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Add support for null arrays in the blittable array marshaller's pinning optimization. #1063

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merged 3 commits into from
May 4, 2021
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Add support for null arrays in the blittable array marshaller's pinning optimization. #1063

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b125fd7
Add support for null arrays in the blittable array marshaller's pinni…
jkoritzinsky May 3, 2021
77b7325
Add comment block about the behavior.
jkoritzinsky May 3, 2021
0477f25
Use pointer casting instead of Unsafe.NullRef since we are already us…
jkoritzinsky May 3, 2021
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8 changes: 7 additions & 1 deletion DllImportGenerator/DllImportGenerator.IntegrationTests/ArrayTests.cs
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Expand Up @@ -67,10 +67,16 @@ public class ArrayTests
[Fact]
public void IntArrayMarshalledToNativeAsExpected()
{
var array = new [] { 1, 5, 79, 165, 32, 3 };
var array = new[] { 1, 5, 79, 165, 32, 3 };
Assert.Equal(array.Sum(), NativeExportsNE.Arrays.Sum(array, array.Length));
}

[Fact]
public void NullIntArrayMarshalledToNativeAsExpected()
{
Assert.Equal(-1, NativeExportsNE.Arrays.Sum(null, 0));
}

[Fact]
public void ZeroLengthArrayMarshalledAsNonNull()
{
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53 changes: 45 additions & 8 deletions DllImportGenerator/DllImportGenerator/Marshalling/BlittableArrayMarshaller.cs
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Expand Up @@ -56,21 +56,58 @@ public override IEnumerable<StatementSyntax> Generate(TypePositionInfo info, Stu
var (managedIdentifer, nativeIdentifier) = context.GetIdentifiers(info);
if (!info.IsByRef && !info.IsManagedReturnPosition && context.PinningSupported)
{
string byRefIdentifier = $"__byref_{managedIdentifer}";
if (context.CurrentStage == StubCodeContext.Stage.Marshal)
{
// [COMPAT] We use explicit byref calculations here instead of just using a fixed statement
// since a fixed statement converts a zero-length array to a null pointer.
// Many native APIs, such as GDI+, ICU, etc. validate that an array parameter is non-null
// even when the passed in array length is zero. To avoid breaking customers that want to move
// to source-generated interop in subtle ways, we explicitly pass a reference to the 0-th element
// of an array as long as it is non-null, matching the behavior of the built-in interop system
// for single-dimensional zero-based arrays.

// ref <elementType> <byRefIdentifier> = <managedIdentifer> == null ? ref *(<elementType*)0 : ref MemoryMarshal.GetArrayDataReference(<managedIdentifer>);
var nullRef =
PrefixUnaryExpression(SyntaxKind.PointerIndirectionExpression,
CastExpression(
PointerType(GetElementTypeSyntax(info)),
LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(0))));

var getArrayDataReference =
InvocationExpression(
MemberAccessExpression(
SyntaxKind.SimpleMemberAccessExpression,
ParseTypeName(TypeNames.System_Runtime_InteropServices_MemoryMarshal),
IdentifierName("GetArrayDataReference")),
ArgumentList(SingletonSeparatedList(
Argument(IdentifierName(managedIdentifer)))));

yield return LocalDeclarationStatement(
VariableDeclaration(
RefType(GetElementTypeSyntax(info)))
.WithVariables(SingletonSeparatedList(
VariableDeclarator(Identifier(byRefIdentifier))
.WithInitializer(EqualsValueClause(
RefExpression(ParenthesizedExpression(
ConditionalExpression(
BinaryExpression(
SyntaxKind.EqualsExpression,
IdentifierName(managedIdentifer),
LiteralExpression(
SyntaxKind.NullLiteralExpression)),
RefExpression(nullRef),
RefExpression(getArrayDataReference)))))))));
}
if (context.CurrentStage == StubCodeContext.Stage.Pin)
{
// fixed (<nativeType> <nativeIdentifier> = &MemoryMarshal.GetArrayDataReference(<managedIdentifer>))
// fixed (<nativeType> <nativeIdentifier> = &<byrefIdentifier>)
yield return FixedStatement(
VariableDeclaration(AsNativeType(info), SingletonSeparatedList(
VariableDeclarator(nativeIdentifier)
.WithInitializer(EqualsValueClause(
PrefixUnaryExpression(SyntaxKind.AddressOfExpression,
InvocationExpression(
MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression,
ParseTypeName(TypeNames.System_Runtime_InteropServices_MemoryMarshal),
IdentifierName("GetArrayDataReference")),
ArgumentList(
SingletonSeparatedList(Argument(IdentifierName(managedIdentifer)))
))))))),
IdentifierName(byRefIdentifier)))))),
EmptyStatement());
}
yield break;
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2 changes: 1 addition & 1 deletion DllImportGenerator/DllImportGenerator/TypeNames.cs
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Expand Up @@ -44,7 +44,7 @@ public static string MarshalEx(AnalyzerConfigOptions options)
public const string System_Runtime_InteropServices_OutAttribute = "System.Runtime.InteropServices.OutAttribute";

public const string System_Runtime_InteropServices_InAttribute = "System.Runtime.InteropServices.InAttribute";

public const string System_Runtime_CompilerServices_SkipLocalsInitAttribute = "System.Runtime.CompilerServices.SkipLocalsInitAttribute";
}
}