Replace IFilterValueConverter with pluggable functions in filters

Author: bkoelman

benchmarks/QueryString/QueryStringParserBenchmarks.cs

@@ -41,7 +41,7 @@ public QueryStringParserBenchmarks()
         var includeReader = new IncludeQueryStringParameterReader(includeParser, request, resourceGraph);
 
         var filterScopeParser = new QueryStringParameterScopeParser();
-        var filterValueParser = new FilterParser(resourceFactory, Enumerable.Empty<IFilterValueConverter>());
+        var filterValueParser = new FilterParser(resourceFactory);
         var filterReader = new FilterQueryStringParameterReader(filterScopeParser, filterValueParser, request, resourceGraph, options);
 
         var sortScopeParser = new QueryStringParameterScopeParser();

src/JsonApiDotNetCore/Queries/Expressions/CountExpression.cs

@@ -11,6 +11,8 @@ public class CountExpression : FunctionExpression
 {
     public ResourceFieldChainExpression TargetCollection { get; }
 
+    public override Type ReturnType { get; } = typeof(int);
+
     public CountExpression(ResourceFieldChainExpression targetCollection)
     {
         ArgumentGuard.NotNull(targetCollection);

src/JsonApiDotNetCore/Queries/Expressions/FilterExpression.cs

@@ -5,4 +5,5 @@ namespace JsonApiDotNetCore.Queries.Expressions;
 /// </summary>
 public abstract class FilterExpression : FunctionExpression
 {
+    public override Type ReturnType { get; } = typeof(bool);
 }

src/JsonApiDotNetCore/Queries/Expressions/FunctionExpression.cs

@@ -5,4 +5,5 @@ namespace JsonApiDotNetCore.Queries.Expressions;
 /// </summary>
 public abstract class FunctionExpression : QueryExpression
 {
+    public abstract Type ReturnType { get; }
 }

src/JsonApiDotNetCore/Queries/Expressions/LiteralConstantExpression.cs

@@ -9,7 +9,7 @@ namespace JsonApiDotNetCore.Queries.Expressions;
 [PublicAPI]
 public class LiteralConstantExpression : IdentifierExpression
 {
-    // Only used to show the original input, in case expression parse failed. Not part of the semantic expression value.
+    // Only used to show the original input in errors and diagnostics. Not part of the semantic expression value.
     private readonly string _stringValue;
 
     public object TypedValue { get; }