From d9874380cde97604a7975f1afa75c79c41fbef3b Mon Sep 17 00:00:00 2001
From: Daniel Grunwald <daniel@danielgrunwald.de>
Date: Tue, 29 Dec 2020 18:26:30 +0100
Subject: [PATCH] Records: support generic records

---
 .../TestCases/Pretty/Records.cs               | 18 ++++++++++++++++++
 .../CSharp/RecordDecompiler.cs                | 19 ++++++++++++++-----
 .../CSharp/Syntax/TypeSystemAstBuilder.cs     |  2 +-
 .../TypeSystem/TypeSystemExtensions.cs        | 17 +++++++++++++++++
 4 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/Records.cs b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/Records.cs
index 07865dc19..bba7d911b 100644
--- a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/Records.cs
+++ b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/Records.cs
@@ -13,6 +13,18 @@
 		public string S = "abc";
 	}
 
+	public record Pair<A, B>
+	{
+		public A First {
+			get; 
+			init; 
+		}
+		public B Second { 
+			get; 
+			init; 
+		}
+	}
+
 	public record Properties
 	{
 		public int A { 
@@ -42,3 +54,9 @@
 		}
 	}
 }
+namespace System.Runtime.CompilerServices
+{
+	internal class IsExternalInit
+	{
+	}
+}
diff --git a/ICSharpCode.Decompiler/CSharp/RecordDecompiler.cs b/ICSharpCode.Decompiler/CSharp/RecordDecompiler.cs
index da7d74b49..25f80ed02 100644
--- a/ICSharpCode.Decompiler/CSharp/RecordDecompiler.cs
+++ b/ICSharpCode.Decompiler/CSharp/RecordDecompiler.cs
@@ -53,9 +53,11 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		void DetectAutomaticProperties()
 		{
-			foreach (var p in recordTypeDef.Properties)
+			var subst = recordTypeDef.AsParameterizedType().GetSubstitution();
+			foreach (var property in recordTypeDef.Properties)
 			{
 				cancellationToken.ThrowIfCancellationRequested();
+				var p = (IProperty)property.Specialize(subst);
 				if (IsAutoProperty(p, out var field))
 				{
 					backingFieldToAutoProperty.Add(field, p);
@@ -152,8 +154,9 @@ namespace ICSharpCode.Decompiler.CSharp
 			// need to detect the correct interleaving.
 			// We could try to detect this from the PrintMembers body, but let's initially
 			// restrict ourselves to the common case where the record only uses properties.
-			return recordTypeDef.Properties.Concat<IMember>(
-				recordTypeDef.Fields.Where(f => !backingFieldToAutoProperty.ContainsKey(f))
+			var subst = recordTypeDef.AsParameterizedType().GetSubstitution();
+			return recordTypeDef.Properties.Select(p => p.Specialize(subst)).Concat(
+				recordTypeDef.Fields.Select(f => (IField)f.Specialize(subst)).Where(f => !backingFieldToAutoProperty.ContainsKey(f))
 			).ToList();
 		}
 
@@ -417,9 +420,15 @@ namespace ICSharpCode.Decompiler.CSharp
 						val = addressOf.Value;
 					}
 				}
+				else if (val is Box box)
+				{
+					if (!NormalizeTypeVisitor.TypeErasure.EquivalentTypes(box.Type, member.ReturnType))
+						return false;
+					val = box.Argument;
+				}
 				if (val is CallInstruction getterCall && member is IProperty property)
 				{
-					if (!getterCall.Method.MemberDefinition.Equals(property.Getter.MemberDefinition))
+					if (!getterCall.Method.Equals(property.Getter))
 						return false;
 					if (getterCall.Arguments.Count != 1)
 						return false;
@@ -430,7 +439,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				{
 					if (!target.MatchLdThis())
 						return false;
-					if (!field.MemberDefinition.Equals(member))
+					if (!field.Equals(member))
 						return false;
 				}
 				else
diff --git a/ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs b/ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs
index 08f87fa5a..1e04e5402 100644
--- a/ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs
+++ b/ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs
@@ -1804,7 +1804,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 					else if (SupportRecordClasses && typeDefinition.IsRecord
 						&& baseType.Name == "IEquatable" && baseType.Namespace == "System"
 						&& baseType.TypeArguments.Count == 1
-						&& baseType.TypeArguments[0].Equals(typeDefinition))
+						&& baseType.TypeArguments[0].Equals(typeDefinition.AsParameterizedType()))
 					{
 						// omit "IEquatable<R>" in records
 						continue;
diff --git a/ICSharpCode.Decompiler/TypeSystem/TypeSystemExtensions.cs b/ICSharpCode.Decompiler/TypeSystem/TypeSystemExtensions.cs
index bf25900b6..993804d95 100644
--- a/ICSharpCode.Decompiler/TypeSystem/TypeSystemExtensions.cs
+++ b/ICSharpCode.Decompiler/TypeSystem/TypeSystemExtensions.cs
@@ -616,5 +616,22 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			}
 			return null;
 		}
+
+		/// <summary>
+		/// When given a generic type definition, returns the self-parameterized type
+		/// (i.e. the type of "this" within the type definition).
+		/// When given a non-generic type definition, returns that definition unchanged.
+		/// </summary>
+		public static IType AsParameterizedType(this ITypeDefinition td)
+		{
+			if (td.TypeParameterCount == 0)
+			{
+				return td;
+			}
+			else
+			{
+				return new ParameterizedType(td, td.TypeArguments);
+			}
+		}
 	}
 }