Enable nullable reference types

src/WpfMath.Example/App.xaml.cs

@@ -12,7 +12,7 @@ public partial class App : Application
     {
         public static new App Current
         {
-            get { return Application.Current as App; }
+            get { return (App) Application.Current; }
         }
 
         private void Application_Startup(object sender, StartupEventArgs e)

src/WpfMath.Example/MainWindow.xaml.cs

@@ -37,10 +37,10 @@ public MainWindow()
             FormulaSelector.SelectedIndex = 0;
         }
 
-        private TexFormula ParseFormula(string input)
+        private TexFormula? ParseFormula(string input)
         {
             // Create formula object from input text.
-            TexFormula formula = null;
+            TexFormula? formula = null;
             try
             {
                 formula = this._formulaParser.Parse(input);

src/WpfMath.Example/WpfMath.Example.csproj

@@ -6,8 +6,15 @@
         <UseWpf>true</UseWpf>
         <DebugType>Full</DebugType>
         <IsPackable>false</IsPackable>
+        <Nullable>enable</Nullable>
     </PropertyGroup>
     <ItemGroup>
-        <ProjectReference Include="../WpfMath/WpfMath.csproj"/>
+        <ProjectReference Include="../WpfMath/WpfMath.csproj" />
+    </ItemGroup>
+    <ItemGroup>
+      <PackageReference Include="Nullable" Version="1.2.1">
+        <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        <PrivateAssets>all</PrivateAssets>
+      </PackageReference>
     </ItemGroup>
 </Project>

src/WpfMath/Atoms/AccentedAtom.cs

@@ -6,7 +6,7 @@ namespace WpfMath.Atoms
     // Atom representing base atom with accent above it.
     internal class AccentedAtom : Atom
     {
-        public AccentedAtom(SourceSpan source, Atom baseAtom, string accentName)
+        public AccentedAtom(SourceSpan? source, Atom? baseAtom, string accentName)
             : base(source)
         {
             this.BaseAtom = baseAtom;
@@ -16,7 +16,7 @@ public AccentedAtom(SourceSpan source, Atom baseAtom, string accentName)
                 throw new ArgumentException("The specified symbol name is not an accent.", "accent");
         }
 
-        public AccentedAtom(SourceSpan source, Atom baseAtom, TexFormula accent)
+        public AccentedAtom(SourceSpan? source, Atom? baseAtom, TexFormula accent)
             : base(source)
         {
             if (!(accent.RootAtom is SymbolAtom rootSymbol))
@@ -30,14 +30,14 @@ public AccentedAtom(SourceSpan source, Atom baseAtom, TexFormula accent)
         }
 
         // Atom over which accent symbol is placed.
-        public Atom BaseAtom { get; }
+        public Atom? BaseAtom { get; }
 
         // Atom representing accent symbol to place over base atom.
         public SymbolAtom AccentAtom { get; }
 
         protected override Box CreateBoxCore(TexEnvironment environment)
         {
-            CharSymbol GetBaseChar()
+            CharSymbol? GetBaseChar()
             {
                 var baseAtom = this.BaseAtom;
                 while (baseAtom is AccentedAtom a)

src/WpfMath/Atoms/Atom.cs

@@ -5,15 +5,15 @@ namespace WpfMath.Atoms
     // Atom (smallest unit) of TexFormula.
     internal abstract class Atom
     {
-        protected Atom(SourceSpan source, TexAtomType type = TexAtomType.Ordinary)
+        protected Atom(SourceSpan? source, TexAtomType type = TexAtomType.Ordinary)
         {
             this.Source = source;
             this.Type = type;
         }
 
         public TexAtomType Type { get; }
 
-        public SourceSpan Source { get; }
+        public SourceSpan? Source { get; }
 
         public Box CreateBox(TexEnvironment environment)
         {

src/WpfMath/Atoms/BigOperatorAtom.cs

@@ -16,17 +16,17 @@ private static Box ChangeWidth(Box box, double maxWidth)
         }
 
         public BigOperatorAtom(
-            SourceSpan source,
-            Atom baseAtom,
-            Atom lowerLimitAtom,
-            Atom upperLimitAtom,
+            SourceSpan? source,
+            Atom? baseAtom,
+            Atom? lowerLimitAtom,
+            Atom? upperLimitAtom,
             bool? useVerticalLimits = null)
             : this(source, baseAtom, lowerLimitAtom, upperLimitAtom)
         {
             this.UseVerticalLimits = useVerticalLimits;
         }
 
-        public BigOperatorAtom(SourceSpan source, Atom baseAtom, Atom lowerLimitAtom, Atom upperLimitAtom)
+        public BigOperatorAtom(SourceSpan? source, Atom? baseAtom, Atom? lowerLimitAtom, Atom? upperLimitAtom)
             : base(source, TexAtomType.BigOperator)
         {
             this.BaseAtom = baseAtom;
@@ -36,12 +36,12 @@ public BigOperatorAtom(SourceSpan source, Atom baseAtom, Atom lowerLimitAtom, At
         }
 
         // Atom representing big operator.
-        public Atom BaseAtom { get; }
+        public Atom? BaseAtom { get; }
 
         // Atoms representing lower and upper limits.
-        public Atom LowerLimitAtom { get; }
+        public Atom? LowerLimitAtom { get; }
 
-        public Atom UpperLimitAtom { get; }
+        public Atom? UpperLimitAtom { get; }
 
         // True if limits should be drawn over and under the base atom; false if they should be drawn as scripts.
         public bool? UseVerticalLimits { get; }
@@ -83,9 +83,9 @@ protected override Box CreateBoxCore(TexEnvironment environment)
             }
 
             // Create boxes for upper and lower limits.
-            var upperLimitBox = this.UpperLimitAtom == null ? null : this.UpperLimitAtom.CreateBox(
+            Box? upperLimitBox = this.UpperLimitAtom == null ? null : this.UpperLimitAtom.CreateBox(
                 environment.GetSuperscriptStyle());
-            var lowerLimitBox = this.LowerLimitAtom == null ? null : this.LowerLimitAtom.CreateBox(
+            Box? lowerLimitBox = this.LowerLimitAtom == null ? null : this.LowerLimitAtom.CreateBox(
                 environment.GetSubscriptStyle());
 
             // Make all component boxes equally wide.
@@ -106,28 +106,28 @@ protected override Box CreateBoxCore(TexEnvironment environment)
             if (this.UpperLimitAtom != null)
             {
                 resultBox.Add(new StrutBox(0, opSpacing5, 0, 0));
-                upperLimitBox.Shift = delta / 2;
+                upperLimitBox!.Shift = delta / 2;
                 resultBox.Add(upperLimitBox);
                 kern = Math.Max(texFont.GetBigOpSpacing1(style), texFont.GetBigOpSpacing3(style) -
                     upperLimitBox.Depth);
                 resultBox.Add(new StrutBox(0, kern, 0, 0));
             }
 
             // Add box for base atom.
-            resultBox.Add(baseBox);
+            resultBox.Add(baseBox!);
 
             // Create and add box for lower limit.
             if (this.LowerLimitAtom != null)
             {
                 resultBox.Add(new StrutBox(0, Math.Max(texFont.GetBigOpSpacing2(style), texFont.GetBigOpSpacing4(style) -
-                    lowerLimitBox.Height), 0, 0));
+                    lowerLimitBox!.Height), 0, 0));
                 lowerLimitBox.Shift = -delta / 2;
                 resultBox.Add(lowerLimitBox);
                 resultBox.Add(new StrutBox(0, opSpacing5, 0, 0));
             }
 
             // Adjust height and depth of result box.
-            var baseBoxHeight = baseBox.Height;
+            var baseBoxHeight = baseBox!.Height;
             var totalHeight = resultBox.Height + resultBox.Depth;
             if (upperLimitBox != null)
                 baseBoxHeight += opSpacing5 + kern + upperLimitBox.Height + upperLimitBox.Depth;

src/WpfMath/Atoms/CharAtom.cs

@@ -5,7 +5,7 @@ namespace WpfMath.Atoms
     // Atom representing single character in specific text style.
     internal class CharAtom : CharSymbol
     {
-        public CharAtom(SourceSpan source, char character, string textStyle = null)
+        public CharAtom(SourceSpan? source, char character, string? textStyle = null)
             : base(source)
         {
             this.TextStyle = textStyle;
@@ -15,7 +15,7 @@ public CharAtom(SourceSpan source, char character, string textStyle = null)
         public char Character { get; }
 
         // Null means default text style.
-        public string TextStyle { get; }
+        public string? TextStyle { get; }
 
         private bool IsDefaultTextStyle => this.TextStyle == null;
 
@@ -25,7 +25,7 @@ public override ITeXFont GetStyledFont(TexEnvironment environment) =>
         protected override Result<CharInfo> GetCharInfo(ITeXFont texFont, TexStyle style) =>
             this.IsDefaultTextStyle
                 ? texFont.GetDefaultCharInfo(this.Character, style)
-                : texFont.GetCharInfo(this.Character, this.TextStyle, style);
+                : texFont.GetCharInfo(this.Character, this.TextStyle!, style); // Nullable: CS8604, could be resolved by inlining IsDefaultTextStyle
 
         public override Result<CharFont> GetCharFont(ITeXFont texFont) =>
             // Style is irrelevant here.

src/WpfMath/Atoms/CharSymbol.cs

@@ -6,7 +6,7 @@ namespace WpfMath.Atoms
     // Atom representing single character that can be marked as text symbol.
     internal abstract class CharSymbol : Atom
     {
-        protected CharSymbol(SourceSpan source, TexAtomType type = TexAtomType.Ordinary)
+        protected CharSymbol(SourceSpan? source, TexAtomType type = TexAtomType.Ordinary)
             : base(source, type)
         {
             this.IsTextSymbol = false;

src/WpfMath/Atoms/DummyAtom.cs

@@ -18,7 +18,7 @@ public DummyAtom(Atom atom)
         {
         }
 
-        public Atom WithPreviousAtom(DummyAtom previousAtom)
+        public Atom WithPreviousAtom(DummyAtom? previousAtom)
         {
             if (this.Atom is IRow row)
             {

src/WpfMath/Atoms/FencedAtom.cs

@@ -15,7 +15,7 @@ private static void CentreBox(Box box, double axis)
             box.Shift = -(totalHeight / 2 - box.Height) - axis;
         }
 
-        public FencedAtom(SourceSpan source, Atom baseAtom, SymbolAtom leftDelimeter, SymbolAtom rightDelimeter)
+        public FencedAtom(SourceSpan? source, Atom? baseAtom, SymbolAtom? leftDelimeter, SymbolAtom? rightDelimeter)
             : base(source)
         {
             this.BaseAtom = baseAtom ?? new RowAtom(null);
@@ -25,9 +25,9 @@ public FencedAtom(SourceSpan source, Atom baseAtom, SymbolAtom leftDelimeter, Sy
 
         public Atom BaseAtom { get; }
 
-        private SymbolAtom LeftDelimeter { get; }
+        private SymbolAtom? LeftDelimeter { get; }
 
-        private SymbolAtom RightDelimeter { get; }
+        private SymbolAtom? RightDelimeter { get; }
 
         protected override Box CreateBoxCore(TexEnvironment environment)
         {

src/WpfMath/Atoms/FixedCharAtom.cs

@@ -5,7 +5,7 @@ namespace WpfMath.Atoms
     // Atom representing character that does not depend on text style.
     internal class FixedCharAtom : CharSymbol
     {
-        public FixedCharAtom(SourceSpan source, CharFont charFont)
+        public FixedCharAtom(SourceSpan? source, CharFont charFont)
             : base(source)
         {
             this.CharFont = charFont;

src/WpfMath/Atoms/FractionAtom.cs

@@ -23,9 +23,9 @@ private static TexAlignment CheckAlignment(TexAlignment alignment)
         private readonly double? lineRelativeThickness;
 
         public FractionAtom(
-            SourceSpan source,
-            Atom numerator,
-            Atom denominator,
+            SourceSpan? source,
+            Atom? numerator,
+            Atom? denominator,
             double relativeThickness,
             TexAlignment numeratorAlignment,
             TexAlignment denominatorAlignment)
@@ -35,9 +35,9 @@ public FractionAtom(
         }
 
         public FractionAtom(
-            SourceSpan source,
-            Atom numerator,
-            Atom denominator,
+            SourceSpan? source,
+            Atom? numerator,
+            Atom? denominator,
             bool drawLine,
             TexAlignment numeratorAlignment,
             TexAlignment denominatorAlignment)
@@ -47,15 +47,15 @@ public FractionAtom(
             this.denominatorAlignment = CheckAlignment(denominatorAlignment);
         }
 
-        public FractionAtom(SourceSpan source, Atom numerator, Atom denominator, bool drawLine)
+        public FractionAtom(SourceSpan? source, Atom? numerator, Atom? denominator, bool drawLine)
             : this(source, numerator, denominator, drawLine, TexUnit.Pixel, 0d)
         {
         }
 
         public FractionAtom(
-            SourceSpan source,
-            Atom numerator,
-            Atom denominator,
+            SourceSpan? source,
+            Atom? numerator,
+            Atom? denominator,
             TexUnit unit,
             double thickness,
             TexAlignment numeratorAlignment,
@@ -66,15 +66,15 @@ public FractionAtom(
             this.denominatorAlignment = CheckAlignment(denominatorAlignment);
         }
 
-        public FractionAtom(SourceSpan source, Atom numerator, Atom denominator, TexUnit unit, double thickness)
+        public FractionAtom(SourceSpan? source, Atom? numerator, Atom? denominator, TexUnit unit, double thickness)
             : this(source, numerator, denominator, false, unit, thickness)
         {
         }
 
         protected FractionAtom(
-            SourceSpan source,
-            Atom numerator,
-            Atom denominator,
+            SourceSpan? source,
+            Atom? numerator,
+            Atom? denominator,
             bool useDefaultThickness,
             TexUnit unit,
             double thickness)
@@ -91,9 +91,9 @@ protected FractionAtom(
             this.lineThickness = thickness;
         }
 
-        public Atom Numerator { get; }
+        public Atom? Numerator { get; }
 
-        public Atom Denominator { get; }
+        public Atom? Denominator { get; }
 
         protected override Box CreateBoxCore(TexEnvironment environment)
         {

src/WpfMath/Atoms/IRow.cs

@@ -6,6 +6,6 @@ namespace WpfMath
     internal interface IRow
     {
         // Dummy atom representing atom just before first child atom.
-        Atom WithPreviousAtom(DummyAtom previousAtom);
+        Atom WithPreviousAtom(DummyAtom? previousAtom);
     }
 }

src/WpfMath/Atoms/MatrixAtom.cs

@@ -13,20 +13,20 @@ internal class MatrixAtom : Atom
         public const double DefaultPadding = 0.35;
 
         public MatrixAtom(
-            SourceSpan source,
-            IEnumerable<IEnumerable<Atom>> cells,
+            SourceSpan? source,
+            IEnumerable<IEnumerable<Atom?>> cells,
             MatrixCellAlignment matrixCellAlignment,
             double verticalPadding = DefaultPadding,
             double horizontalPadding = DefaultPadding) : base(source)
         {
-            MatrixCells = new ReadOnlyCollection<ReadOnlyCollection<Atom>>(
-                cells.Select(row => new ReadOnlyCollection<Atom>(row.ToList())).ToList());
+            MatrixCells = new ReadOnlyCollection<ReadOnlyCollection<Atom?>>(
+                cells.Select(row => new ReadOnlyCollection<Atom?>(row.ToList())).ToList());
             MatrixCellAlignment = matrixCellAlignment;
             VerticalPadding = verticalPadding;
             HorizontalPadding = horizontalPadding;
         }
 
-        public ReadOnlyCollection<ReadOnlyCollection<Atom>> MatrixCells { get; }
+        public ReadOnlyCollection<ReadOnlyCollection<Atom?>> MatrixCells { get; }
 
         public double VerticalPadding { get; }
 
@@ -45,7 +45,7 @@ protected override Box CreateBoxCore(TexEnvironment environment)
             return ApplyCellPaddings(environment, cells, columnCount, matrixCellGaps);
         }
 
-        private IEnumerable<Box> CreateRowCellBoxes(TexEnvironment environment, ReadOnlyCollection<Atom> row) =>
+        private IEnumerable<Box> CreateRowCellBoxes(TexEnvironment environment, ReadOnlyCollection<Atom?> row) =>
             row.Select(atom => atom == null ? StrutBox.Empty : atom.CreateBox(environment));
 
         /// <summary>
@@ -142,7 +142,7 @@ Tuple<Box, Box> GetTopBottomPadding(int i, int j)
                 return new Tuple<Box, Box>(topBox, bottomBox);
             }
 
-            Tuple<Box, Box> GetLeftRightPadding(int i, int j)
+            Tuple<Box?, Box> GetLeftRightPadding(int i, int j)
             {
                 var value = matrixCellGaps[i][j].Horizontal;
                 var leftPadding = MatrixCellAlignment == MatrixCellAlignment.Left ? 0.0 : value;
@@ -151,7 +151,7 @@ Tuple<Box, Box> GetLeftRightPadding(int i, int j)
                     ? null
                     : new StrutBox(HorizontalPadding / 2 + leftPadding, 0.0, 0.0, 0.0);
                 var rightBox = new StrutBox(HorizontalPadding / 2 + rightPadding, 0.0, 0.0, 0.0);
-                return new Tuple<Box, Box>(leftBox, rightBox);
+                return new Tuple<Box?, Box>(leftBox, rightBox);
             }
         }
 

src/WpfMath/Atoms/NullAtom.cs

@@ -4,7 +4,7 @@ namespace WpfMath.Atoms
 {
     internal class NullAtom : Atom
     {
-        public NullAtom(SourceSpan source = null, TexAtomType type = TexAtomType.Ordinary) : base(source, type)
+        public NullAtom(SourceSpan? source = null, TexAtomType type = TexAtomType.Ordinary) : base(source, type)
         {
         }