Add validation that the StackBufferSize member exists when a stackall…

…oc constructor exists. (#125)

DllImportGenerator/DllImportGenerator.Test/ManualTypeMarshallingAnalyzerTests.cs

@@ -564,6 +564,8 @@ class S
 struct Native
 {
     public Native(S s, Span<byte> buffer) {}
+
+    public const int StackBufferSize = 0x100;
 }";
 
             await VerifyCS.VerifyAnalyzerAsync(source,
@@ -589,6 +591,8 @@ struct Native
     public Native(S s, Span<byte> buffer) {}
 
     public IntPtr Value => IntPtr.Zero;
+    
+    public const int StackBufferSize = 0x100;
 }";
 
             await VerifyCS.VerifyAnalyzerAsync(source,
@@ -1046,5 +1050,29 @@ struct G<T, U> where U : class
 }";
             await VerifyCS.VerifyAnalyzerAsync(source);
         }
+
+        [Fact]
+        public async Task NativeTypeWithStackallocConstructorWithoutBufferSize_ReportsDiagnostic()
+        {
+            string source = @"
+using System;
+using System.Runtime.InteropServices;
+
+[NativeMarshalling(typeof(Native))]
+class S
+{
+    public byte c;
+}
+
+[BlittableType]
+struct Native
+{
+    public Native(S s) {}
+    public Native(S s, Span<byte> buffer) {}
+}";
+
+            await VerifyCS.VerifyAnalyzerAsync(source,
+                VerifyCS.Diagnostic(StackallocConstructorMustHaveStackBufferSizeConstantRule).WithSpan(15, 5, 15, 45).WithArguments("Native"));
+        }
     }
 }

DllImportGenerator/DllImportGenerator/ManualTypeMarshallingAnalyzer.cs

@@ -124,6 +124,16 @@ public class ManualTypeMarshallingAnalyzer : DiagnosticAnalyzer
                 isEnabledByDefault: true,
                 description: new LocalizableResourceString(nameof(Resources.StackallocMarshallingShouldSupportAllocatingMarshallingFallbackDescription), Resources.ResourceManager, typeof(Resources)));
 
+        public readonly static DiagnosticDescriptor StackallocConstructorMustHaveStackBufferSizeConstantRule =
+            new DiagnosticDescriptor(
+                "INTEROPGEN012",
+                "StackallocConstructorMustHaveStackBufferSizeConstant",
+                new LocalizableResourceString(nameof(Resources.StackallocConstructorMustHaveStackBufferSizeConstantMessage), Resources.ResourceManager, typeof(Resources)),
+                Category,
+                DiagnosticSeverity.Error,
+                isEnabledByDefault: true,
+                description: new LocalizableResourceString(nameof(Resources.StackallocConstructorMustHaveStackBufferSizeConstantDescription), Resources.ResourceManager, typeof(Resources)));
+
         public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => 
             ImmutableArray.Create(
                 BlittableTypeMustBeBlittableRule,
@@ -136,7 +146,8 @@ public class ManualTypeMarshallingAnalyzer : DiagnosticAnalyzer
                 ValuePropertyMustHaveSetterRule,
                 ValuePropertyMustHaveGetterRule,
                 GetPinnableReferenceShouldSupportAllocatingMarshallingFallbackRule,
-                StackallocMarshallingShouldSupportAllocatingMarshallingFallbackRule);
+                StackallocMarshallingShouldSupportAllocatingMarshallingFallbackRule,
+                StackallocConstructorMustHaveStackBufferSizeConstantRule);
 
         public override void Initialize(AnalysisContext context)
         {
@@ -309,6 +320,11 @@ private void AnalyzeNativeMarshalerType(SymbolAnalysisContext context, ITypeSymb
                                                     && SymbolEqualityComparer.Default.Equals(SpanOfByte, ctor.Parameters[1].Type))
                     {
                         hasStackallocConstructor = true;
+                        IFieldSymbol stackAllocSizeField = nativeType.GetMembers("StackBufferSize").OfType<IFieldSymbol>().FirstOrDefault();
+                        if (stackAllocSizeField is null or { DeclaredAccessibility: not Accessibility.Public } or { IsConst: false } or { Type: not { SpecialType: SpecialType.System_Int32 } })
+                        {
+                            context.ReportDiagnostic(Diagnostic.Create(StackallocConstructorMustHaveStackBufferSizeConstantRule, ctor.DeclaringSyntaxReferences[0].GetSyntax()!.GetLocation(), nativeType.ToDisplayString()));
+                        }
                     }
                 }
 

DllImportGenerator/DllImportGenerator/Resources.resx

@@ -165,6 +165,12 @@
   <data name="NativeTypeMustHaveRequiredShapeMessage" xml:space="preserve">
     <value>The native type '{0}' must be a value type and have a constructor that takes one parameter of type '{1}' or a parameterless instance method named 'ToManaged' that returns '{1}'.</value>
   </data>
+  <data name="StackallocConstructorMustHaveStackBufferSizeConstantDescription" xml:space="preserve">
+    <value>When constructor taking a Span&lt;byte&gt; is specified on the native type, the type must also have a public integer constant named StackBufferSize to provide the size of the stack-allocated buffer.</value>
+  </data>
+  <data name="StackallocConstructorMustHaveStackBufferSizeConstantMessage" xml:space="preserve">
+    <value>The native type '{0}' must have a 'public const int StackBufferSize' field that specifies the size of the stack buffer because it has a constructor that takes a stack-allocated Span&lt;byte&gt;.</value>
+  </data>
   <data name="StackallocMarshallingShouldSupportAllocatingMarshallingFallbackDescription" xml:space="preserve">
     <value>A type that supports marshalling from managed to native by stack allocation should also support marshalling from managed to native where stack allocation is impossible.</value>
   </data>

DllImportGenerator/designs/StructMarshalling.md

@@ -76,7 +76,7 @@ partial struct TNative
 {
      public TNative(TManaged managed, Span<byte> stackSpace) {}
 
-     public static const int StackBufferSize = /* */;
+     public const int StackBufferSize = /* */;
 }
 ```