Added checking for alternative Steam library install locations when looking for the Stardew Valley install.

src/SMAPI.Toolkit/Framework/GameScanning/GameScanner.cs

@@ -9,6 +9,7 @@ using StardewModdingAPI.Toolkit.Utilities;
 using System.Reflection;
 #if SMAPI_FOR_WINDOWS
 using Microsoft.Win32;
+using VdfParser;
 #endif
 
 namespace StardewModdingAPI.Toolkit.Framework.GameScanning
@@ -158,7 +159,14 @@ namespace StardewModdingAPI.Toolkit.Framework.GameScanning
                         // via Steam library path
                         string? steamPath = this.GetCurrentUserRegistryValue(@"Software\Valve\Steam", "SteamPath");
                         if (steamPath != null)
+                        {
                             yield return Path.Combine(steamPath.Replace('/', '\\'), @"steamapps\common\Stardew Valley");
+
+                            // Check for Steam libraries in other locations
+                            string? path = this.GetPathFromSteamLibrary(steamPath);
+                            if (!string.IsNullOrWhiteSpace(path))
+                                yield return path;
+                        }
 #endif
 
                         // default GOG/Steam paths
@@ -243,6 +251,34 @@ namespace StardewModdingAPI.Toolkit.Framework.GameScanning
             using (openKey)
                 return (string?)openKey.GetValue(name);
         }
+
+        /// <summary>Get the game directory path from alternative Steam library locations.</summary>
+        /// <param name="steamPath">The full path to the directory containing steam.exe.</param>
+        /// <returns>The game directory, if found.</returns>
+        private string? GetPathFromSteamLibrary(string? steamPath)
+        {
+            string stardewAppId = "413150";
+            if (steamPath != null)
+            {
+                string? libraryFoldersPath = Path.Combine(steamPath.Replace('/', '\\'), "steamapps\\libraryfolders.vdf");
+                using FileStream fs = File.OpenRead(libraryFoldersPath);
+                VdfDeserializer deserializer = new VdfDeserializer();
+                SteamLibraryCollection libraries = deserializer.Deserialize<SteamLibraryCollection>(fs);
+                if (libraries.libraryfolders != null)
+                {
+                    var stardewLibrary = libraries.libraryfolders.FirstOrDefault(f =>
+                    {
+                        var apps = f.Value?.apps;
+                        return apps != null && apps.Any(a => a.Key.Equals(stardewAppId));
+                    });
+                    if (stardewLibrary.Value?.path != null)
+                    {
+                        return Path.Combine(stardewLibrary.Value.path.Replace("\\\\", "\\"), @"steamapps\common\Stardew Valley");
+                    }
+                }
+            }
+            return null;
+        }
 #endif
     }
 }

src/SMAPI.Toolkit/Framework/GameScanning/SteamLibraryCollection.cs

@@ -0,0 +1,47 @@
+#if SMAPI_FOR_WINDOWS
+using System.Collections.Generic;
+
+namespace StardewModdingAPI.Toolkit.Framework.GameScanning
+{
+#pragma warning disable IDE1006 // Model requires lowercase naming.
+#pragma warning disable CS8618 // Required for model.
+    /// <summary>Model for Steam's libraryfolders.vdf.</summary>
+    public class SteamLibraryCollection
+    {
+        /// <summary>Each entry identifies a different location that part of the Steam games library is installed to.</summary>
+        public LibraryFolders<int, LibraryFolder> libraryfolders { get; set; }
+    }
+
+    /// <summary>A collection of LibraryFolders. Like a dictionary, but has contentstatsid used as an index also.</summary>
+    /// <typeparam name="TKey"></typeparam>
+    /// <typeparam name="TValue"></typeparam>
+#pragma warning disable CS8714 // Required for model.
+    public class LibraryFolders<TKey, TValue> : Dictionary<TKey, TValue>
+#pragma warning restore CS8714
+    {
+        /// <summary>Index of the library, starting from "0".</summary>
+        public string contentstatsid { get; set; }
+    }
+
+    /// <summary>A Steam library folder, containing information on the location and size of games installed there.</summary>
+    public class LibraryFolder
+    {
+        /// <summary>The escaped path to this Steam library folder. There will be a steam.exe here, but this may not be the one the player generally launches.</summary>
+        public string path { get; set; }
+        /// <summary>Label for the library, or ""</summary>
+        public string label { get; set; }
+        /// <summary>~19-digit identifier.</summary>
+        public string contentid { get; set; }
+        /// <summary>Size of the library in bytes. May show 0 when size is non-zero.</summary>
+        public string totalsize { get; set; }
+        /// <summary>Used for downloads.</summary>
+        public string update_clean_bytes_tally { get; set; }
+        /// <summary>Normally "0".</summary>
+        public string time_last_update_corruption { get; set; }
+        /// <summary>List of Steam app IDs, and their current size in bytes.</summary>
+        public Dictionary<string, string> apps { get; set; }
+    }
+#pragma warning restore IDE1006
+#pragma warning restore CS8618
+}
+#endif

src/SMAPI.Toolkit/SMAPI.Toolkit.csproj

@@ -14,6 +14,7 @@
     <PackageReference Include="Pathoschild.Http.FluentClient" Version="4.1.1" />
     <PackageReference Include="System.Management" Version="5.0.0" Condition="'$(OS)' == 'Windows_NT'" />
     <PackageReference Include="Microsoft.Win32.Registry" Version="5.0.0" Condition="'$(OS)' == 'Windows_NT'" />
+    <PackageReference Include="VdfConverter" Version="1.0.3" />
   </ItemGroup>
 
   <ItemGroup>