Started working on nullable

src/AngleSharp.Css.nuspec

@@ -10,7 +10,7 @@
     <icon>logo.png</icon>
     <readme>README.md</readme>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
-    <description>Extends the CSSOM from the core AngleSharp library.</description>
+    <description>Extends the CSSOM from the core AngleSharp library. It parses CSS3 and is capable of performing a headless rendering evaluating the styles.</description>
     <releaseNotes>https://github.com/AngleSharp/AngleSharp.Css/blob/main/CHANGELOG.md</releaseNotes>
     <copyright>Copyright 2016-2024, AngleSharp</copyright>
     <tags>html html5 css css3 dom styling library anglesharp angle</tags>

src/AngleSharp.Css/AngleSharp.Css.csproj

@@ -4,10 +4,8 @@
     <RootNamespace>AngleSharp.Css</RootNamespace>
     <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netstandard2.0;net6.0;net7.0;net8.0</TargetFrameworks>
     <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">netstandard2.0;net461;net472;net6.0;net7.0;net8.0</TargetFrameworks>
-    <SignAssembly>true</SignAssembly>
-    <AssemblyOriginatorKeyFile>Key.snk</AssemblyOriginatorKeyFile>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
-    <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
     <RepositoryUrl>https://github.com/AngleSharp/AngleSharp.Css</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
     <PublishRepositoryUrl>true</PublishRepositoryUrl>

src/AngleSharp.Css/BrowsingContextExtensions.cs

@@ -20,7 +20,7 @@ public static class BrowsingContextExtensions
         /// <param name="address">The address of the resource.</param>
         /// <param name="element">The hosting element.</param>
         /// <returns>The async task.</returns>
-        public static Task<IStyleSheet> OpenStyleSheetAsync(this IBrowsingContext context, Url address, IElement element) =>
+        public static Task<IStyleSheet?> OpenStyleSheetAsync(this IBrowsingContext context, Url address, IElement element) =>
             context.OpenStyleSheetAsync(address, element, CancellationToken.None);
 
         /// <summary>
@@ -31,21 +31,20 @@ public static Task<IStyleSheet> OpenStyleSheetAsync(this IBrowsingContext contex
         /// <param name="element">The hosting element.</param>
         /// <param name="cancel">The cancellation token.</param>
         /// <returns>The async task.</returns>
-        public static async Task<IStyleSheet> OpenStyleSheetAsync(this IBrowsingContext context, Url address, IElement element, CancellationToken cancel)
+        public static async Task<IStyleSheet?> OpenStyleSheetAsync(this IBrowsingContext context, Url address, IElement element, CancellationToken cancel)
         {
             var loader = context.GetService<IResourceLoader>();
             var service = context.GetCssStyling();
 
-            if (loader != null && service != null)
+            if (loader is not null && service is not null)
             {
                 var request = element.CreateRequestFor(address);
                 var download = loader.FetchAsync(request);
 
-                using (var response = await download.Task.ConfigureAwait(false))
-                {
-                    var options = new StyleOptions(element?.Owner ?? context.Active) { Element = element };
-                    return await service.ParseStylesheetAsync(response, options, cancel).ConfigureAwait(false);
-                }
+                using var response = await download.Task.ConfigureAwait(false);
+                var document = element.Owner ?? context.Active ?? throw new InvalidOperationException("Could not find a related documented.");
+                var options = new StyleOptions(document) { Element = element };
+                return await service.ParseStylesheetAsync(response, options, cancel).ConfigureAwait(false);
             }
 
             return null;
@@ -57,7 +56,7 @@ internal static DeclarationInfo GetDeclarationInfo(this IBrowsingContext context
             return factory.Create(propertyName);
         }
 
-        internal static ICssProperty CreateShorthand(this IBrowsingContext context, String name, ICssValue[] longhands, Boolean important)
+        internal static ICssProperty? CreateShorthand(this IBrowsingContext context, String name, ICssValue[] longhands, Boolean important)
         {
             var factory = context.GetFactory<IDeclarationFactory>();
             var info = factory.Create(name);
@@ -79,7 +78,7 @@ internal static ICssProperty[] CreateLonghands(this IBrowsingContext context, IC
             return factory.CreateProperties(info.Longhands, values, shorthand.IsImportant);
         }
 
-        internal static CssProperty CreateProperty(this IBrowsingContext context, String propertyName)
+        internal static CssProperty? CreateProperty(this IBrowsingContext context, String propertyName)
         {
             var info = context.GetDeclarationInfo(propertyName);
 
@@ -102,7 +101,7 @@ private static Boolean IsAllowingUnknownDeclarations(this IBrowsingContext conte
 
         private static ICssProperty[] CreateProperties(this IDeclarationFactory factory, String[] names, ICssValue[] values, Boolean important)
         {
-            if (values != null && values.Length == names.Length)
+            if (values.Length == names.Length)
             {
                 var properties = new ICssProperty[names.Length];
 
@@ -115,7 +114,7 @@ private static ICssProperty[] CreateProperties(this IDeclarationFactory factory,
                 return properties;
             }
 
-            return null;
+            return [];
         }
     }
 }

src/AngleSharp.Css/Constants/InitialValues.cs

@@ -18,7 +18,7 @@ static class InitialValues
         public static readonly ICssValue BackgroundRepeatDecl = new CssImageRepeatsValue(BackgroundRepeatHorizontalDecl, BackgroundRepeatVerticalDecl);
         public static readonly ICssValue BackgroundPositionXDecl = new CssLengthValue(0, CssLengthValue.Unit.Percent);
         public static readonly ICssValue BackgroundPositionYDecl = new CssLengthValue(0, CssLengthValue.Unit.Percent);
-        public static readonly ICssValue BackgroundPositionDecl = new CssTupleValue(new [] { BackgroundPositionXDecl, BackgroundPositionYDecl });
+        public static readonly ICssValue BackgroundPositionDecl = new CssTupleValue([BackgroundPositionXDecl, BackgroundPositionYDecl]);
         public static readonly ICssValue BackgroundSizeDecl = new CssBackgroundSizeValue(new CssConstantValue<CssLengthValue>(CssKeywords.Auto, CssLengthValue.Auto), new CssConstantValue<CssLengthValue>(CssKeywords.Auto, CssLengthValue.Auto));
         public static readonly ICssValue BackgroundOriginDecl = new CssConstantValue<BoxModel>(CssKeywords.BorderBox, BoxModel.PaddingBox);
         public static readonly ICssValue BackgroundClipDecl = new CssConstantValue<BoxModel>(CssKeywords.BorderBox, BoxModel.BorderBox);
@@ -204,13 +204,13 @@ static class InitialValues
         public static readonly ICssValue ZIndexDecl = new CssConstantValue<CssLengthValue>(CssKeywords.Auto, CssLengthValue.Auto);
         public static readonly ICssValue WidthDecl = CssLengthValue.Auto;
         public static readonly ICssValue HeightDecl = CssLengthValue.Auto;
-        public static readonly ICssValue ScrollbarTrackColorDecl = CssColors.GetColor("scrollbar");
-        public static readonly ICssValue ScrollbarShadowColorDecl = CssColors.GetColor("threeddarkshadow");
-        public static readonly ICssValue ScrollbarHighlightColorDecl = CssColors.GetColor("threedhighlight");
-        public static readonly ICssValue ScrollbarFaceColorDecl = CssColors.GetColor("threedface");
-        public static readonly ICssValue ScrollbarDarkshadowColorDecl = CssColors.GetColor("threeddarkshadow");
+        public static readonly ICssValue ScrollbarTrackColorDecl = CssColors.GetColor("scrollbar")!;
+        public static readonly ICssValue ScrollbarShadowColorDecl = CssColors.GetColor("threeddarkshadow")!;
+        public static readonly ICssValue ScrollbarHighlightColorDecl = CssColors.GetColor("threedhighlight")!;
+        public static readonly ICssValue ScrollbarFaceColorDecl = CssColors.GetColor("threedface")!;
+        public static readonly ICssValue ScrollbarDarkshadowColorDecl = CssColors.GetColor("threeddarkshadow")!;
         public static readonly ICssValue ScrollbarBaseColorDecl = CssColorValue.Transparent;
-        public static readonly ICssValue ScrollbarArrowColorDecl = CssColors.GetColor("buttontext");
+        public static readonly ICssValue ScrollbarArrowColorDecl = CssColors.GetColor("buttontext")!;
         public static readonly ICssValue Scrollbar3dLightColorDecl = CssColorValue.White;
         public static readonly ICssValue LetterSpacingDecl = CssLengthValue.Normal;
         public static readonly ICssValue FontSizeAdjustDecl = new CssLengthValue(1.0, CssLengthValue.Unit.Em);

src/AngleSharp.Css/Converters/ClassValueConverter.cs

@@ -4,15 +4,10 @@
     using AngleSharp.Text;
     using System;
 
-    sealed class ClassValueConverter<T> : IValueConverter
+    sealed class ClassValueConverter<T>(Func<StringSource, T> converter) : IValueConverter
         where T : class, ICssValue
     {
-        private readonly Func<StringSource, T> _converter;
-
-        public ClassValueConverter(Func<StringSource, T> converter)
-        {
-            _converter = converter;
-        }
+        private readonly Func<StringSource, T> _converter = converter;
 
         public ICssValue Convert(StringSource source)
         {

src/AngleSharp.Css/Converters/CounterValueConverter.cs

@@ -4,23 +4,17 @@ namespace AngleSharp.Css.Converters
     using AngleSharp.Css.Parser;
     using AngleSharp.Css.Values;
     using AngleSharp.Text;
-    using System;
     using System.Collections.Generic;
 
-    sealed class CounterValueConverter : IValueConverter
+    sealed class CounterValueConverter(ICssValue defaultValue) : IValueConverter
     {
-        private static readonly CssCounterValue[] NoneValue = Array.Empty<CssCounterValue>();
+        private static readonly CssCounterValue[] NoneValue = [];
 
-        private readonly ICssValue _defaultValue;
+        private readonly ICssValue _defaultValue = defaultValue;
 
-        public CounterValueConverter(ICssValue defaultValue)
+        public ICssValue? Convert(StringSource source)
         {
-            _defaultValue = defaultValue;
-        }
-
-        public ICssValue Convert(StringSource source)
-        {
-            var counters = new List<CssCounterValue>();
+            var counters = new List<ICssValue>();
 
             if (!source.IsIdentifier(CssKeywords.None))
             {
@@ -39,7 +33,7 @@ public ICssValue Convert(StringSource source)
                     counters.Add(new CssCounterValue(name, value));
                 }
 
-                return new CssTupleValue<CssCounterValue>(counters.ToArray());
+                return new CssTupleValue([.. counters]);
             }
 
             return new CssConstantValue<CssCounterValue[]>(CssKeywords.None, NoneValue);

src/AngleSharp.Css/Converters/DictionaryValueConverter.cs

@@ -7,22 +7,16 @@ namespace AngleSharp.Css.Converters
     using System;
     using System.Collections.Generic;
 
-    sealed class DictionaryValueConverter<T> : IValueConverter
+    sealed class DictionaryValueConverter<T>(IDictionary<String, T> values) : IValueConverter
     {
-        private readonly IDictionary<String, T> _values;
+        private readonly IDictionary<String, T> _values = values;
 
-        public DictionaryValueConverter(IDictionary<String, T> values)
-        {
-            _values = values;
-        }
-
-        public ICssValue Convert(StringSource source)
+        public ICssValue? Convert(StringSource source)
         {
             var pos = source.Index;
             var ident = source.ParseIdent();
-            var mode = default(T);
 
-            if (ident != null && _values.TryGetValue(ident, out mode))
+            if (ident is not null && _values.TryGetValue(ident, out var mode))
             {
                 return new CssConstantValue<T>(ident.ToLowerInvariant(), mode);
             }

src/AngleSharp.Css/Converters/FlowRelativeValueConverter.cs

@@ -6,28 +6,23 @@ namespace AngleSharp.Css.Converters
     using AngleSharp.Text;
     using System;
 
-    sealed class FlowRelativeValueConverter : IValueConverter
+    sealed class FlowRelativeValueConverter(IValueConverter converter) : IValueConverter
     {
-        private readonly IValueConverter _converter;
+        private readonly IValueConverter _converter = converter;
 
-        public FlowRelativeValueConverter(IValueConverter converter)
-        {
-            _converter = converter;
-        }
-
-        public ICssValue Convert(StringSource source)
+        public ICssValue? Convert(StringSource source)
         {
             var options = new ICssValue[2];
             var length = 0;
 
             for (var i = 0; i < options.Length; i++)
             {
-                options[i] = _converter.Convert(source);
+                var option = _converter.Convert(source);
                 source.SkipSpacesAndComments();
 
-                if (options[length] != null)
+                if (option is not null)
                 {
-                    length++;
+                    options[length++] = option;
                 }
             }
 

src/AngleSharp.Css/Converters/IdentifierValueConverter.cs

@@ -6,20 +6,15 @@ namespace AngleSharp.Css.Converters
     using AngleSharp.Text;
     using System;
 
-    sealed class IdentifierValueConverter : IValueConverter
+    sealed class IdentifierValueConverter(Func<StringSource, String> check) : IValueConverter
     {
-        private readonly Func<StringSource, String> _check;
+        private readonly Func<StringSource, String> _check = check;
 
-        public IdentifierValueConverter(Func<StringSource, String> check)
-        {
-            _check = check;
-        }
-
-        public ICssValue Convert(StringSource source)
+        public ICssValue? Convert(StringSource source)
         {
             var result = _check.Invoke(source);
 
-            if (result != null)
+            if (result is not null)
             {
                 return new CssIdentifierValue(result);
             }
@@ -28,18 +23,12 @@ public ICssValue Convert(StringSource source)
         }
     }
 
-    sealed class IdentifierValueConverter<T> : IValueConverter
+    sealed class IdentifierValueConverter<T>(String identifier, T result) : IValueConverter
     {
-        private readonly String _identifier;
-        private readonly T _result;
-
-        public IdentifierValueConverter(String identifier, T result)
-        {
-            _identifier = identifier;
-            _result = result;
-        }
+        private readonly String _identifier = identifier;
+        private readonly T _result = result;
 
-        public ICssValue Convert(StringSource source)
+        public ICssValue? Convert(StringSource source)
         {
             if (source.IsIdentifier(_identifier))
             {

src/AngleSharp.Css/Converters/ListValueConverter.cs

@@ -6,16 +6,11 @@ namespace AngleSharp.Css.Converters
     using AngleSharp.Text;
     using System.Collections.Generic;
 
-    sealed class ListValueConverter : IValueConverter
+    sealed class ListValueConverter(IValueConverter converter) : IValueConverter
     {
-        private readonly IValueConverter _converter;
+        private readonly IValueConverter _converter = converter;
 
-        public ListValueConverter(IValueConverter converter)
-        {
-            _converter = converter;
-        }
-
-        public ICssValue Convert(StringSource source)
+        public ICssValue? Convert(StringSource source)
         {
             var values = new List<ICssValue>();
 
@@ -33,7 +28,7 @@ public ICssValue Convert(StringSource source)
                 values.Add(value);
             }
 
-            return values.Count > 0 ? new CssListValue(values.ToArray()) : null;
+            return values.Count > 0 ? new CssListValue([.. values]) : null;
         }
     }
 }

src/AngleSharp.Css/Converters/OneOrMoreValueConverter.cs

@@ -7,22 +7,14 @@ namespace AngleSharp.Css.Converters
     using System;
     using System.Collections.Generic;
 
-    sealed class OneOrMoreValueConverter : IValueConverter
+    sealed class OneOrMoreValueConverter(IValueConverter converter, Int32 minimum, Int32 maximum, String separator) : IValueConverter
     {
-        private readonly IValueConverter _converter;
-        private readonly Int32 _minimum;
-        private readonly Int32 _maximum;
-        private readonly String _separator;
+        private readonly IValueConverter _converter = converter;
+        private readonly Int32 _minimum = minimum;
+        private readonly Int32 _maximum = maximum;
+        private readonly String _separator = separator;
 
-        public OneOrMoreValueConverter(IValueConverter converter, Int32 minimum, Int32 maximum, String separator)
-        {
-            _converter = converter;
-            _minimum = minimum;
-            _maximum = maximum;
-            _separator = separator;
-        }
-
-        public ICssValue Convert(StringSource source)
+        public ICssValue? Convert(StringSource source)
         {
             var values = new List<ICssValue>();
 
@@ -37,7 +29,7 @@ public ICssValue Convert(StringSource source)
                 values.Add(value);
             }
 
-            return values.Count >= _minimum ? new CssTupleValue(values.ToArray(), _separator) : null;
+            return values.Count >= _minimum ? new CssTupleValue([.. values], _separator) : null;
         }
     }
 }

src/AngleSharp.Css/Converters/OptionValueConverter.cs

@@ -4,18 +4,12 @@ namespace AngleSharp.Css.Converters
     using AngleSharp.Css.Values;
     using AngleSharp.Text;
 
-    sealed class OptionValueConverter : IValueConverter
+    sealed class OptionValueConverter(IValueConverter converter, ICssValue defaultValue) : IValueConverter
     {
-        private readonly IValueConverter _converter;
-        private readonly ICssValue _defaultValue;
+        private readonly IValueConverter _converter = converter;
+        private readonly ICssValue _defaultValue = defaultValue;
 
-        public OptionValueConverter(IValueConverter converter, ICssValue defaultValue)
-        {
-            _converter = converter;
-            _defaultValue = defaultValue;
-        }
-
-        public ICssValue Convert(StringSource source)
+        public ICssValue? Convert(StringSource source)
         {
             if (source.IsDone || source.Current == Symbols.Comma)
             {