enable nullable annotations in the rest of SMAPI core (#837)

4 files changed, 80 insertions, 65 deletions

diff --git a/src/SMAPI/Framework/ModLoading/AssemblyLoader.cs b/src/SMAPI/Framework/ModLoading/AssemblyLoader.cs
index 070ee803..72b547b1 100644
--- a/src/SMAPI/Framework/ModLoading/AssemblyLoader.cs
+++ b/src/SMAPI/Framework/ModLoading/AssemblyLoader.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.IO;
@@ -96,7 +94,12 @@ namespace StardewModdingAPI.Framework.ModLoading
             // get referenced local assemblies
             AssemblyParseResult[] assemblies;
             {
-                HashSet<string> visitedAssemblyNames = new HashSet<string>(AppDomain.CurrentDomain.GetAssemblies().Select(p => p.GetName().Name)); // don't try loading assemblies that are already loaded
+                HashSet<string> visitedAssemblyNames = new HashSet<string>( // don't try loading assemblies that are already loaded
+                    from assembly in AppDomain.CurrentDomain.GetAssemblies()
+                    let name = assembly.GetName().Name
+                    where name != null
+                    select name
+                );
                 assemblies = this.GetReferencedLocalAssemblies(new FileInfo(assemblyPath), visitedAssemblyNames, this.AssemblyDefinitionResolver).ToArray();
             }
 
@@ -113,11 +116,11 @@ namespace StardewModdingAPI.Framework.ModLoading
 
             // rewrite & load assemblies in leaf-to-root order
             bool oneAssembly = assemblies.Length == 1;
-            Assembly lastAssembly = null;
+            Assembly? lastAssembly = null;
             HashSet<string> loggedMessages = new HashSet<string>();
             foreach (AssemblyParseResult assembly in assemblies)
             {
-                if (assembly.Status == AssemblyLoadStatus.AlreadyLoaded)
+                if (!assembly.HasDefinition)
                     continue;
 
                 // rewrite assembly
@@ -165,7 +168,7 @@ namespace StardewModdingAPI.Framework.ModLoading
                 throw new IncompatibleInstructionException();
 
             // last assembly loaded is the root
-            return lastAssembly;
+            return lastAssembly!;
         }
 
         /// <summary>Get whether an assembly is loaded.</summary>
@@ -174,7 +177,8 @@ namespace StardewModdingAPI.Framework.ModLoading
         {
             try
             {
-                return this.AssemblyDefinitionResolver.Resolve(reference) != null;
+                _ = this.AssemblyDefinitionResolver.Resolve(reference);
+                return true;
             }
             catch (AssemblyResolutionException)
             {
@@ -190,7 +194,7 @@ namespace StardewModdingAPI.Framework.ModLoading
         /// assemblies (especially with Mono). Since this is meant to be called on <see cref="AppDomain.AssemblyResolve"/>,
         /// the implicit assumption is that loading the exact assembly failed.
         /// </remarks>
-        public static Assembly ResolveAssembly(string name)
+        public static Assembly? ResolveAssembly(string name)
         {
             string shortName = name.Split(new[] { ',' }, 2).First(); // get simple name (without version and culture)
             return AppDomain.CurrentDomain
@@ -212,7 +216,8 @@ namespace StardewModdingAPI.Framework.ModLoading
         /// <summary>Track an object for disposal as part of the assembly loader.</summary>
         /// <typeparam name="T">The instance type.</typeparam>
         /// <param name="instance">The disposable instance.</param>
-        private T TrackForDisposal<T>(T instance) where T : IDisposable
+        private T TrackForDisposal<T>(T instance)
+            where T : IDisposable
         {
             this.Disposables.Add(instance);
             return instance;
@@ -321,9 +326,9 @@ namespace StardewModdingAPI.Framework.ModLoading
                     // rewrite types using custom attributes
                     foreach (TypeDefinition type in module.GetTypes())
                     {
-                        foreach (var attr in type.CustomAttributes)
+                        foreach (CustomAttribute attr in type.CustomAttributes)
                         {
-                            foreach (var conField in attr.ConstructorArguments)
+                            foreach (CustomAttributeArgument conField in attr.ConstructorArguments)
                             {
                                 if (conField.Value is TypeReference typeRef)
                                     this.ChangeTypeScope(typeRef);
@@ -382,7 +387,7 @@ namespace StardewModdingAPI.Framework.ModLoading
         {
             // get message template
             // ($phrase is replaced with the noun phrase or messages)
-            string template = null;
+            string? template = null;
             switch (result)
             {
                 case InstructionHandleResult.Rewritten:
@@ -441,20 +446,20 @@ namespace StardewModdingAPI.Framework.ModLoading
             // format messages
             string phrase = handler.Phrases.Any()
                 ? string.Join(", ", handler.Phrases)
-                : handler.DefaultPhrase ?? handler.GetType().Name;
+                : handler.DefaultPhrase;
             this.Monitor.LogOnce(loggedMessages, template.Replace("$phrase", phrase));
         }
 
         /// <summary>Get the correct reference to use for compatibility with the current platform.</summary>
         /// <param name="type">The type reference to rewrite.</param>
-        private void ChangeTypeScope(TypeReference type)
+        private void ChangeTypeScope(TypeReference? type)
         {
             // check skip conditions
             if (type == null || type.FullName.StartsWith("System."))
                 return;
 
             // get assembly
-            if (!this.TypeAssemblies.TryGetValue(type.FullName, out Assembly assembly))
+            if (!this.TypeAssemblies.TryGetValue(type.FullName, out Assembly? assembly))
                 return;
 
             // replace scope
diff --git a/src/SMAPI/Framework/ModLoading/AssemblyParseResult.cs b/src/SMAPI/Framework/ModLoading/AssemblyParseResult.cs
index 56bd5a8b..b133f8d6 100644
--- a/src/SMAPI/Framework/ModLoading/AssemblyParseResult.cs
+++ b/src/SMAPI/Framework/ModLoading/AssemblyParseResult.cs
@@ -1,5 +1,5 @@
-#nullable disable
-
+using System;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using Mono.Cecil;
 
@@ -15,11 +15,15 @@ namespace StardewModdingAPI.Framework.ModLoading
         public readonly FileInfo File;
 
         /// <summary>The assembly definition.</summary>
-        public readonly AssemblyDefinition Definition;
+        public readonly AssemblyDefinition? Definition;
 
         /// <summary>The result of the assembly load.</summary>
         public AssemblyLoadStatus Status;
 
+        /// <summary>Whether the <see cref="Definition"/> is loaded and ready (i.e. the <see cref="Status"/> is not <see cref="AssemblyLoadStatus.AlreadyLoaded"/> or <see cref="AssemblyLoadStatus.Failed"/>).</summary>
+        [MemberNotNullWhen(true, nameof(AssemblyParseResult.Definition))]
+        public bool HasDefinition => this.Status == AssemblyLoadStatus.Okay;
+
 
         /*********
         ** Public methods
@@ -28,11 +32,14 @@ namespace StardewModdingAPI.Framework.ModLoading
         /// <param name="file">The original assembly file.</param>
         /// <param name="assembly">The assembly definition.</param>
         /// <param name="status">The result of the assembly load.</param>
-        public AssemblyParseResult(FileInfo file, AssemblyDefinition assembly, AssemblyLoadStatus status)
+        public AssemblyParseResult(FileInfo file, AssemblyDefinition? assembly, AssemblyLoadStatus status)
         {
             this.File = file;
             this.Definition = assembly;
             this.Status = status;
+
+            if (status == AssemblyLoadStatus.Okay && assembly == null)
+                throw new InvalidOperationException($"Invalid assembly parse result: load status {status} with a null assembly.");
         }
     }
 }
diff --git a/src/SMAPI/Framework/ModLoading/ModResolver.cs b/src/SMAPI/Framework/ModLoading/ModResolver.cs
index 4fdeefbc..afb388d0 100644
--- a/src/SMAPI/Framework/ModLoading/ModResolver.cs
+++ b/src/SMAPI/Framework/ModLoading/ModResolver.cs
@@ -1,7 +1,6 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using StardewModdingAPI.Toolkit;
@@ -28,10 +27,10 @@ namespace StardewModdingAPI.Framework.ModLoading
         {
             foreach (ModFolder folder in toolkit.GetModFolders(rootPath))
             {
-                Manifest manifest = folder.Manifest;
+                Manifest? manifest = folder.Manifest;
 
                 // parse internal data record (if any)
-                ModDataRecordVersionedFields dataRecord = modDatabase.Get(manifest?.UniqueID)?.GetVersionedFields(manifest);
+                ModDataRecordVersionedFields? dataRecord = modDatabase.Get(manifest?.UniqueID)?.GetVersionedFields(manifest);
 
                 // apply defaults
                 if (manifest != null && dataRecord?.UpdateKey is not null)
@@ -43,7 +42,7 @@ namespace StardewModdingAPI.Framework.ModLoading
                     ? ModMetadataStatus.Found
                     : ModMetadataStatus.Failed;
 
-                var metadata = new ModMetadata(folder.DisplayName, folder.Directory.FullName, rootPath, manifest, dataRecord, isIgnored: shouldIgnore);
+                IModMetadata metadata = new ModMetadata(folder.DisplayName, folder.Directory.FullName, rootPath, manifest, dataRecord, isIgnored: shouldIgnore);
                 if (shouldIgnore)
                     metadata.SetStatus(status, ModFailReason.DisabledByDotConvention, "disabled by dot convention");
                 else
@@ -57,7 +56,9 @@ namespace StardewModdingAPI.Framework.ModLoading
         /// <param name="mods">The mod manifests to validate.</param>
         /// <param name="apiVersion">The current SMAPI version.</param>
         /// <param name="getUpdateUrl">Get an update URL for an update key (if valid).</param>
-        public void ValidateManifests(IEnumerable<IModMetadata> mods, ISemanticVersion apiVersion, Func<string, string> getUpdateUrl)
+        [SuppressMessage("ReSharper", "ConstantConditionalAccessQualifier", Justification = "Manifest values may be null before they're validated.")]
+        [SuppressMessage("ReSharper", "ConditionIsAlwaysTrueOrFalse", Justification = "Manifest values may be null before they're validated.")]
+        public void ValidateManifests(IEnumerable<IModMetadata> mods, ISemanticVersion apiVersion, Func<string, string?> getUpdateUrl)
         {
             mods = mods.ToArray();
 
@@ -84,7 +85,7 @@ namespace StardewModdingAPI.Framework.ModLoading
                             List<string> updateUrls = new List<string>();
                             foreach (UpdateKey key in mod.GetUpdateKeys(validOnly: true))
                             {
-                                string url = getUpdateUrl(key.ToString());
+                                string? url = getUpdateUrl(key.ToString());
                                 if (url != null)
                                     updateUrls.Add(url);
                             }
@@ -94,7 +95,7 @@ namespace StardewModdingAPI.Framework.ModLoading
 
                             // build error
                             string error = $"{reasonPhrase}. Please check for a ";
-                            if (mod.DataRecord.StatusUpperVersion == null || mod.Manifest.Version.Equals(mod.DataRecord.StatusUpperVersion))
+                            if (mod.DataRecord.StatusUpperVersion == null || mod.Manifest.Version?.Equals(mod.DataRecord.StatusUpperVersion) == true)
                                 error += "newer version";
                             else
                                 error += $"version newer than {mod.DataRecord.StatusUpperVersion}";
@@ -133,21 +134,21 @@ namespace StardewModdingAPI.Framework.ModLoading
                     if (hasDll)
                     {
                         // invalid filename format
-                        if (mod.Manifest.EntryDll.Intersect(Path.GetInvalidFileNameChars()).Any())
+                        if (mod.Manifest.EntryDll!.Intersect(Path.GetInvalidFileNameChars()).Any())
                         {
                             mod.SetStatus(ModMetadataStatus.Failed, ModFailReason.InvalidManifest, $"its manifest has invalid filename '{mod.Manifest.EntryDll}' for the EntryDLL field.");
                             continue;
                         }
 
                         // invalid path
-                        if (!File.Exists(Path.Combine(mod.DirectoryPath, mod.Manifest.EntryDll)))
+                        if (!File.Exists(Path.Combine(mod.DirectoryPath, mod.Manifest.EntryDll!)))
                         {
                             mod.SetStatus(ModMetadataStatus.Failed, ModFailReason.InvalidManifest, $"its DLL '{mod.Manifest.EntryDll}' doesn't exist.");
                             continue;
                         }
 
                         // invalid capitalization
-                        string actualFilename = new DirectoryInfo(mod.DirectoryPath).GetFiles(mod.Manifest.EntryDll).FirstOrDefault()?.Name;
+                        string? actualFilename = new DirectoryInfo(mod.DirectoryPath).GetFiles(mod.Manifest.EntryDll!).FirstOrDefault()?.Name;
                         if (actualFilename != mod.Manifest.EntryDll)
                         {
                             mod.SetStatus(ModMetadataStatus.Failed, ModFailReason.InvalidManifest, $"its {nameof(IManifest.EntryDll)} value '{mod.Manifest.EntryDll}' doesn't match the actual file capitalization '{actualFilename}'. The capitalization must match for crossplatform compatibility.");
@@ -159,7 +160,7 @@ namespace StardewModdingAPI.Framework.ModLoading
                     else
                     {
                         // invalid content pack ID
-                        if (string.IsNullOrWhiteSpace(mod.Manifest.ContentPackFor.UniqueID))
+                        if (string.IsNullOrWhiteSpace(mod.Manifest.ContentPackFor!.UniqueID))
                         {
                             mod.SetStatus(ModMetadataStatus.Failed, ModFailReason.InvalidManifest, $"its manifest declares {nameof(IManifest.ContentPackFor)} without its required {nameof(IManifestContentPackFor.UniqueID)} field.");
                             continue;
@@ -190,7 +191,7 @@ namespace StardewModdingAPI.Framework.ModLoading
                     mod.SetStatus(ModMetadataStatus.Failed, ModFailReason.InvalidManifest, "its manifest specifies an invalid ID (IDs must only contain letters, numbers, underscores, periods, or hyphens).");
 
                 // validate dependencies
-                foreach (var dependency in mod.Manifest.Dependencies)
+                foreach (IManifestDependency? dependency in mod.Manifest.Dependencies)
                 {
                     // null dependency
                     if (dependency == null)
@@ -328,8 +329,11 @@ namespace StardewModdingAPI.Framework.ModLoading
                 string[] failedLabels =
                     (
                         from entry in dependencies
-                        where entry.Mod != null && entry.MinVersion != null && entry.MinVersion.IsNewerThan(entry.Mod.Manifest.Version)
-                        select $"{entry.Mod.DisplayName} (needs {entry.MinVersion} or later)"
+                        where
+                            entry.Mod != null
+                            && entry.MinVersion != null
+                            && entry.MinVersion.IsNewerThan(entry.Mod.Manifest.Version)
+                        select $"{entry.Mod!.DisplayName} (needs {entry.MinVersion} or later)"
                     )
                     .ToArray();
                 if (failedLabels.Any())
@@ -345,16 +349,14 @@ namespace StardewModdingAPI.Framework.ModLoading
                 states[mod] = ModDependencyStatus.Checking;
 
                 // recursively sort dependencies
-                foreach (var dependency in dependencies)
+                foreach (ModDependency dependency in dependencies)
                 {
-                    IModMetadata requiredMod = dependency.Mod;
-                    var subchain = new List<IModMetadata>(currentChain) { mod };
-
-                    // ignore missing optional dependency
-                    if (!dependency.IsRequired && requiredMod == null)
-                        continue;
+                    IModMetadata? requiredMod = dependency.Mod;
+                    if (requiredMod == null)
+                        continue; // missing dependencies are handled earlier
 
                     // detect dependency loop
+                    var subchain = new List<IModMetadata>(currentChain) { mod };
                     if (states[requiredMod] == ModDependencyStatus.Checking)
                     {
                         sortedMods.Push(mod);
@@ -363,8 +365,8 @@ namespace StardewModdingAPI.Framework.ModLoading
                     }
 
                     // recursively process each dependency
-                    var substatus = this.ProcessDependencies(mods, modDatabase, requiredMod, states, sortedMods, subchain);
-                    switch (substatus)
+                    var subStatus = this.ProcessDependencies(mods, modDatabase, requiredMod, states, sortedMods, subchain);
+                    switch (subStatus)
                     {
                         // sorted successfully
                         case ModDependencyStatus.Sorted:
@@ -380,7 +382,7 @@ namespace StardewModdingAPI.Framework.ModLoading
                         // unexpected status
                         case ModDependencyStatus.Queued:
                         case ModDependencyStatus.Checking:
-                            throw new InvalidModStateException($"Something went wrong sorting dependencies: mod '{requiredMod.DisplayName}' unexpectedly stayed in the '{substatus}' status.");
+                            throw new InvalidModStateException($"Something went wrong sorting dependencies: mod '{requiredMod.DisplayName}' unexpectedly stayed in the '{subStatus}' status.");
 
                         // sanity check
                         default:
@@ -399,14 +401,11 @@ namespace StardewModdingAPI.Framework.ModLoading
         /// <param name="loadedMods">The loaded mods.</param>
         private IEnumerable<ModDependency> GetDependenciesFrom(IManifest manifest, IModMetadata[] loadedMods)
         {
-            IModMetadata FindMod(string id) => loadedMods.FirstOrDefault(m => m.HasID(id));
+            IModMetadata? FindMod(string id) => loadedMods.FirstOrDefault(m => m.HasID(id));
 
             // yield dependencies
-            if (manifest.Dependencies != null)
-            {
-                foreach (var entry in manifest.Dependencies)
-                    yield return new ModDependency(entry.UniqueID, entry.MinimumVersion, FindMod(entry.UniqueID), entry.IsRequired);
-            }
+            foreach (IManifestDependency entry in manifest.Dependencies)
+                yield return new ModDependency(entry.UniqueID, entry.MinimumVersion, FindMod(entry.UniqueID), entry.IsRequired);
 
             // yield content pack parent
             if (manifest.ContentPackFor != null)
@@ -415,10 +414,10 @@ namespace StardewModdingAPI.Framework.ModLoading
 
         /// <summary>Get a technical message indicating why a mod's compatibility status was overridden, if applicable.</summary>
         /// <param name="mod">The mod metadata.</param>
-        private string GetTechnicalReasonForStatusOverride(IModMetadata mod)
+        private string? GetTechnicalReasonForStatusOverride(IModMetadata mod)
         {
             // get compatibility list record
-            var data = mod.DataRecord;
+            ModDataRecordVersionedFields? data = mod.DataRecord;
             if (data == null)
                 return null;
 
@@ -432,14 +431,14 @@ namespace StardewModdingAPI.Framework.ModLoading
             };
 
             // get reason
-            string[] reasons = new[] { mod.DataRecord.StatusReasonPhrase, mod.DataRecord.StatusReasonDetails }
+            string?[] reasons = new[] { data.StatusReasonPhrase, data.StatusReasonDetails }
                 .Where(p => !string.IsNullOrWhiteSpace(p))
                 .ToArray();
 
             // build message
             return
                 $"marked {statusLabel} in SMAPI's internal compatibility list for "
-                + (mod.DataRecord.StatusUpperVersion != null ? $"versions up to {mod.DataRecord.StatusUpperVersion}" : "all versions")
+                + (data.StatusUpperVersion != null ? $"versions up to {data.StatusUpperVersion}" : "all versions")
                 + ": "
                 + (reasons.Any() ? string.Join(": ", reasons) : "no reason given")
                 + ".";
@@ -459,13 +458,13 @@ namespace StardewModdingAPI.Framework.ModLoading
             public string ID { get; }
 
             /// <summary>The minimum required version (if any).</summary>
-            public ISemanticVersion MinVersion { get; }
+            public ISemanticVersion? MinVersion { get; }
 
             /// <summary>Whether the mod shouldn't be loaded if the dependency isn't available.</summary>
             public bool IsRequired { get; }
 
             /// <summary>The loaded mod that fulfills the dependency (if available).</summary>
-            public IModMetadata Mod { get; }
+            public IModMetadata? Mod { get; }
 
 
             /*********
@@ -476,7 +475,7 @@ namespace StardewModdingAPI.Framework.ModLoading
             /// <param name="minVersion">The minimum required version (if any).</param>
             /// <param name="mod">The loaded mod that fulfills the dependency (if available).</param>
             /// <param name="isRequired">Whether the mod shouldn't be loaded if the dependency isn't available.</param>
-            public ModDependency(string id, ISemanticVersion minVersion, IModMetadata mod, bool isRequired)
+            public ModDependency(string id, ISemanticVersion? minVersion, IModMetadata? mod, bool isRequired)
             {
                 this.ID = id;
                 this.MinVersion = minVersion;
diff --git a/src/SMAPI/Framework/ModLoading/Rewriters/FieldReplaceRewriter.cs b/src/SMAPI/Framework/ModLoading/Rewriters/FieldReplaceRewriter.cs
index 806fca62..d5f4cf4a 100644
--- a/src/SMAPI/Framework/ModLoading/Rewriters/FieldReplaceRewriter.cs
+++ b/src/SMAPI/Framework/ModLoading/Rewriters/FieldReplaceRewriter.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.Reflection;
@@ -33,13 +31,19 @@ namespace StardewModdingAPI.Framework.ModLoading.Rewriters
         /// <param name="toFieldName">The new field name to reference.</param>
         public FieldReplaceRewriter AddField(Type fromType, string fromFieldName, Type toType, string toFieldName)
         {
+            // validate parameters
+            if (fromType == null)
+                throw new InvalidOperationException("Can't replace a field on a null source type.");
+            if (toType == null)
+                throw new InvalidOperationException("Can't replace a field on a null target type.");
+
             // get full type name
-            string fromTypeName = fromType?.FullName;
+            string? fromTypeName = fromType.FullName;
             if (fromTypeName == null)
                 throw new InvalidOperationException($"Can't replace field for invalid type reference {toType}.");
 
             // get target field
-            FieldInfo toField = toType.GetField(toFieldName);
+            FieldInfo? toField = toType.GetField(toFieldName);
             if (toField == null)
                 throw new InvalidOperationException($"The {toType.FullName} class doesn't have a {toFieldName} field.");
 
@@ -54,15 +58,15 @@ namespace StardewModdingAPI.Framework.ModLoading.Rewriters
         /// <inheritdoc />
         public override bool Handle(ModuleDefinition module, ILProcessor cil, Instruction instruction)
         {
-            FieldReference fieldRef = RewriteHelper.AsFieldReference(instruction);
-            string declaringType = fieldRef?.DeclaringType?.FullName;
+            FieldReference? fieldRef = RewriteHelper.AsFieldReference(instruction);
+            string? declaringType = fieldRef?.DeclaringType?.FullName;
 
             // get mapped field
-            if (declaringType == null || !this.FieldMaps.TryGetValue(declaringType, out var fieldMap) || !fieldMap.TryGetValue(fieldRef.Name, out FieldInfo toField))
+            if (declaringType == null || !this.FieldMaps.TryGetValue(declaringType, out var fieldMap) || !fieldMap.TryGetValue(fieldRef!.Name, out FieldInfo? toField))
                 return false;
 
             // replace with new field
-            this.Phrases.Add($"{fieldRef.DeclaringType.Name}.{fieldRef.Name} field");
+            this.Phrases.Add($"{fieldRef.DeclaringType!.Name}.{fieldRef.Name} field");
             instruction.Operand = module.ImportReference(toField);
             return this.MarkRewritten();
         }