Enable nullable reference types

Closes #36

src/.editorconfig

@@ -77,4 +77,7 @@ dotnet_diagnostic.CA1032.severity = none
 dotnet_diagnostic.CA1826.severity = none
 
 # RCS1079: Throwing of new NotImplementedException.
-dotnet_diagnostic.RCS1079.severity = warning
+dotnet_diagnostic.RCS1079.severity = warning
+
+# RCS1057: Add empty line between declarations.
+dotnet_diagnostic.RCS1057.severity = none

src/Directory.Build.props

@@ -34,7 +34,7 @@
   <ItemGroup Label="Package References">
     <PackageReference Include="MinVer" PrivateAssets="All" Version="2.3.0" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" PrivateAssets="All" Version="1.0.0" />
-    <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.9.8">
+    <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="3.3.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>

src/Spectre.Console.Tests/Spectre.Console.Tests.csproj

@@ -7,11 +7,13 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.5.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.7.0" />
     <PackageReference Include="Shouldly" Version="4.0.0-beta0002" />
-    <PackageReference Include="xunit" Version="2.4.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
-    <PackageReference Include="coverlet.collector" Version="1.2.0" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
   </ItemGroup>
 
   <ItemGroup>

src/Spectre.Console/AnsiConsoleSettings.cs

@@ -21,6 +21,6 @@ namespace Spectre.Console
         /// <summary>
         /// Gets or sets the out buffer.
         /// </summary>
-        public TextWriter Out { get; set; }
+        public TextWriter? Out { get; set; }
     }
 }

src/Spectre.Console/Capabilities.cs

@@ -50,7 +50,7 @@ namespace Spectre.Console
                 ColorSystem.Standard => "4 bits",
                 ColorSystem.EightBit => "8 bits",
                 ColorSystem.TrueColor => "24 bits",
-                _ => "?"
+                _ => "?",
             };
 
             return $"ANSI={supportsAnsi}, Colors={ColorSystem}, Kind={legacyConsole} ({bits})";

src/Spectre.Console/Color.cs

@@ -74,7 +74,7 @@ namespace Spectre.Console
         }
 
         /// <inheritdoc/>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is Color color && Equals(color);
         }

src/Spectre.Console/Composition/Border.cs

@@ -57,15 +57,20 @@ namespace Spectre.Console.Composition
         private Dictionary<BorderPart, string> Initialize()
         {
             var lookup = new Dictionary<BorderPart, string>();
-            foreach (BorderPart part in Enum.GetValues(typeof(BorderPart)))
+            foreach (BorderPart? part in Enum.GetValues(typeof(BorderPart)))
             {
-                var text = GetBoxPart(part);
+                if (part == null)
+                {
+                    continue;
+                }
+
+                var text = GetBoxPart(part.Value);
                 if (text.Length > 1)
                 {
                     throw new InvalidOperationException("A box part cannot contain more than one character.");
                 }
 
-                lookup.Add(part, GetBoxPart(part));
+                lookup.Add(part.Value, GetBoxPart(part.Value));
             }
 
             return lookup;

src/Spectre.Console/Composition/GridColumn.cs

@@ -9,22 +9,22 @@ namespace Spectre.Console
         /// Gets or sets the width of the column.
         /// If <c>null</c>, the column will adapt to it's contents.
         /// </summary>
-        public int? Width { get; set; } = null;
+        public int? Width { get; set; }
 
         /// <summary>
         /// Gets or sets a value indicating whether wrapping of
         /// text within the column should be prevented.
         /// </summary>
-        public bool NoWrap { get; set; } = false;
+        public bool NoWrap { get; set; }
 
         /// <summary>
         /// Gets or sets the padding of the column.
         /// </summary>
-        public Padding? Padding { get; set; } = null;
+        public Padding? Padding { get; set; }
 
         /// <summary>
         /// Gets or sets the alignment of the column.
         /// </summary>
-        public Justify? Alignment { get; set; } = null;
+        public Justify? Alignment { get; set; }
     }
 }

src/Spectre.Console/Composition/Justify.cs

@@ -16,7 +16,7 @@ namespace Spectre.Console
         Right = 1,
 
         /// <summary>
-        /// Centered
+        /// Centered.
         /// </summary>
         Center = 2,
     }

src/Spectre.Console/Composition/Measurement.cs

@@ -29,7 +29,7 @@ namespace Spectre.Console.Composition
         }
 
         /// <inheritdoc/>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is Measurement measurement && Equals(measurement);
         }

src/Spectre.Console/Composition/Padding.cs

@@ -29,7 +29,7 @@ namespace Spectre.Console
         }
 
         /// <inheritdoc/>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is Padding padding && Equals(padding);
         }

src/Spectre.Console/Composition/Panel.cs

@@ -9,6 +9,8 @@ namespace Spectre.Console
     /// </summary>
     public sealed class Panel : IRenderable
     {
+        private const int EdgeWidth = 2;
+
         private readonly IRenderable _child;
 
         /// <summary>
@@ -26,14 +28,14 @@ namespace Spectre.Console
         /// <summary>
         /// Gets or sets the alignment of the panel contents.
         /// </summary>
-        public Justify? Alignment { get; set; } = null;
+        public Justify? Alignment { get; set; }
 
         /// <summary>
         /// Gets or sets a value indicating whether or not the panel should
         /// fit the available space. If <c>false</c>, the panel width will be
         /// auto calculated. Defaults to <c>false</c>.
         /// </summary>
-        public bool Expand { get; set; } = false;
+        public bool Expand { get; set; }
 
         /// <summary>
         /// Gets or sets the padding.
@@ -61,13 +63,12 @@ namespace Spectre.Console
         {
             var border = Composition.Border.GetBorder(Border, (context.LegacyConsole || !context.Unicode) && SafeBorder);
 
-            var edgeWidth = 2;
             var paddingWidth = Padding.GetHorizontalPadding();
-            var childWidth = width - edgeWidth - paddingWidth;
+            var childWidth = width - EdgeWidth - paddingWidth;
 
             if (!Expand)
             {
-                var measurement = _child.Measure(context, width - edgeWidth - paddingWidth);
+                var measurement = _child.Measure(context, width - EdgeWidth - paddingWidth);
                 childWidth = measurement.Max;
             }
 

src/Spectre.Console/Composition/Segment.cs

@@ -50,7 +50,12 @@ namespace Spectre.Console.Composition
 
         private Segment(string text, Style style, bool lineBreak)
         {
-            Text = text?.NormalizeLineEndings() ?? throw new ArgumentNullException(nameof(text));
+            if (text is null)
+            {
+                throw new ArgumentNullException(nameof(text));
+            }
+
+            Text = text.NormalizeLineEndings();
             Style = style;
             IsLineBreak = lineBreak;
         }
@@ -89,7 +94,7 @@ namespace Spectre.Console.Composition
         /// </summary>
         /// <param name="offset">The offset where to split the segment.</param>
         /// <returns>One or two new segments representing the split.</returns>
-        public (Segment First, Segment Second) Split(int offset)
+        public (Segment First, Segment? Second) Split(int offset)
         {
             if (offset < 0)
             {

src/Spectre.Console/Composition/Table.Calculations.cs

@@ -11,6 +11,8 @@ namespace Spectre.Console
     /// </summary>
     public sealed partial class Table
     {
+        private const int EdgeCount = 2;
+
         // Calculate the widths of each column, including padding, not including borders.
         // Ported from Rich by Will McGugan, licensed under MIT.
         // https://github.com/willmcgugan/rich/blob/527475837ebbfc427530b3ee0d4d0741d2d0fc6d/rich/table.py#L394
@@ -115,10 +117,9 @@ namespace Spectre.Console
 
         private int GetExtraWidth(bool includePadding)
         {
-            var edges = 2;
             var separators = _columns.Count - 1;
             var padding = includePadding ? _columns.Select(x => x.Padding.GetHorizontalPadding()).Sum() : 0;
-            return separators + edges + padding;
+            return separators + EdgeCount + padding;
         }
     }
 }

src/Spectre.Console/Composition/Table.cs

@@ -39,12 +39,12 @@ namespace Spectre.Console
         /// fit the available space. If <c>false</c>, the table width will be
         /// auto calculated. Defaults to <c>false</c>.
         /// </summary>
-        public bool Expand { get; set; } = false;
+        public bool Expand { get; set; }
 
         /// <summary>
         /// Gets or sets the width of the table.
         /// </summary>
-        public int? Width { get; set; } = null;
+        public int? Width { get; set; }
 
         /// <summary>
         /// Gets or sets a value indicating whether or not to use
@@ -54,7 +54,7 @@ namespace Spectre.Console
         public bool SafeBorder { get; set; } = true;
 
         // Whether this is a grid or not.
-        internal bool IsGrid { get; set; } = false;
+        internal bool IsGrid { get; set; }
 
         // Whether or not the most right cell should be padded.
         // This is almost always the case, unless we're rendering

src/Spectre.Console/Composition/Text.cs

@@ -201,7 +201,7 @@ namespace Spectre.Console
             return result;
         }
 
-        private IEnumerable<Segment> SplitLineBreaks(IEnumerable<Segment> segments)
+        private static IEnumerable<Segment> SplitLineBreaks(IEnumerable<Segment> segments)
         {
             // Creates individual segments of line breaks.
             var result = new List<Segment>();
@@ -228,7 +228,11 @@ namespace Spectre.Console
                     }
 
                     result.Add(Segment.LineBreak());
-                    queue.Push(new Segment(second.Text.Substring(1), second.Style));
+
+                    if (second != null)
+                    {
+                        queue.Push(new Segment(second.Text.Substring(1), second.Style));
+                    }
                 }
             }
 

src/Spectre.Console/Internal/Colors/ColorTable.cs

@@ -45,7 +45,7 @@ namespace Spectre.Console.Internal
             return ColorPalette.EightBit[number];
         }
 
-        public static string GetName(int number)
+        public static string? GetName(int number)
         {
             _nameLookup.TryGetValue(number, out var name);
             return name;

src/Spectre.Console/Internal/Extensions/StringExtensions.cs

@@ -17,14 +17,9 @@ namespace Spectre.Console.Internal
 
         public static string NormalizeLineEndings(this string text, bool native = false)
         {
-            if (text == null)
-            {
-                return null;
-            }
-
-            var normalized = text?.Replace("\r\n", "\n")
-                ?.Replace("\r", string.Empty);
+            text ??= string.Empty;
 
+            var normalized = text?.Replace("\r\n", "\n")?.Replace("\r", string.Empty) ?? string.Empty;
             if (native && !_alreadyNormalized)
             {
                 normalized = normalized.Replace("\n", Environment.NewLine);
@@ -35,7 +30,8 @@ namespace Spectre.Console.Internal
 
         public static string[] SplitLines(this string text)
         {
-            return text.NormalizeLineEndings().Split(new[] { '\n' }, StringSplitOptions.None);
+            var result = text?.NormalizeLineEndings()?.Split(new[] { '\n' }, StringSplitOptions.None);
+            return result ?? Array.Empty<string>();
         }
     }
 }

src/Spectre.Console/Internal/Text/Markup/MarkupParser.cs

@@ -6,7 +6,7 @@ namespace Spectre.Console.Internal
 {
     internal static class MarkupParser
     {
-        public static Text Parse(string text, Style style = null)
+        public static Text Parse(string text, Style? style = null)
         {
             style ??= Style.Plain;
 
@@ -18,6 +18,10 @@ namespace Spectre.Console.Internal
             while (tokenizer.MoveNext())
             {
                 var token = tokenizer.Current;
+                if (token == null)
+                {
+                    break;
+                }
 
                 if (token.Kind == MarkupTokenKind.Open)
                 {

src/Spectre.Console/Internal/Text/Markup/MarkupTokenizer.cs

@@ -7,7 +7,7 @@ namespace Spectre.Console.Internal
     {
         private readonly StringBuffer _reader;
 
-        public MarkupToken Current { get; private set; }
+        public MarkupToken? Current { get; private set; }
 
         public MarkupTokenizer(string text)
         {

src/Spectre.Console/Internal/Text/StringBuffer.cs

@@ -1,10 +1,12 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 
 namespace Spectre.Console.Internal
 {
     internal sealed class StringBuffer : IDisposable
     {
+        [SuppressMessage("Usage", "CA2213:Disposable fields should be disposed", Justification = "False positive")]
         private readonly StringReader _reader;
         private readonly int _length;
 

src/Spectre.Console/Internal/Text/StyleParser.cs

@@ -14,16 +14,23 @@ namespace Spectre.Console.Internal
                 throw new InvalidOperationException(error);
             }
 
+            if (style == null)
+            {
+                // This should not happen, but we need to please the compiler
+                // which cannot know that style isn't null here.
+                throw new InvalidOperationException("Could not parse style.");
+            }
+
             return style;
         }
 
-        public static bool TryParse(string text, out Style style)
+        public static bool TryParse(string text, out Style? style)
         {
             style = Parse(text, out var error);
             return error == null;
         }
 
-        private static Style Parse(string text, out string error)
+        private static Style? Parse(string text, out string? error)
         {
             var effectiveDecoration = (Decoration?)null;
             var effectiveForeground = (Color?)null;
@@ -113,11 +120,11 @@ namespace Spectre.Console.Internal
         }
 
         [SuppressMessage("Design", "CA1031:Do not catch general exception types")]
-        private static Color? ParseHexColor(string hex, out string error)
+        private static Color? ParseHexColor(string hex, out string? error)
         {
             error = null;
 
-            hex = hex ?? string.Empty;
+            hex ??= string.Empty;
             hex = hex.Replace("#", string.Empty).Trim();
 
             try
@@ -151,11 +158,12 @@ namespace Spectre.Console.Internal
         }
 
         [SuppressMessage("Design", "CA1031:Do not catch general exception types")]
-        private static Color? ParseRgbColor(string rgb, out string error)
+        private static Color? ParseRgbColor(string rgb, out string? error)
         {
             try
             {
                 error = null;
+
                 var normalized = rgb ?? string.Empty;
                 if (normalized.Length >= 3)
                 {

src/Spectre.Console/Internal/Utilities/Ratio.cs

@@ -40,7 +40,7 @@ namespace Spectre.Console.Internal
             return result;
         }
 
-        public static List<int> Distribute(int total, List<int> ratios, List<int> minimums = null)
+        public static List<int> Distribute(int total, List<int> ratios, List<int>? minimums = null)
         {
             if (minimums != null)
             {

src/Spectre.Console/Spectre.Console.csproj

@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
@@ -9,27 +10,21 @@
     <None Include="../../gfx/small-logo.png" Pack="true" PackagePath="\" Link="Properties/small-logo.png" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Compile Update="**/ColorPalette.*.cs">
-      <DependentUpon>**/ColorPalette.cs</DependentUpon>
-    </Compile>
-    <Compile Update="Color.*.cs">
-      <DependentUpon>Color.cs</DependentUpon>
-    </Compile>
-    <Compile Update="AnsiConsole.*.cs">
-      <DependentUpon>AnsiConsole.cs</DependentUpon>
-    </Compile>
-    <Compile Update="ConsoleExtensions.*.cs">
-      <DependentUpon>ConsoleExtensions.cs</DependentUpon>
-    </Compile>
-    <Compile Update="**/Table.*.cs">
-      <DependentUpon>**/Table.cs</DependentUpon>
-    </Compile>
-
-  </ItemGroup>
-
   <ItemGroup>
     <PackageReference Include="System.Memory" Version="4.5.4" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="TunnelVisionLabs.ReferenceAssemblyAnnotator" Version="1.0.0-alpha.160" PrivateAssets="all" />
+    <PackageDownload Include="Microsoft.NETCore.App.Ref" Version="[$(AnnotatedReferenceAssemblyVersion)]" />
+    <PackageReference Include="Nullable" Version="1.2.1">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+  <PropertyGroup>
+    <AnnotatedReferenceAssemblyVersion>3.0.0</AnnotatedReferenceAssemblyVersion>
+    <GenerateNullableAttributes>False</GenerateNullableAttributes>
+  </PropertyGroup>
+
 </Project>

src/Spectre.Console/Style.cs

@@ -67,7 +67,7 @@ namespace Spectre.Console
         /// if the conversion succeeded, or <c>null</c> if the conversion failed.
         /// </param>
         /// <returns><c>true</c> if s was converted successfully; otherwise, <c>false</c>.</returns>
-        public static bool TryParse(string text, out Style result)
+        public static bool TryParse(string text, out Style? result)
         {
             return StyleParser.TryParse(text, out result);
         }
@@ -113,13 +113,13 @@ namespace Spectre.Console
         }
 
         /// <inheritdoc/>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return Equals(obj as Style);
         }
 
         /// <inheritdoc/>
-        public bool Equals(Style other)
+        public bool Equals(Style? other)
         {
             if (other == null)
             {