Add nullability support for NRules

src/NRules/NRules.Fluent/Dsl/ContextExtensions.cs

@@ -13,6 +13,7 @@ public static class ContextExtensions
     /// <param name="fact">Existing fact to update.</param>
     /// <param name="updateAction">Action to apply to the fact.</param>
     public static void Update<T>(this IContext context, T fact, Action<T> updateAction)
+        where T : notnull
     {
         updateAction(fact);
         context.Update(fact);

src/NRules/NRules.Fluent/Dsl/IFilterExpression.cs

@@ -14,7 +14,7 @@ public interface IFilterExpression
     /// </summary>
     /// <param name="keySelectors">Key selector expressions.</param>
     /// <returns>Filters expression builder.</returns>
-    IFilterExpression OnChange(params Expression<Func<object>>[] keySelectors);
+    IFilterExpression OnChange(params Expression<Func<object?>>[] keySelectors);
 
     /// <summary>
     /// Configures the engine to filter rule's matches given a set of predicates.

src/NRules/NRules.Fluent/Expressions/FilterExpression.cs

@@ -17,7 +17,7 @@ public FilterExpression(FilterGroupBuilder builder, SymbolStack symbolStack)
         _symbolStack = symbolStack;
     }
 
-    public IFilterExpression OnChange(params Expression<Func<object>>[] keySelectors)
+    public IFilterExpression OnChange(params Expression<Func<object?>>[] keySelectors)
     {
         foreach (var keySelector in keySelectors)
         {

src/NRules/NRules.Fluent/Expressions/LeftHandSideExpression.cs

@@ -9,7 +9,7 @@ internal class LeftHandSideExpression : ILeftHandSideExpression
 {
     private readonly GroupBuilder _builder;
     private readonly SymbolStack _symbolStack;
-    private PatternBuilder _currentPatternBuilder;
+    private PatternBuilder? _currentPatternBuilder;
 
     public LeftHandSideExpression(GroupBuilder builder, SymbolStack symbolStack)
     {
@@ -29,7 +29,7 @@ public ILeftHandSideExpression Match<TFact>(Expression<Func<TFact>> alias, param
 
     public ILeftHandSideExpression Match<TFact>(params Expression<Func<TFact, bool>>[] conditions)
     {
-        var symbol = Expression.Parameter(typeof (TFact));
+        var symbol = Expression.Parameter(typeof(TFact));
         var patternBuilder = _builder.Pattern(symbol.Type, symbol.Name);
         patternBuilder.DslConditions(_symbolStack.Scope.Declarations, conditions);
         _symbolStack.Scope.Add(patternBuilder.Declaration);

src/NRules/NRules.Fluent/Expressions/PatternExpressionRewriter.cs

@@ -8,8 +8,8 @@ namespace NRules.Fluent.Expressions;
 internal class PatternExpressionRewriter : ExpressionRewriter
 {
     private readonly Declaration _patternDeclaration;
-    private ParameterExpression _originalParameter;
-    private ParameterExpression _normalizedParameter;
+    private ParameterExpression? _originalParameter;
+    private ParameterExpression? _normalizedParameter;
 
     public PatternExpressionRewriter(Declaration patternDeclaration, IEnumerable<Declaration> declarations)
         : base(declarations)

src/NRules/NRules.Fluent/Expressions/QueryExpression.cs

@@ -13,7 +13,7 @@ internal class QueryExpression : IQuery, IQueryBuilder
     private readonly ParameterExpression _symbol;
     private readonly SymbolStack _symbolStack;
     private readonly GroupBuilder _groupBuilder;
-    private Func<string, Type, BuildResult> _buildAction;
+    private Func<string?, Type?, BuildResult>? _buildAction;
 
     public QueryExpression(ParameterExpression symbol, SymbolStack symbolStack, GroupBuilder groupBuilder)
     {
@@ -52,7 +52,7 @@ public void From<TSource>(Expression<Func<TSource>> source)
 
     public void Where<TSource>(Expression<Func<TSource, bool>>[] predicates)
     {
-        var previousBuildAction = _buildAction;
+        var previousBuildAction = EnsureBuildAction();
         _buildAction = (name, type) =>
         {
             var result = previousBuildAction(name, type);
@@ -63,7 +63,7 @@ public void Where<TSource>(Expression<Func<TSource, bool>>[] predicates)
 
     public void Select<TSource, TResult>(Expression<Func<TSource, TResult>> selector)
     {
-        var previousBuildAction = _buildAction;
+        var previousBuildAction = EnsureBuildAction();
         _buildAction = (name, _) =>
         {
             var patternBuilder = new PatternBuilder(typeof(TResult), name);
@@ -87,7 +87,7 @@ public void Where<TSource>(Expression<Func<TSource, bool>>[] predicates)
 
     public void SelectMany<TSource, TResult>(Expression<Func<TSource, IEnumerable<TResult>>> selector)
     {
-        var previousBuildAction = _buildAction;
+        var previousBuildAction = EnsureBuildAction();
         _buildAction = (name, _) =>
         {
             var patternBuilder = new PatternBuilder(typeof(TResult), name);
@@ -111,7 +111,7 @@ public void Where<TSource>(Expression<Func<TSource, bool>>[] predicates)
 
     public void GroupBy<TSource, TKey, TElement>(Expression<Func<TSource, TKey>> keySelector, Expression<Func<TSource, TElement>> elementSelector)
     {
-        var previousBuildAction = _buildAction;
+        var previousBuildAction = EnsureBuildAction();
         _buildAction = (name, _) =>
         {
             var patternBuilder = new PatternBuilder(typeof(IGrouping<TKey, TElement>), name);
@@ -136,7 +136,7 @@ public void Where<TSource>(Expression<Func<TSource, bool>>[] predicates)
 
     public void Collect<TSource>()
     {
-        var previousBuildAction = _buildAction;
+        var previousBuildAction = EnsureBuildAction();
         _buildAction = (name, type) =>
         {
             var patternBuilder = new PatternBuilder(type ?? typeof(IEnumerable<TSource>), name);
@@ -160,10 +160,14 @@ public void Collect<TSource>()
 
     public void ToLookup<TSource, TKey, TElement>(Expression<Func<TSource, TKey>> keySelector, Expression<Func<TSource, TElement>> elementSelector)
     {
-        var previousBuildAction = _buildAction;
+        var previousBuildAction = EnsureBuildAction();
         _buildAction = (name, _) =>
         {
             var result = previousBuildAction(name, typeof(IKeyedLookup<TKey, TElement>));
+            if (result.Source is null || result.Aggregate is null)
+            {
+                throw new InvalidOperationException($"{nameof(ToLookup)} cannot be called directly after {nameof(From)} or {nameof(FactQuery)}");
+            }
             var keySelectorExpression = result.Source.DslPatternExpression(_symbolStack.Scope.Declarations, keySelector);
             var elementSelectorExpression = result.Source.DslPatternExpression(_symbolStack.Scope.Declarations, elementSelector);
             result.Aggregate.ToLookup(keySelectorExpression, elementSelectorExpression);
@@ -173,10 +177,14 @@ public void Collect<TSource>()
 
     public void OrderBy<TSource, TKey>(Expression<Func<TSource, TKey>> keySelector, SortDirection sortDirection)
     {
-        var previousBuildAction = _buildAction;
+        var previousBuildAction = EnsureBuildAction();
         _buildAction = (name, type) =>
         {
             var result = previousBuildAction(name, type);
+            if (result.Source is null || result.Aggregate is null)
+            {
+                throw new InvalidOperationException($"{nameof(OrderBy)} cannot be called directly after {nameof(From)} or {nameof(FactQuery)}");
+            }
             var keySelectorExpression = result.Source.DslPatternExpression(_symbolStack.Scope.Declarations, keySelector);
             result.Aggregate.OrderBy(keySelectorExpression, sortDirection);
             return result;
@@ -188,9 +196,9 @@ public void Collect<TSource>()
         Aggregate<TSource, TResult>(aggregateName, expressions, null);
     }
 
-    public void Aggregate<TSource, TResult>(string aggregateName, IEnumerable<KeyValuePair<string, LambdaExpression>> expressions, Type customFactoryType)
+    public void Aggregate<TSource, TResult>(string aggregateName, IEnumerable<KeyValuePair<string, LambdaExpression>> expressions, Type? customFactoryType)
     {
-        var previousBuildAction = _buildAction;
+        var previousBuildAction = EnsureBuildAction();
         _buildAction = (name, _) =>
         {
             var patternBuilder = new PatternBuilder(typeof(TResult), name);
@@ -222,11 +230,16 @@ public void Collect<TSource>()
 
     public PatternBuilder Build()
     {
-        var patternBuilder = _buildAction(_symbol.Name, null);
+        var patternBuilder = EnsureBuildAction()(_symbol.Name, null);
         _groupBuilder.Pattern(patternBuilder.Pattern);
         return patternBuilder.Pattern;
     }
-
+
+    private Func<string?, Type?, BuildResult> EnsureBuildAction()
+    {
+        return _buildAction ?? throw new InvalidOperationException($"{nameof(From)} or {nameof(FactQuery)} was not called");
+    }
+
     private class BuildResult
     {
         public BuildResult(PatternBuilder pattern, AggregateBuilder aggregate, PatternBuilder source)
@@ -242,7 +255,7 @@ public BuildResult(PatternBuilder pattern)
         }
 
         public PatternBuilder Pattern { get; }
-        public AggregateBuilder Aggregate { get; }
-        public PatternBuilder Source { get; }
+        public AggregateBuilder? Aggregate { get; }
+        public PatternBuilder? Source { get; }
     }
 }

src/NRules/NRules.Fluent/Expressions/SymbolTable.cs

@@ -7,7 +7,7 @@ namespace NRules.Fluent.Expressions;
 internal class SymbolTable
 {
     private readonly HashSet<Declaration> _declarations;
-    private readonly SymbolTable _parentScope;
+    private readonly SymbolTable? _parentScope;
 
     internal SymbolTable()
     {

src/NRules/NRules.Fluent/NRules.Fluent.csproj

@@ -8,6 +8,7 @@
     <SignAssembly>True</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\..\SigningKey.snk</AssemblyOriginatorKeyFile>
     <LangVersion>latest</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/NRules/NRules.Fluent/RuleLoadSpec.cs

@@ -34,7 +34,7 @@ public interface IRuleLoadSpec
     /// <param name="assemblies">Assemblies to load from.</param>
     /// <returns>Spec to continue fluent configuration.</returns>
     IRuleLoadSpec From(params Assembly[] assemblies);
-    
+
     /// <summary>
     /// Specifies to load all rule definitions from a given collection of assemblies.
     /// </summary>
@@ -83,14 +83,14 @@ internal class RuleLoadSpec : IRuleLoadSpec
 {
     private readonly IRuleActivator _activator;
     private readonly RuleTypeScanner _typeScanner = new();
-    private Func<IRuleMetadata, bool> _filter;
+    private Func<IRuleMetadata, bool>? _filter;
 
     public RuleLoadSpec(IRuleActivator activator)
     {
         _activator = activator;
     }
 
-    public string RuleSetName { get; private set; }
+    public string? RuleSetName { get; private set; }
 
     public IRuleLoadSpec PrivateTypes(bool include = true)
     {
@@ -136,9 +136,9 @@ public IRuleLoadSpec From(Action<IRuleTypeScanner> scanAction)
 
     public IRuleLoadSpec Where(Func<IRuleMetadata, bool> filter)
     {
-        if (IsFilterSet())
+        if (_filter != null)
             throw new InvalidOperationException("Rule load specification can only have a single 'Where' clause");
-        
+
         _filter = filter;
         return this;
     }
@@ -147,7 +147,7 @@ public IRuleLoadSpec To(string ruleSetName)
     {
         if (RuleSetName != null)
             throw new InvalidOperationException("Rule load specification can only have a single 'To' clause");
-        
+
         RuleSetName = ruleSetName;
         return this;
     }
@@ -164,7 +164,7 @@ public IEnumerable<IRuleDefinition> Load()
     private IEnumerable<Type> GetRuleTypes()
     {
         var ruleTypes = _typeScanner.GetRuleTypes();
-        if (IsFilterSet())
+        if (_filter != null)
         {
             var metadata = ruleTypes.Select(ruleType => new RuleMetadata(ruleType));
             var filteredTypes = metadata.Where(x => _filter(x)).Select(x => x.RuleType);
@@ -185,9 +185,4 @@ private IEnumerable<Rule> Activate(Type type)
             throw new RuleActivationException("Failed to activate rule type", type, e);
         }
     }
-
-    private bool IsFilterSet()
-    {
-        return _filter != null;
-    }
 }

src/NRules/NRules.Json/Converters/ExpressionConverter.cs

@@ -180,7 +180,8 @@ private void WriteLambda(Utf8JsonWriter writer, JsonSerializerOptions options, L
 
     private ConstantExpression ReadConstant(ref Utf8JsonReader reader, JsonSerializerOptions options)
     {
-        var type = reader.ReadProperty<Type>(nameof(ConstantExpression.Type), options);
+        var type = reader.ReadProperty<Type>(nameof(ConstantExpression.Type), options)
+            ?? throw new JsonException($"Property '{nameof(ConstantExpression.Type)}' should have not null value");
         var value = reader.ReadProperty(nameof(ConstantExpression.Value), type, options);
         return Expression.Constant(value, type);
     }
@@ -238,10 +239,12 @@ private void WriteMethodCall(Utf8JsonWriter writer, JsonSerializerOptions option
 
     private BinaryExpression ReadBinaryExpression(ref Utf8JsonReader reader, JsonSerializerOptions options, ExpressionType expressionType)
     {
-        var left = reader.ReadProperty<Expression>(nameof(BinaryExpression.Left), options);
-        var right = reader.ReadProperty<Expression>(nameof(BinaryExpression.Right), options);
+        var left = reader.ReadProperty<Expression>(nameof(BinaryExpression.Left), options)
+            ?? throw new JsonException($"Property '{nameof(BinaryExpression.Left)}' should have not null value");
+        var right = reader.ReadProperty<Expression>(nameof(BinaryExpression.Right), options)
+            ?? throw new JsonException($"Property '{nameof(BinaryExpression.Right)}' should have not null value");
 
-        MethodInfo method = default;
+        MethodInfo? method = default;
         if (reader.TryReadMethodInfo(options, out var methodRecord))
             method = methodRecord.GetMethod(new[] { left.Type, right.Type }, left.Type);
 
@@ -313,10 +316,11 @@ private void WriteBinaryExpression(Utf8JsonWriter writer, JsonSerializerOptions
 
     private UnaryExpression ReadUnaryExpression(ref Utf8JsonReader reader, JsonSerializerOptions options, ExpressionType expressionType)
     {
-        var operand = reader.ReadProperty<Expression>(nameof(UnaryExpression.Operand), options);
+        var operand = reader.ReadProperty<Expression>(nameof(UnaryExpression.Operand), options)
+            ?? throw new JsonException($"Property '{nameof(UnaryExpression.Operand)}' should have not null value");
         reader.TryReadProperty<Type>(nameof(UnaryExpression.Type), options, out var type);
 
-        MethodInfo method = default;
+        MethodInfo? method = default;
         if (reader.TryReadMethodInfo(options, out var methodRecord))
             method = methodRecord.GetMethod(new[] { operand.Type }, operand.Type);
 
@@ -379,7 +383,8 @@ private void WriteTypeBinaryExpression(Utf8JsonWriter writer, JsonSerializerOpti
 
     private NewExpression ReadNewExpression(ref Utf8JsonReader reader, JsonSerializerOptions options)
     {
-        var declaringType = reader.ReadProperty<Type>(nameof(NewExpression.Constructor.DeclaringType), options);
+        var declaringType = reader.ReadProperty<Type>(nameof(NewExpression.Constructor.DeclaringType), options)
+            ?? throw new JsonException($"Property '{nameof(NewExpression.Constructor.DeclaringType)}' should have not null value");
         reader.TryReadArrayProperty<Expression>(nameof(NewExpression.Arguments), options, out var arguments);
 
         var ctor = declaringType.GetConstructor(arguments.Select(x => x.Type).ToArray())

src/NRules/NRules.Json/Converters/ExpressionElementConverter.cs

@@ -13,8 +13,10 @@ internal class NamedExpressionElementConverter : JsonConverter<NamedExpressionEl
     public override NamedExpressionElement Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
     {
         reader.ReadStartObject();
-        var name = reader.ReadStringProperty(nameof(NamedExpressionElement.Name), options);
-        var expression = reader.ReadProperty<LambdaExpression>(nameof(NamedExpressionElement.Expression), options);
+        var name = reader.ReadStringProperty(nameof(NamedExpressionElement.Name), options)
+            ?? throw new JsonException($"Property '{nameof(NamedExpressionElement.Name)}' should have not null value");
+        var expression = reader.ReadProperty<LambdaExpression>(nameof(NamedExpressionElement.Expression), options)
+            ?? throw new JsonException($"Property '{nameof(NamedExpressionElement.Expression)}' should have not null value");
         return Element.Expression(name, expression);
     }
 
@@ -34,15 +36,16 @@ public override ActionElement Read(ref Utf8JsonReader reader, Type typeToConvert
         reader.ReadStartObject();
         if (!reader.TryReadEnumProperty<ActionTrigger>(nameof(ActionElement.ActionTrigger), options, out var trigger))
             trigger = ActionElement.DefaultTrigger;
-        var expression = reader.ReadProperty<LambdaExpression>(nameof(ActionElement.Expression), options);
+        var expression = reader.ReadProperty<LambdaExpression>(nameof(ActionElement.Expression), options)
+            ?? throw new JsonException($"Property '{nameof(ActionElement.Expression)}' should have not null value");
         return Element.Action(expression, trigger);
     }
 
     public override void Write(Utf8JsonWriter writer, ActionElement value, JsonSerializerOptions options)
     {
         writer.WriteStartObject();
         if (value.ActionTrigger != ActionElement.DefaultTrigger)
-            writer.WriteEnumProperty(nameof(ActionElement.ActionTrigger), value.ActionTrigger, options); 
+            writer.WriteEnumProperty(nameof(ActionElement.ActionTrigger), value.ActionTrigger, options);
         writer.WriteProperty(nameof(ActionElement.Expression), value.Expression, options);
         writer.WriteEndObject();
     }

src/NRules/NRules.Json/Converters/MemberBindingExtensions.cs

@@ -7,7 +7,7 @@ namespace NRules.Json.Converters;
 
 internal static class MemberBindingExtensions
 {
-    public static MemberBinding ReadMemberBinding(this ref Utf8JsonReader reader, JsonSerializerOptions options, Type impiedType = null)
+    public static MemberBinding ReadMemberBinding(this ref Utf8JsonReader reader, JsonSerializerOptions options, Type? impiedType = null)
     {
         var bindingType = reader.ReadEnumProperty<MemberBindingType>(nameof(MemberBinding.BindingType), options);
 
@@ -20,7 +20,7 @@ public static MemberBinding ReadMemberBinding(this ref Utf8JsonReader reader, Js
         }
     }
 
-    public static void WriteMemberBinding(this Utf8JsonWriter writer, MemberBinding value, JsonSerializerOptions options, Type impliedType = null)
+    public static void WriteMemberBinding(this Utf8JsonWriter writer, MemberBinding value, JsonSerializerOptions options, Type? impliedType = null)
     {
         writer.WriteEnumProperty(nameof(value.BindingType), value.BindingType, options);
 
@@ -34,14 +34,14 @@ public static void WriteMemberBinding(this Utf8JsonWriter writer, MemberBinding
         }
     }
 
-    private static MemberAssignment ReadMemberAssignment(ref Utf8JsonReader reader, JsonSerializerOptions options, Type impliedType)
+    private static MemberAssignment ReadMemberAssignment(ref Utf8JsonReader reader, JsonSerializerOptions options, Type? impliedType)
     {
         var member = reader.ReadMemberInfo(options, impliedType);
         var expression = reader.ReadProperty<Expression>(nameof(MemberExpression.Expression), options);
         return Expression.Bind(member, expression);
     }
 
-    private static void WriteMemberAssignment(Utf8JsonWriter writer, JsonSerializerOptions options, MemberAssignment value, Type impliedType)
+    private static void WriteMemberAssignment(Utf8JsonWriter writer, JsonSerializerOptions options, MemberAssignment value, Type? impliedType)
     {
         writer.WriteMemberInfo(options, value.Member, impliedType);
         writer.WriteProperty(nameof(value.Expression), value.Expression, options);