Initial work on a way for mods to return specific API instances to specific mods.

src/SMAPI/Framework/ModHelpers/ModRegistryHelper.cs

@@ -1,5 +1,7 @@
+using System;
 using System.Collections.Generic;
 using StardewModdingAPI.Framework.Reflection;
+using StardewModdingAPI.Internal;
 
 namespace StardewModdingAPI.Framework.ModHelpers
 {
@@ -15,8 +17,8 @@ namespace StardewModdingAPI.Framework.ModHelpers
         /// <summary>Encapsulates monitoring and logging for the mod.</summary>
         private readonly IMonitor Monitor;
 
-        /// <summary>The mod IDs for APIs accessed by this instanced.</summary>
-        private readonly HashSet<string> AccessedModApis = new();
+        /// <summary>The APIs accessed by this instance.</summary>
+        private readonly Dictionary<string, object?> AccessedModApis = new();
 
         /// <summary>Generates proxy classes to access mod APIs through an arbitrary interface.</summary>
         private readonly IInterfaceProxyFactory ProxyFactory;
@@ -66,11 +68,50 @@ namespace StardewModdingAPI.Framework.ModHelpers
                 return null;
             }
 
-            // get raw API
+            // get our cached API if one is available
             IModMetadata? mod = this.Registry.Get(uniqueID);
-            if (mod?.Api != null && this.AccessedModApis.Add(mod.Manifest.UniqueID))
-                this.Monitor.Log($"Accessed mod-provided API for {mod.DisplayName}.");
-            return mod?.Api;
+            if (mod == null)
+                return null;
+
+            if (this.AccessedModApis.ContainsKey(mod.Manifest.UniqueID))
+            {
+                return this.AccessedModApis[mod.Manifest.UniqueID];
+            }
+
+            object? api;
+
+            // safely request a specific API instance
+            try
+            {
+                api = mod.Mod?.GetApi(this.Mod.Manifest);
+                if (api != null && !api.GetType().IsPublic)
+                {
+                    api = null;
+                    this.Monitor.Log($"{mod.DisplayName} provided a specific API instance with a non-public type. This isn't currently supported, so the specific API won't be available to the requesting mod.", LogLevel.Warn);
+                }
+
+                if (api != null)
+                    this.Monitor.Log($"Accessed specific mod-provided API ({api.GetType().FullName}) for {mod.DisplayName}.");
+            }
+            catch (Exception ex)
+            {
+                this.Monitor.Log($"Failed loading specific mod-provided API for {mod.DisplayName}. Integrations with other mods may not work. Error: {ex.GetLogSummary()}", LogLevel.Error);
+                api = null;
+            }
+
+            // fall back to the generic API instance
+            if (api == null)
+            {
+                api = mod.Api;
+                if (api != null)
+                {
+                    this.Monitor.Log($"Accessed mod-provided API for {mod.DisplayName}.");
+                }
+            }
+
+            // cache the API instance and return it
+            this.AccessedModApis[mod.Manifest.UniqueID] = api;
+            return api;
         }
 
         /// <inheritdoc />

src/SMAPI/IMod.cs

@@ -25,5 +25,11 @@ namespace StardewModdingAPI
 
         /// <summary>Get an API that other mods can access. This is always called after <see cref="Entry"/>.</summary>
         object? GetApi();
+
+        /// <summary>Get an API that a specific other mod can access. This method is called the first time the other mod calls <see cref="IModRegistry.GetApi(string)"/> for this mod.</summary>
+        /// <param name="manifest">The other mod's manifest.</param>
+        /// <returns>Returns an API for another mod, or <c>null</c> if the other mod should use the general API returned from <see cref="GetApi()"/>.</returns>
+        object? GetApi(IManifest manifest);
+
     }
 }

src/SMAPI/Mod.cs

@@ -30,6 +30,12 @@ namespace StardewModdingAPI
             return null;
         }
 
+        /// <inheritdoc />
+        public virtual object? GetApi(IManifest manifest)
+        {
+            return null;
+        }
+
         /// <summary>Release or reset unmanaged resources.</summary>
         public void Dispose()
         {