add optional mod dependencies in SMAPI 2.0 (#287)

3 files changed, 38 insertions, 6 deletions

diff --git a/src/StardewModdingAPI/Framework/ModLoading/ModResolver.cs b/src/StardewModdingAPI/Framework/ModLoading/ModResolver.cs
index 9c56aaa4..38dddce7 100644
--- a/src/StardewModdingAPI/Framework/ModLoading/ModResolver.cs
+++ b/src/StardewModdingAPI/Framework/ModLoading/ModResolver.cs
@@ -228,13 +228,24 @@ namespace StardewModdingAPI.Framework.ModLoading
                     from entry in mod.Manifest.Dependencies
                     let dependencyMod = mods.FirstOrDefault(m => string.Equals(m.Manifest?.UniqueID, entry.UniqueID, StringComparison.InvariantCultureIgnoreCase))
                     orderby entry.UniqueID
-                    select new { ID = entry.UniqueID, MinVersion = entry.MinimumVersion, Mod = dependencyMod }
+                    select new
+                    {
+                        ID = entry.UniqueID,
+                        MinVersion = entry.MinimumVersion,
+                        Mod = dependencyMod,
+                        IsRequired =
+#if SMAPI_2_0
+                            entry.IsRequired
+#else
+                            true
+#endif
+                    }
                 )
                 .ToArray();
 
             // missing required dependencies, mark failed
             {
-                string[] failedIDs = (from entry in dependencies where entry.Mod == null select entry.ID).ToArray();
+                string[] failedIDs = (from entry in dependencies where entry.IsRequired && entry.Mod == null select entry.ID).ToArray();
                 if (failedIDs.Any())
                 {
                     sortedMods.Push(mod);
@@ -248,7 +259,7 @@ namespace StardewModdingAPI.Framework.ModLoading
                 string[] failedLabels =
                     (
                         from entry in dependencies
-                        where entry.MinVersion != null && entry.MinVersion.IsNewerThan(entry.Mod.Manifest.Version)
+                        where entry.Mod != null && entry.MinVersion != null && entry.MinVersion.IsNewerThan(entry.Mod.Manifest.Version)
                         select $"{entry.Mod.DisplayName} (needs {entry.MinVersion} or later)"
                     )
                     .ToArray();
@@ -265,11 +276,15 @@ namespace StardewModdingAPI.Framework.ModLoading
                 states[mod] = ModDependencyStatus.Checking;
 
                 // recursively sort dependencies
-                IModMetadata[] modsToLoadFirst = dependencies.Select(p => p.Mod).ToArray();
-                foreach (IModMetadata requiredMod in modsToLoadFirst)
+                foreach (var dependency in dependencies)
                 {
+                    IModMetadata requiredMod = dependency.Mod;
                     var subchain = new List<IModMetadata>(currentChain) { mod };
 
+                    // ignore missing optional dependency
+                    if (!dependency.IsRequired && requiredMod == null)
+                        continue;
+
                     // detect dependency loop
                     if (states[requiredMod] == ModDependencyStatus.Checking)
                     {
diff --git a/src/StardewModdingAPI/Framework/Models/ManifestDependency.cs b/src/StardewModdingAPI/Framework/Models/ManifestDependency.cs
index a0ff0c90..25d92a29 100644
--- a/src/StardewModdingAPI/Framework/Models/ManifestDependency.cs
+++ b/src/StardewModdingAPI/Framework/Models/ManifestDependency.cs
@@ -12,6 +12,10 @@
         /// <summary>The minimum required version (if any).</summary>
         public ISemanticVersion MinimumVersion { get; set; }
 
+#if SMAPI_2_0
+        /// <summary>Whether the dependency must be installed to use the mod.</summary>
+        public bool IsRequired { get; set; }
+#endif
 
         /*********
         ** Public methods
@@ -19,12 +23,20 @@
         /// <summary>Construct an instance.</summary>
         /// <param name="uniqueID">The unique mod ID to require.</param>
         /// <param name="minimumVersion">The minimum required version (if any).</param>
-        public ManifestDependency(string uniqueID, string minimumVersion)
+        /// <param name="required">Whether the dependency must be installed to use the mod.</param>
+        public ManifestDependency(string uniqueID, string minimumVersion
+#if SMAPI_2_0
+            , bool required = true
+#endif
+            )
         {
             this.UniqueID = uniqueID;
             this.MinimumVersion = !string.IsNullOrWhiteSpace(minimumVersion)
                 ? new SemanticVersion(minimumVersion)
                 : null;
+#if SMAPI_2_0
+            this.IsRequired = required;
+#endif
         }
     }
 }
diff --git a/src/StardewModdingAPI/Framework/Serialisation/ManifestFieldConverter.cs b/src/StardewModdingAPI/Framework/Serialisation/ManifestFieldConverter.cs
index e6d62d50..5be0f0b6 100644
--- a/src/StardewModdingAPI/Framework/Serialisation/ManifestFieldConverter.cs
+++ b/src/StardewModdingAPI/Framework/Serialisation/ManifestFieldConverter.cs
@@ -73,7 +73,12 @@ namespace StardewModdingAPI.Framework.Serialisation
                 {
                     string uniqueID = obj.Value<string>(nameof(IManifestDependency.UniqueID));
                     string minVersion = obj.Value<string>(nameof(IManifestDependency.MinimumVersion));
+#if SMAPI_2_0
+                    bool required = obj.Value<bool?>(nameof(IManifestDependency.IsRequired)) ?? true;
+                    result.Add(new ManifestDependency(uniqueID, minVersion, required));
+#else
                     result.Add(new ManifestDependency(uniqueID, minVersion));
+#endif
                 }
                 return result.ToArray();
             }