Fix assertions and crashes encountered when inferring types for ICSharpCode.Decompiler.

Author: dgrunwald

NullabilityInference.Tests/InferenceTests.cs

@@ -1270,6 +1270,22 @@ public T Test<T>()
 
         T Get() => default;
     }
+}");
+        }
+
+        [Fact]
+        public void FixedFieldAccess()
+        {
+            AssertNullabilityInference(@"
+internal unsafe struct IMAGE_RESOURCE_DIRECTORY_STRING
+{
+    public ushort Length;
+    public fixed char NameString[1];
+}
+unsafe class Program {
+    public bool Test(IMAGE_RESOURCE_DIRECTORY_STRING* ptr) {
+        return ptr->NameString == null;
+    }
 }");
         }
     }

NullabilityInference/EdgeBuildingOperationVisitor.cs

@@ -1093,22 +1093,25 @@ private List<TypeWithNode> HandleArguments(TypeSubstitution substitution, Immuta
 
         public override TypeWithNode VisitObjectCreation(IObjectCreationOperation operation, EdgeBuildingContext argument)
         {
+            TypeWithNode newObjectType;
             if (operation.Syntax is ObjectCreationExpressionSyntax syntax) {
-                var newObjectType = syntax.Type.Accept(syntaxVisitor).WithNode(typeSystem.NonNullNode);
-                var substitution = new TypeSubstitution(newObjectType.TypeArguments, new TypeWithNode[0]);
-                HandleArguments(substitution, operation.Arguments, invocationContext: argument);
-
-                var oldObjectCreationType = currentObjectCreationType;
-                try {
-                    currentObjectCreationType = newObjectType;
-                    operation.Initializer?.Accept(this, EdgeBuildingContext.Normal);
-                } finally {
-                    currentObjectCreationType = oldObjectCreationType;
-                }
-                return newObjectType;
+                newObjectType = syntax.Type.Accept(syntaxVisitor).WithNode(typeSystem.NonNullNode);
+            } else if (operation.Syntax is ImplicitObjectCreationExpressionSyntax) {
+                newObjectType = tsBuilder.CreateHelperType(operation.Type);
             } else {
                 throw new NotImplementedException($"ObjectCreationOperation with syntax={operation.Syntax}");
             }
+            var substitution = new TypeSubstitution(newObjectType.TypeArguments, new TypeWithNode[0]);
+            HandleArguments(substitution, operation.Arguments, invocationContext: argument);
+
+            var oldObjectCreationType = currentObjectCreationType;
+            try {
+                currentObjectCreationType = newObjectType;
+                operation.Initializer?.Accept(this, EdgeBuildingContext.Normal);
+            } finally {
+                currentObjectCreationType = oldObjectCreationType;
+            }
+            return newObjectType;
         }
 
         public override TypeWithNode VisitTypeParameterObjectCreation(ITypeParameterObjectCreationOperation operation, EdgeBuildingContext argument)
@@ -1790,6 +1793,18 @@ public override TypeWithNode VisitConstantPattern(IConstantPatternOperation oper
             return typeSystem.GetObliviousType(operation.Type);
         }
 
+        public override TypeWithNode VisitRelationalPattern(IRelationalPatternOperation operation, EdgeBuildingContext argument)
+        {
+            Visit(operation.Value, EdgeBuildingContext.Normal);
+            return typeSystem.GetObliviousType(operation.Type);
+        }
+
+        public override TypeWithNode VisitNegatedPattern(INegatedPatternOperation operation, EdgeBuildingContext argument)
+        {
+            Visit(operation.Pattern, EdgeBuildingContext.Normal);
+            return typeSystem.GetObliviousType(operation.Type);
+        }
+
         public override TypeWithNode VisitAddressOf(IAddressOfOperation operation, EdgeBuildingContext argument)
         {
             Visit(operation.Reference, EdgeBuildingContext.LValue);

NullabilityInference/EdgeBuildingSyntaxVisitor.cs

@@ -447,5 +447,12 @@ internal bool IsReducedExtensionMethodCall(InvocationExpressionSyntax invocation
             var symbolInfo = semanticModel.GetSymbolInfo(invocation, cancellationToken);
             return symbolInfo.Symbol is IMethodSymbol { MethodKind: MethodKind.ReducedExtension };
         }
+
+        public override TypeWithNode VisitVariableDeclarator(VariableDeclaratorSyntax node)
+        {
+            // skip node.ArgumentList (array size of fixed field), it doesn't have an associated operation
+            node.Initializer?.Accept(this);
+            return typeSystem.VoidType;
+        }
     }
 }

NullabilityInference/NodeBuildingSyntaxVisitor.cs

@@ -189,7 +189,13 @@ public override TypeWithNode VisitVariableDeclaration(VariableDeclarationSyntax
                 foreach (var v in node.Variables) {
                     var symbol = semanticModel.GetDeclaredSymbol(v, cancellationToken);
                     if (symbol != null) {
-                        typeSystem.AddSymbolType(symbol, type);
+                        if (v.ArgumentList != null && symbol is IFieldSymbol f) {
+                            // field field
+                            var arrayType = new TypeWithNode(f.Type, typeSystem.ObliviousNode, new[] { type });
+                            typeSystem.AddSymbolType(symbol, arrayType);
+                        } else {
+                            typeSystem.AddSymbolType(symbol, type);
+                        }
                     }
                 }
             }
@@ -252,6 +258,8 @@ public override TypeWithNode VisitRecursivePattern(RecursivePatternSyntax node)
                         throw new NotImplementedException($"DeclarationPattern with explicit type unsupported designation: {node.Designation} near {node.GetLocation().StartPosToString()}");
                     }
                 }
+            } else {
+                node.Designation?.Accept(this);
             }
             node.PositionalPatternClause?.Accept(this);
             node.PropertyPatternClause?.Accept(this);
@@ -313,7 +321,7 @@ private bool CanUseOutParamFlow(IMethodSymbol? method)
             }
             return method.EffectiveReturnType().SpecialType == SpecialType.System_Boolean;
         }
-        
+
 
         public override TypeWithNode VisitNameMemberCref(NameMemberCrefSyntax node)
         {