doc for it. Also, we'll need to suppress the app compatibility failure:

error : API breaking changes found. If those are intentional, the APICompat suppression file can be updated by rebuilding with '/p:ApiCompatGenerateSuppressionFile=true' [D:\a\_work\1\s\src\libraries\Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj]

• The attribute NotNullIfNotNullAttribute is support only on netstandard 2.1 which the configuration binder and source gen libraries support netstandard 2.0 too. maybe you need to reference the source file https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/NullableAttributes.cs#L82 to fill the missing attribute.

CC @stephentoub @ericstj if they have any suggestion or recommendation about his change.

[dahlbyk]

Thanks for the initial feedback! I've conditionally included NullableAttributes.cs and suppressed the compatibility failure for Microsoft.Extensions.Configuration.Binder.dll.

[dahlbyk]

I took a stab at updating the source generator. Haven't figured out the CS0436 error mentioned above, but I did noticed it's specific to TargetFramework=net462.

[ericstj]

I don't think making a nullable API less nullable should be actually breaking. I think the issue flagged by APICompat is just that the reference assembly needs to be updated. Please make sure to update reference source in the ref folder. We also don't have strongly typed rules for nullability attributes - so those are just going to get flagged no matter what. If we agree to the change we can suppress the diagnostic.

[dahlbyk]

It turns out this is redundant, as NullableAttributes.cs is already included in most libraries automatically:

runtime/src/libraries/Directory.Build.targets

Lines 170 to 176 in 1c824d9

	<!-- Adds Nullable annotation attributes to C# non .NETCoreApp builds. -->
	<ItemGroup Condition="'$(Nullable)' != '' and
	'$(Nullable)' != 'disable' and
	'$(MSBuildProjectExtension)' == '.csproj' and
	'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
	<Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\NullableAttributes.cs" Link="System\Diagnostics\CodeAnalysis\NullableAttributes.cs" />
	</ItemGroup>

This explains #101336 (comment):

error CS0436: The type 'NotNullIfNotNullAttribute' in 'src\libraries\System.Private.CoreLib\src\System\Diagnostics\CodeAnalysis\NullableAttributes.cs' conflicts with the imported type 'NotNullIfNotNullAttribute' in 'Microsoft.Extensions.Configuration.Binder, ...'.

Microsoft.Extensions.Configuration.Binder.SourceGeneration.Tests.csproj has its own NullableAttributes.cs that it has ignored, but when actually used it conflicts with internal one in Microsoft.Extensions.Configuration.Binder:

runtime/src/libraries/Microsoft.Extensions.Configuration.Binder/src/Properties/InternalsVisibleTo.cs

Line 7 in 1c824d9

[assembly: InternalsVisibleTo("Microsoft.Extensions.Configuration.Binder.SourceGeneration.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]

There may be a cleaner way, but I was able to work around this by allowing projects to opt out of the import.

[tarekgh]

@dahlbyk We shouldn't enforce the definition of the nullable attribute in the source generator as it could lead to complications and problems. The source generator only needs to verify if the attribute is defined during compilation and utilize it accordingly. If it's not defined, we should refrain from emitting any code that relies on this attribute. Users can choose to define the attribute in their code if they wish to support it, granting them flexibility in its usage.

[dahlbyk]

The source generator only needs to verify if the attribute is defined during compilation and utilize it accordingly.

This seems reasonable but I'm new to SG so not sure what this looks like. Any examples/docs?

[tarekgh]

This seems reasonable but I'm new to SG so not sure what this looks like. Any examples/docs?

You may look at the code

runtime/src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Parser/KnownTypeSymbols.cs

Line 78 in cdfc8f2

Half = compilation.GetBestTypeByMetadataName("System.Half");

as example to see how you can search for a type in the compilation. You may look at the docs Compilation.GetTypesByMetadataName and Compilation.GetTypeByMetadataName too for more info.

You search for NotNullIfNotNullAttribute type then if it is found, utilize it.

[dahlbyk]

1. Updated to only emit [NotNullIfNotNull] if it exists
2. Dropped all the churn from the branch
3. Rebased onto latest main

---

Update: build is fine.

I'm curious if the build is going to reproduce local failures that seem related to #95830:

System.TypeLoadException: Method 'get_Keys' in type 'ImplementerOfIDictionaryClass`2' from assembly 'Microsoft.Extensions.Configuration.Binder.Tests, Version=9.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60' does not have an implementation.

System.TypeLoadException: Method 'get_Keys' in type 'ImplementerOfIDictionaryClass`2' from assembly 'Microsoft.Extensions.Configuration.Binder.SourceGeneration.Tests, Version=9.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60' does not have an implementation.

It does, in fact, have an implementation:

runtime/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.TestClasses.Collections.cs

Line 226 in dad01da

public ICollection<TKey> Keys => _dict.Keys;

I might just need to do a full rebuild?

[dahlbyk]

Restored NoIncludeNullableAttributes and rebased onto main again.

[tarekgh]

Thanks @dahlbyk, I added a minor comments, otherwise LGTM .

[tarekgh]

Thanks @dahlbyk for your help getting this working and completing it.