add DoesAssetExist to support the upcoming Stardew Valley 1.6 (#766)

src/SMAPI/Framework/ContentCoordinator.cs

@@ -296,6 +296,22 @@ namespace StardewModdingAPI.Framework
             return Path.Combine(this.ManagedPrefix, modID.ToLower());
         }
 
+        /// <summary>Get whether an asset from a mod folder exists.</summary>
+        /// <param name="contentManagerID">The unique name for the content manager which should load this asset.</param>
+        /// <param name="assetName">The asset name within the mod folder.</param>
+        public bool DoesManagedAssetExist(string contentManagerID, IAssetName assetName)
+        {
+            // get content manager
+            IContentManager contentManager = this.ContentManagerLock.InReadLock(() =>
+                this.ContentManagers.FirstOrDefault(p => p.IsNamespaced && p.Name == contentManagerID)
+            );
+            if (contentManager == null)
+                throw new InvalidOperationException($"The '{contentManagerID}' prefix isn't handled by any mod.");
+
+            // get whether the asset exists
+            return contentManager.DoesAssetExist(assetName);
+        }
+
         /// <summary>Get a copy of an asset from a mod folder.</summary>
         /// <typeparam name="T">The asset type.</typeparam>
         /// <param name="contentManagerID">The unique name for the content manager which should load this asset.</param>

src/SMAPI/Framework/ContentManagers/BaseContentManager.cs

@@ -92,6 +92,12 @@ namespace StardewModdingAPI.Framework.ContentManagers
             this.BaseDisposableReferences = reflection.GetField<List<IDisposable>>(this, "disposableAssets").GetValue();
         }
 
+        /// <inheritdoc />
+        public virtual bool DoesAssetExist(IAssetName assetName)
+        {
+            return this.Cache.ContainsKey(assetName.Name);
+        }
+
         /// <inheritdoc />
         [Obsolete("This method is implemented for the base game and should not be used directly. To load an asset from the underlying content manager directly, use " + nameof(BaseContentManager.RawLoad) + " instead.")]
         public override T LoadBase<T>(string assetName)

src/SMAPI/Framework/ContentManagers/GameContentManager.cs

@@ -62,6 +62,29 @@ namespace StardewModdingAPI.Framework.ContentManagers
             this.OnLoadingFirstAsset = onLoadingFirstAsset;
         }
 
+        /// <inheritdoc />
+        public override bool DoesAssetExist(IAssetName assetName)
+        {
+            if (base.DoesAssetExist(assetName))
+                return true;
+
+            // managed asset
+            if (this.Coordinator.TryParseManagedAssetKey(assetName.Name, out string contentManagerID, out IAssetName relativePath))
+                return this.Coordinator.DoesManagedAssetExist(contentManagerID, relativePath);
+
+            // else check for loaders
+            string locale = this.GetLocale();
+            IAssetInfo info = new AssetInfo(locale, assetName, typeof(object), this.AssertAndNormalizeAssetName);
+            ModLinked<IAssetLoader>[] loaders = this.GetLoaders<object>(info).ToArray();
+            if (loaders.Length > 1)
+            {
+                string[] loaderNames = loaders.Select(p => p.Mod.DisplayName).ToArray();
+                this.Monitor.Log($"Multiple mods want to provide the '{info.Name}' asset ({string.Join(", ", loaderNames)}), but an asset can't be loaded multiple times. SMAPI will use the default asset instead; uninstall one of the mods to fix this. (Message for modders: you should usually use {typeof(IAssetEditor)} instead to avoid conflicts.)", LogLevel.Warn);
+            }
+
+            return loaders.Length == 1;
+        }
+
         /// <inheritdoc />
         public override T Load<T>(IAssetName assetName, LanguageCode language, bool useCache)
         {
@@ -246,20 +269,7 @@ namespace StardewModdingAPI.Framework.ContentManagers
         private IAssetData ApplyLoader<T>(IAssetInfo info)
         {
             // find matching loaders
-            var loaders = this.Loaders
-                .Where(entry =>
-                {
-                    try
-                    {
-                        return entry.Data.CanLoad<T>(info);
-                    }
-                    catch (Exception ex)
-                    {
-                        entry.Mod.LogAsMod($"Mod failed when checking whether it could load asset '{info.Name}', and will be ignored. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
-                        return false;
-                    }
-                })
-                .ToArray();
+            var loaders = this.GetLoaders<T>(info).ToArray();
 
             // validate loaders
             if (!loaders.Any())
@@ -360,6 +370,26 @@ namespace StardewModdingAPI.Framework.ContentManagers
             return asset;
         }
 
+        /// <summary>Get the asset loaders which handle the asset.</summary>
+        /// <typeparam name="T">The asset type.</typeparam>
+        /// <param name="info">The basic asset metadata.</param>
+        private IEnumerable<ModLinked<IAssetLoader>> GetLoaders<T>(IAssetInfo info)
+        {
+            return this.Loaders
+                .Where(entry =>
+                {
+                    try
+                    {
+                        return entry.Data.CanLoad<T>(info);
+                    }
+                    catch (Exception ex)
+                    {
+                        entry.Mod.LogAsMod($"Mod failed when checking whether it could load asset '{info.Name}', and will be ignored. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
+                        return false;
+                    }
+                });
+        }
+
         /// <summary>Validate that an asset loaded by a mod is valid and won't cause issues, and fix issues if possible.</summary>
         /// <typeparam name="T">The asset type.</typeparam>
         /// <param name="info">The basic asset metadata.</param>

src/SMAPI/Framework/ContentManagers/IContentManager.cs

@@ -28,6 +28,10 @@ namespace StardewModdingAPI.Framework.ContentManagers
         /*********
         ** Methods
         *********/
+        /// <summary>Get whether an asset exists and can be loaded.</summary>
+        /// <param name="assetName">The normalized asset name.</param>
+        bool DoesAssetExist(IAssetName assetName);
+
         /// <summary>Load an asset that has been processed by the content pipeline.</summary>
         /// <typeparam name="T">The type of asset to load.</typeparam>
         /// <param name="assetName">The asset name relative to the loader root directory.</param>

src/SMAPI/Framework/ContentManagers/ModContentManager.cs

@@ -63,6 +63,16 @@ namespace StardewModdingAPI.Framework.ContentManagers
             this.ModName = modName;
         }
 
+        /// <inheritdoc />
+        public override bool DoesAssetExist(IAssetName assetName)
+        {
+            if (base.DoesAssetExist(assetName))
+                return true;
+
+            FileInfo file = this.GetModFile(assetName.Name);
+            return file.Exists;
+        }
+
         /// <inheritdoc />
         public override T Load<T>(string assetName)
         {