Implement infra to support marshalling blittable generics (equivalent to .NET 5 support)

DllImportGenerator/Ancillary.Interop/GeneratedMarshallingAttribute.cs

@@ -11,6 +11,22 @@ class GeneratedMarshallingAttribute : Attribute
     public class BlittableTypeAttribute : Attribute
     {
     }
+
+    [AttributeUsage(AttributeTargets.Struct)]
+    public class BlittableTypeIfGenericParametersBlittableAttribute : Attribute
+    {
+        public BlittableTypeIfGenericParametersBlittableAttribute()
+        {
+        }
+    }
+
+    [AttributeUsage(AttributeTargets.GenericParameter)]
+    public class ContributesToBlittabilityAttribute : Attribute
+    {
+        public ContributesToBlittabilityAttribute()
+        {
+        }
+    }
 
     [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class)]
     public class NativeMarshallingAttribute : Attribute

DllImportGenerator/DllImportGenerator.Test/ManualTypeMarshallingAnalyzerTests.cs

@@ -140,7 +140,6 @@ struct T
 }
 ";
             await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(BlittableTypeMustBeBlittableRule).WithSpan(4, 2, 4, 15).WithArguments("S"),
                 VerifyCS.Diagnostic(BlittableTypeMustBeBlittableRule).WithSpan(10, 2, 10, 15).WithArguments("T"));
         }
 
@@ -243,7 +242,7 @@ public Native(S s)
     public S ToManaged() => new S();
 }";
             await VerifyCS.VerifyAnalyzerAsync(source,
-                VerifyCS.Diagnostic(NativeTypeMustBeBlittableRule).WithSpan(11, 1, 20, 2).WithArguments("Native", "S"));
+                VerifyCS.Diagnostic(NativeTypeMustHaveRequiredShapeRule).WithSpan(11, 1, 20, 2).WithArguments("Native", "S"));
         }
 
         [Fact]
@@ -970,5 +969,153 @@ unsafe struct S
 }";
             await VerifyCS.VerifyAnalyzerAsync(source);
         }
+
+        [Fact]
+        public async Task BlittableGenericTypeInBlittableType_DoesNotReportDiagnostic()
+        {
+
+            var source = @"
+using System.Runtime.InteropServices;
+
+[BlittableTypeIfGenericParametersBlittable]
+struct G<[ContributesToBlittability] T>
+{
+    T fld;
+}
+
+[BlittableType]
+unsafe struct S
+{
+    private G<int> field;
+}";
+            await VerifyCS.VerifyAnalyzerAsync(source);
+        }
+
+        [Fact]
+        public async Task NonBlittableGenericTypeInBlittableType_ReportsDiagnostic()
+        {
+            var source = @"
+using System.Runtime.InteropServices;
+
+[BlittableTypeIfGenericParametersBlittable]
+struct G<[ContributesToBlittability] T>
+{
+    T fld;
+}
+
+[BlittableType]
+unsafe struct S
+{
+    private G<string> field;
+}";
+            await VerifyCS.VerifyAnalyzerAsync(source,
+                VerifyCS.Diagnostic(BlittableTypeMustBeBlittableRule).WithSpan(10, 2, 10, 15).WithArguments("S"));
+        }
+
+        [Fact]
+        public async Task BlittableTypeIfGenericParametersBlittableOnNonGenericType_ReportsDiagnostic()
+        {
+            var source = @"
+using System.Runtime.InteropServices;
+
+[BlittableTypeIfGenericParametersBlittable]
+struct G
+{
+    int fld;
+}";
+            await VerifyCS.VerifyAnalyzerAsync(source,
+                VerifyCS.Diagnostic(BlittableTypeIfGenericParametersBlittableInvalidTargetRule).WithSpan(4, 2, 4, 43).WithArguments("G"));
+        }
+
+        [Fact]
+        public async Task ConditionallyBlittableGenericTypeWithNonContributesToBlittability_ReportsDiagnostic()
+        {   
+            var source = @"
+using System.Runtime.InteropServices;
+
+[BlittableTypeIfGenericParametersBlittable]
+struct G<[ContributesToBlittability] T, U>
+{
+    T fld;
+    U fld2;
+}";
+            await VerifyCS.VerifyAnalyzerAsync(source,
+                VerifyCS.Diagnostic(ConditionallyBlittableTypeMustBeConditionallyBlittableRule).WithSpan(4, 2, 4, 43).WithArguments("G<T, U>"));
+        }
+
+        [Fact]
+        public async Task ConditionallyBlittableGenericTypeConditionalTypeParameterReferenceType_ReportsDiagnostic()
+        {
+            var source = @"
+using System.Runtime.InteropServices;
+
+[BlittableTypeIfGenericParametersBlittable]
+struct G<[ContributesToBlittability] T> where T : class
+{
+    T fld;
+}";
+            await VerifyCS.VerifyAnalyzerAsync(source,
+                VerifyCS.Diagnostic(ReferenceTypeParameterCanNeverBeBlittableRule).WithSpan(5, 11, 5, 36).WithArguments("T"),
+                VerifyCS.Diagnostic(ConditionallyBlittableTypeMustBeConditionallyBlittableRule).WithSpan(4, 2, 4, 43).WithArguments("G<T>"));
+        }
+
+        [Fact]
+        public async Task ConditionallyBlittableGenericTypeContainingConditionallyGenericType_DoesNotReportDiagnostic()
+        {
+            var source = @"
+using System.Runtime.InteropServices;
+
+[BlittableTypeIfGenericParametersBlittable]
+struct G<[ContributesToBlittability] T>
+{
+    T fld;
+}
+
+[BlittableTypeIfGenericParametersBlittable]
+struct F<[ContributesToBlittability] T>
+{
+    G<T> fld;
+}
+";
+            await VerifyCS.VerifyAnalyzerAsync(source);
+        }
+
+        [Fact]
+        public async Task ConditionallyBlittableNestedGenericType_DoesNotReportDiagnostic()
+        {
+            var source = @"
+using System.Runtime.InteropServices;
+
+struct C<[ContributesToBlittability] T>
+{
+    [BlittableTypeIfGenericParametersBlittable]
+    struct G
+    {
+        T fld;
+    }
+}
+";
+            await VerifyCS.VerifyAnalyzerAsync(source);
+        }
+
+        [Fact]
+        public async Task ConditionallyBlittableNestedGenericTypeWithReferenceTypeGenericParameter_DoesNotReportDiagnostic()
+        {
+            var source = @"
+using System.Runtime.InteropServices;
+
+struct C<[ContributesToBlittability] T> where T : class
+{
+    [BlittableTypeIfGenericParametersBlittable]
+    struct G
+    {
+        T fld;
+    }
+}
+";
+            await VerifyCS.VerifyAnalyzerAsync(source,
+                VerifyCS.Diagnostic(ReferenceTypeParameterCanNeverBeBlittableRule).WithSpan(4, 11, 4, 36).WithArguments("T"),
+                VerifyCS.Diagnostic(ConditionallyBlittableTypeMustBeConditionallyBlittableRule).WithSpan(6, 6, 6, 47).WithArguments("C<T>.G"));
+        }
     }
 }