Add some nullable annotations in options system

There appeared to be one bug: if a document was opened that had a null
file path, there was a risk that we would crash because we would be
passing that around to the editor API in the legacy case.

src/EditorFeatures/Core.Wpf/Options/LegacyEditorConfigDocumentOptionsProvider.DocumentOptions.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -17,8 +19,8 @@ private class DocumentOptions : IDocumentOptions
         {
             private readonly ICodingConventionsSnapshot _codingConventionSnapshot;
             private readonly IErrorLoggerService _errorLogger;
-            private static readonly ConditionalWeakTable<IReadOnlyDictionary<string, object>, IReadOnlyDictionary<string, string>> s_convertedDictionaryCache =
-                new ConditionalWeakTable<IReadOnlyDictionary<string, object>, IReadOnlyDictionary<string, string>>();
+            private static readonly ConditionalWeakTable<IReadOnlyDictionary<string, object?>, IReadOnlyDictionary<string, string?>> s_convertedDictionaryCache =
+                new ConditionalWeakTable<IReadOnlyDictionary<string, object?>, IReadOnlyDictionary<string, string?>>();
 
             public DocumentOptions(ICodingConventionsSnapshot codingConventionSnapshot, IErrorLoggerService errorLogger)
             {
@@ -26,7 +28,7 @@ public DocumentOptions(ICodingConventionsSnapshot codingConventionSnapshot, IErr
                 _errorLogger = errorLogger;
             }
 
-            public bool TryGetDocumentOption(OptionKey option, out object value)
+            public bool TryGetDocumentOption(OptionKey option, out object? value)
             {
                 var editorConfigPersistence = option.Option.StorageLocations.OfType<IEditorConfigStorageLocation>().SingleOrDefault();
                 if (editorConfigPersistence == null)
@@ -63,33 +65,33 @@ public bool TryGetDocumentOption(OptionKey option, out object value)
             /// where we just convert the values to strings with ToString(). Ordering of the underlying dictionary is preserved, so that way
             /// code that relies on the underlying ordering of the underlying dictionary isn't affected.
             /// </summary>
-            private class StringConvertingDictionary : IReadOnlyDictionary<string, string>
+            private class StringConvertingDictionary : IReadOnlyDictionary<string, string?>
             {
-                private readonly IReadOnlyDictionary<string, object> _underlyingDictionary;
+                private readonly IReadOnlyDictionary<string, object?> _underlyingDictionary;
 
-                public StringConvertingDictionary(IReadOnlyDictionary<string, object> underlyingDictionary)
+                public StringConvertingDictionary(IReadOnlyDictionary<string, object?> underlyingDictionary)
                 {
                     _underlyingDictionary = underlyingDictionary ?? throw new ArgumentNullException(nameof(underlyingDictionary));
                 }
 
-                public string this[string key] => _underlyingDictionary[key]?.ToString();
+                public string? this[string key] => _underlyingDictionary[key]?.ToString();
 
                 public IEnumerable<string> Keys => _underlyingDictionary.Keys;
-                public IEnumerable<string> Values => _underlyingDictionary.Values.Select(s => s?.ToString());
+                public IEnumerable<string?> Values => _underlyingDictionary.Values.Select(s => s?.ToString());
 
                 public int Count => _underlyingDictionary.Count;
 
                 public bool ContainsKey(string key) => _underlyingDictionary.ContainsKey(key);
 
-                public IEnumerator<KeyValuePair<string, string>> GetEnumerator()
+                public IEnumerator<KeyValuePair<string, string?>> GetEnumerator()
                 {
                     foreach (var pair in _underlyingDictionary)
                     {
-                        yield return new KeyValuePair<string, string>(pair.Key, pair.Value?.ToString());
+                        yield return new KeyValuePair<string, string?>(pair.Key, pair.Value?.ToString());
                     }
                 }
 
-                public bool TryGetValue(string key, out string value)
+                public bool TryGetValue(string key, out string? value)
                 {
                     if (_underlyingDictionary.TryGetValue(key, out var objectValue))
                     {

src/EditorFeatures/Core.Wpf/Options/LegacyEditorConfigDocumentOptionsProvider.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
@@ -36,7 +38,7 @@ internal LegacyEditorConfigDocumentOptionsProvider(Workspace workspace, ICodingC
             _workspace = workspace;
             _listener = listenerProvider.GetListener(FeatureAttribute.Workspace);
             _codingConventionsManager = codingConventionsManager;
-            _errorLogger = workspace.Services.GetService<IErrorLoggerService>();
+            _errorLogger = workspace.Services.GetRequiredService<IErrorLoggerService>();
 
             workspace.DocumentOpened += Workspace_DocumentOpened;
             workspace.DocumentClosed += Workspace_DocumentClosed;
@@ -72,12 +74,16 @@ private void Workspace_DocumentOpened(object sender, DocumentEventArgs e)
             {
                 var documentId = e.Document.Id;
                 var filePath = e.Document.FilePath;
-                _openDocumentContexts.Add(documentId, Task.Run(async () =>
+
+                if (filePath != null)
                 {
-                    var context = await GetConventionContextAsync(filePath, CancellationToken.None).ConfigureAwait(false);
-                    OnCodingConventionContextCreated(documentId, context);
-                    return context;
-                }));
+                    _openDocumentContexts.Add(documentId, Task.Run(async () =>
+                    {
+                        var context = await GetConventionContextAsync(filePath, CancellationToken.None).ConfigureAwait(false);
+                        OnCodingConventionContextCreated(documentId, context);
+                        return context;
+                    }));
+                }
             }
         }
 
@@ -99,7 +105,7 @@ private void Workspace_WorkspaceChanged(object sender, WorkspaceChangeEventArgs
             }
         }
 
-        private void ClearOpenFileCache(ProjectId projectId = null)
+        private void ClearOpenFileCache(ProjectId? projectId = null)
         {
             lock (_gate)
             {
@@ -133,7 +139,7 @@ private void ReleaseContext_NoLock(Task<ICodingConventionContext> contextTask)
                 TaskScheduler.Default);
         }
 
-        public async Task<IDocumentOptions> GetOptionsForDocumentAsync(Document document, CancellationToken cancellationToken)
+        public async Task<IDocumentOptions?> GetOptionsForDocumentAsync(Document document, CancellationToken cancellationToken)
         {
             Task<ICodingConventionContext> contextTask;
 

src/EditorFeatures/Core.Wpf/Options/LegacyEditorConfigDocumentOptionsProviderFactory.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Composition;
 using System.IO;
@@ -32,7 +34,7 @@ class LegacyEditorConfigDocumentOptionsProviderFactory : IDocumentOptionsProvide
             _asynchronousOperationListenerProvider = asynchronousOperationListenerProvider;
         }
 
-        public IDocumentOptionsProvider TryCreate(Workspace workspace)
+        public IDocumentOptionsProvider? TryCreate(Workspace workspace)
         {
             if (EditorConfigDocumentOptionsProviderFactory.ShouldUseNativeEditorConfigSupport(workspace))
             {
@@ -84,7 +86,7 @@ private Task OnConventionFileChanged(object sender, ConventionsFileChangeEventAr
                 return ConventionFileChanged?.Invoke(this, arg) ?? Task.CompletedTask;
             }
 
-            public event ConventionsFileChangedAsyncEventHandler ConventionFileChanged;
+            public event ConventionsFileChangedAsyncEventHandler? ConventionFileChanged;
 
             public event ContextFileMovedAsyncEventHandler ContextFileMoved
             {

src/EditorFeatures/Core.Wpf/Options/LegacyEditorConfigDocumentOptionsProvider_Ide.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.CompilerServices;

src/Workspaces/Core/Portable/Options/EditorConfig/EditorConfigDocumentOptionsProviderFactory.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections.Immutable;
 using System.Composition;
@@ -18,7 +20,7 @@ public EditorConfigDocumentOptionsProviderFactory()
         {
         }
 
-        public IDocumentOptionsProvider TryCreate(Workspace workspace)
+        public IDocumentOptionsProvider? TryCreate(Workspace workspace)
         {
             if (!ShouldUseNativeEditorConfigSupport(workspace))
             {
@@ -26,7 +28,7 @@ public IDocumentOptionsProvider TryCreate(Workspace workspace)
                 return null;
             }
 
-            return new EditorConfigDocumentOptionsProvider(workspace.Services.GetService<IErrorLoggerService>());
+            return new EditorConfigDocumentOptionsProvider(workspace.Services.GetRequiredService<IErrorLoggerService>());
         }
 
         private const string LocalRegistryPath = @"Roslyn\Internal\OnOff\Features\";
@@ -49,7 +51,7 @@ public EditorConfigDocumentOptionsProvider(IErrorLoggerService errorLogger)
                 _errorLogger = errorLogger;
             }
 
-            public async Task<IDocumentOptions> GetOptionsForDocumentAsync(Document document, CancellationToken cancellationToken)
+            public async Task<IDocumentOptions?> GetOptionsForDocumentAsync(Document document, CancellationToken cancellationToken)
             {
                 var options = await document.GetAnalyzerOptionsAsync(cancellationToken).ConfigureAwait(false);
 
@@ -67,7 +69,7 @@ public DocumentOptions(ImmutableDictionary<string, string> options, IErrorLogger
                     _errorLogger = errorLogger;
                 }
 
-                public bool TryGetDocumentOption(OptionKey option, out object value)
+                public bool TryGetDocumentOption(OptionKey option, out object? value)
                 {
                     var editorConfigPersistence = option.Option.StorageLocations.OfType<IEditorConfigStorageLocation>().SingleOrDefault();
                     if (editorConfigPersistence == null)

src/Workspaces/Core/Portable/Options/IDocumentOptions.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 namespace Microsoft.CodeAnalysis.Options
 {
     /// <summary>
@@ -7,6 +9,12 @@ namespace Microsoft.CodeAnalysis.Options
     /// </summary>
     interface IDocumentOptions
     {
-        bool TryGetDocumentOption(OptionKey option, out object value);
+        /// <summary>
+        /// Attempts to fetch the value for the given option.
+        /// </summary>
+        /// <param name="option"></param>
+        /// <param name="value">The value returned. May be null even if the function returns true as "null" may be valid value for some options.</param>
+        /// <returns>True if this provider had a specific value for this option. False to indicate other providers should be queried.</returns>
+        bool TryGetDocumentOption(OptionKey option, out object? value);
     }
 }

src/Workspaces/Core/Portable/Options/IDocumentOptionsProvider.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -22,6 +26,6 @@ interface IDocumentOptionsProvider
         /// Fetches a <see cref="IDocumentOptions"/> for the given document. Any asynchronous work (looking for config files, etc.)
         /// should be done here. Can return a null-valued task to mean there is no options being provided for this document.
         /// </summary>
-        Task<IDocumentOptions> GetOptionsForDocumentAsync(Document document, CancellationToken cancellationToken);
+        Task<IDocumentOptions?> GetOptionsForDocumentAsync(Document document, CancellationToken cancellationToken);
     }
 }

src/Workspaces/Core/Portable/Options/IDocumentOptionsProviderFactory.cs

-namespace Microsoft.CodeAnalysis.Options
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+#nullable enable
+
+namespace Microsoft.CodeAnalysis.Options
 {
     /// <remarks>
     /// This interface exists so the Visual Studio workspace can create the .editorconfig provider,
@@ -8,6 +12,6 @@
     /// </remarks>
     interface IDocumentOptionsProviderFactory
     {
-        IDocumentOptionsProvider TryCreate(Workspace workspace);
+        IDocumentOptionsProvider? TryCreate(Workspace workspace);
     }
 }

src/Workspaces/Core/Portable/Options/OptionServiceFactory.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
@@ -166,14 +168,14 @@ private class DocumentSpecificOptionSet : OptionSet
             {
                 private readonly OptionSet _underlyingOptions;
                 private readonly List<IDocumentOptions> _documentOptions;
-                private ImmutableDictionary<OptionKey, object> _values;
+                private ImmutableDictionary<OptionKey, object?> _values;
 
                 public DocumentSpecificOptionSet(List<IDocumentOptions> documentOptions, OptionSet underlyingOptions)
-                    : this(documentOptions, underlyingOptions, ImmutableDictionary<OptionKey, object>.Empty)
+                    : this(documentOptions, underlyingOptions, ImmutableDictionary<OptionKey, object?>.Empty)
                 {
                 }
 
-                public DocumentSpecificOptionSet(List<IDocumentOptions> documentOptions, OptionSet underlyingOptions, ImmutableDictionary<OptionKey, object> values)
+                public DocumentSpecificOptionSet(List<IDocumentOptions> documentOptions, OptionSet underlyingOptions, ImmutableDictionary<OptionKey, object?> values)
                 {
                     _documentOptions = documentOptions;
                     _underlyingOptions = underlyingOptions;
@@ -181,7 +183,7 @@ public DocumentSpecificOptionSet(List<IDocumentOptions> documentOptions, OptionS
                 }
 
                 [PerformanceSensitive("https://github.com/dotnet/roslyn/issues/30819", AllowLocks = false)]
-                public override object GetOption(OptionKey optionKey)
+                public override object? GetOption(OptionKey optionKey)
                 {
                     // If we already know the document specific value, we're done
                     if (_values.TryGetValue(optionKey, out var value))
@@ -202,7 +204,7 @@ public override object GetOption(OptionKey optionKey)
                     return _underlyingOptions.GetOption(optionKey);
                 }
 
-                public override OptionSet WithChangedOption(OptionKey optionAndLanguage, object value)
+                public override OptionSet WithChangedOption(OptionKey optionAndLanguage, object? value)
                 {
                     return new DocumentSpecificOptionSet(_documentOptions, _underlyingOptions, _values.Add(optionAndLanguage, value));
                 }