1 files changed, 84 insertions, 0 deletions
diff --git a/src/SMAPI/Framework/ModLoading/RewriteFacades/HarmonyInstanceFacade.cs b/src/SMAPI/Framework/ModLoading/RewriteFacades/HarmonyInstanceFacade.cs
new file mode 100644
index 00000000..ad6d5e4f
--- /dev/null
+++ b/src/SMAPI/Framework/ModLoading/RewriteFacades/HarmonyInstanceFacade.cs
@@ -0,0 +1,84 @@
+#if HARMONY_2
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Reflection;
+using System.Reflection.Emit;
+using HarmonyLib;
+
+namespace StardewModdingAPI.Framework.ModLoading.RewriteFacades
+{
+    /// <summary>Maps Harmony 1.x <code>HarmonyInstance</code> methods to Harmony 2.x's <see cref="Harmony"/> 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 HarmonyInstanceFacade : Harmony
+    {
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="id">The unique patch identifier.</param>
+        public HarmonyInstanceFacade(string id)
+            : base(id) { }
+
+        public static Harmony Create(string id)
+        {
+            return new Harmony(id);
+        }
+
+        public DynamicMethod Patch(MethodBase original, HarmonyMethod prefix = null, HarmonyMethod postfix = null, HarmonyMethod transpiler = null)
+        {
+            // In Harmony 1.x you could target a virtual method that's not implemented by the
+            // target type, but in Harmony 2.0 you need to target the concrete implementation.
+            // This just resolves the method to the concrete implementation if needed.
+            if (original != null)
+                original = original.GetDeclaredMember();
+
+            // call Harmony 2.0 and show a detailed exception if it fails
+            try
+            {
+                MethodInfo method = base.Patch(original: original, prefix: prefix, postfix: postfix, transpiler: transpiler);
+                return (DynamicMethod)method;
+            }
+            catch (Exception ex)
+            {
+                string patchTypes = this.GetPatchTypesLabel(prefix, postfix, transpiler);
+                string methodLabel = this.GetMethodLabel(original);
+                throw new Exception($"Harmony instance {this.Id} failed applying {patchTypes} to {methodLabel}.", ex);
+            }
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Get a human-readable label for the patch types being applies.</summary>
+        /// <param name="prefix">The prefix method, if any.</param>
+        /// <param name="postfix">The postfix method, if any.</param>
+        /// <param name="transpiler">The transpiler method, if any.</param>
+        private string GetPatchTypesLabel(HarmonyMethod prefix = null, HarmonyMethod postfix = null, HarmonyMethod transpiler = null)
+        {
+            var patchTypes = new List<string>();
+
+            if (prefix != null)
+                patchTypes.Add("prefix");
+            if (postfix != null)
+                patchTypes.Add("postfix");
+            if (transpiler != null)
+                patchTypes.Add("transpiler");
+
+            return string.Join("/", patchTypes);
+        }
+
+        /// <summary>Get a human-readable label for the method being patched.</summary>
+        /// <param name="method">The method being patched.</param>
+        private string GetMethodLabel(MethodBase method)
+        {
+            return method != null
+                ? $"method {method.DeclaringType?.FullName}.{method.Name}"
+                : "null method";
+        }
+    }
+}
+#endif