rewrite HarmonyMethod to allow null (#711)

src/SMAPI/Framework/ModLoading/Framework/RewriteHelper.cs

@@ -137,7 +137,7 @@ namespace StardewModdingAPI.Framework.ModLoading.Framework
         /// <summary>Get whether a method definition matches the signature expected by a method reference.</summary>
         /// <param name="definition">The method definition.</param>
         /// <param name="reference">The method reference.</param>
-        public static bool HasMatchingSignature(MethodInfo definition, MethodReference reference)
+        public static bool HasMatchingSignature(MethodBase definition, MethodReference reference)
         {
             // 
             // duplicated by HasMatchingSignature(MethodDefinition, MethodReference) below
@@ -166,7 +166,7 @@ namespace StardewModdingAPI.Framework.ModLoading.Framework
         public static bool HasMatchingSignature(MethodDefinition definition, MethodReference reference)
         {
             // 
-            // duplicated by HasMatchingSignature(MethodInfo, MethodReference) above
+            // duplicated by HasMatchingSignature(MethodBase, MethodReference) above
             //
 
             // same name
@@ -191,6 +191,13 @@ namespace StardewModdingAPI.Framework.ModLoading.Framework
         /// <param name="reference">The method reference.</param>
         public static bool HasMatchingSignature(Type type, MethodReference reference)
         {
+            if (reference.Name == ".ctor")
+            {
+                return type
+                    .GetConstructors(BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly | BindingFlags.Public)
+                    .Any(method => RewriteHelper.HasMatchingSignature(method, reference));
+            }
+
             return type
                 .GetMethods(BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly | BindingFlags.Public)
                 .Any(method => RewriteHelper.HasMatchingSignature(method, reference));

src/SMAPI/Framework/ModLoading/RewriteFacades/HarmonyMethodFacade.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Reflection;
+using HarmonyLib;
+
+namespace StardewModdingAPI.Framework.ModLoading.RewriteFacades
+{
+    /// <summary>Maps Harmony 1.x <see cref="HarmonyMethod"/> methods to Harmony 2.x to avoid breaking older mods.</summary>
+    /// <remarks>This is public to support SMAPI rewriting and should not be referenced directly by mods.</remarks>
+    [SuppressMessage("ReSharper", "UnusedMember.Global", Justification = "Used via assembly rewriting")]
+    [SuppressMessage("ReSharper", "CS1591", Justification = "Documentation not needed for facade classes.")]
+    public class HarmonyMethodFacade : HarmonyMethod
+    {
+        /*********
+        ** Public methods
+        *********/
+        public HarmonyMethodFacade(MethodInfo method)
+        {
+            this.ImportMethodImpl(method);
+        }
+
+        public HarmonyMethodFacade(Type type, string name, Type[] parameters = null)
+        {
+            this.ImportMethodImpl(AccessTools.Method(type, name, parameters));
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Import a method directly using the internal HarmonyMethod code.</summary>
+        /// <param name="methodInfo">The method to import.</param>
+        private void ImportMethodImpl(MethodInfo methodInfo)
+        {
+            // A null method is no longer allowed in the constructor with Harmony 2.0, but the
+            // internal code still handles null fine. For backwards compatibility, this bypasses
+            // the new restriction when the mod hasn't been updated for Harmony 2.0 yet.
+
+            MethodInfo importMethod = typeof(HarmonyMethod).GetMethod("ImportMethod", BindingFlags.Instance | BindingFlags.NonPublic);
+            if (importMethod == null)
+                throw new InvalidOperationException("Can't find 'HarmonyMethod.ImportMethod' method");
+            importMethod.Invoke(this, new object[] { methodInfo });
+        }
+    }
+}

src/SMAPI/Framework/ModLoading/Rewriters/Harmony1AssemblyRewriter.cs

@@ -92,6 +92,10 @@ namespace StardewModdingAPI.Framework.ModLoading.Rewriters
                     toType = typeof(AccessToolsFacade);
                     break;
 
+                case "HarmonyLib.HarmonyMethod":
+                    toType = typeof(HarmonyMethodFacade);
+                    break;
+
                 default:
                     return false;
             }