Fix edge cases of getting attribute data from syntax

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/Analyzers/SyntaxExtensions.cs

@@ -33,7 +33,17 @@ public static Location FindTypeExpressionOrNullLocation(this AttributeArgumentSy
                 switch (attributeTarget.Identifier.Kind())
                 {
                     case SyntaxKind.ReturnKeyword:
-                        return ((IMethodSymbol)targetSymbol).GetReturnTypeAttributes().First(attributeSyntaxLocationMatches);
+                        if (targetSymbol is IMethodSymbol method)
+                        {
+                            // Sometimes an attribute is put on a symbol that is nested within the containing symbol.
+                            // For example, the ContainingSymbol for an AttributeSyntax on a local function has a ContainingSymbol of the method.
+                            // Since this method is internal and the callers don't care about attributes on local functions,
+                            // we just allow this method to return null in those cases.
+                            return method.GetReturnTypeAttributes().FirstOrDefault(attributeSyntaxLocationMatches);
+                        }
+                        // An attribute on the return value of a delegate type's Invoke method has a ContainingSymbol of the delegate type.
+                        // We don't care about the attributes in this case for the callers, so we'll just return null.
+                        return null;
                     case SyntaxKind.AssemblyKeyword:
                         return targetSymbol.ContainingAssembly.GetAttributes().First(attributeSyntaxLocationMatches);
                     case SyntaxKind.ModuleKeyword:
@@ -43,7 +53,8 @@ public static Location FindTypeExpressionOrNullLocation(this AttributeArgumentSy
                 }
             }
             // Sometimes an attribute is put on a symbol that is nested within the containing symbol.
-            // For example, the ContainingSymbol for an AttributeSyntax on a parameter have a ContainingSymbol of the method.
+            // For example, the ContainingSymbol for an AttributeSyntax on a parameter has a ContainingSymbol of the method
+            // and an AttributeSyntax on a local function has a ContainingSymbol of the containing method.
             // Since this method is internal and the callers don't care about attributes on parameters, we just allow
             // this method to return null in those cases.
             return targetSymbol.GetAttributes().FirstOrDefault(attributeSyntaxLocationMatches);

src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/NativeMarshallingAttributeAnalyzerTests.cs

@@ -272,8 +272,18 @@ public class X
                 {
                     void Foo([MarshalAs(UnmanagedType.I4)] int i)
                     {
+                        [return:MarshalAs(UnmanagedType.I4)]
+                        [SkipLocalsInit]
+                        static int Local()
+                        {
+                            return 0;
+                        }
                     }
                 }
+
+                [return:MarshalAs(UnmanagedType.I4)]
+                delegate int Y();
+
                 """;
 
             await VerifyCS.VerifyAnalyzerAsync(source);