Simplify expression compilation

Author: nblumhardt

src/Serilog.Expressions/Expressions/Compilation/Linq/Intrinsics.cs

@@ -0,0 +1,65 @@
+using System.Linq;
+using System.Text.RegularExpressions;
+using Serilog.Events;
+using Serilog.Expressions.Runtime;
+
+namespace Serilog.Expressions.Compilation.Linq
+{
+    static class Intrinsics
+    {
+        static readonly LogEventPropertyValue NegativeOne = new ScalarValue(-1);
+        
+        public static LogEventPropertyValue ConstructSequenceValue(LogEventPropertyValue[] elements)
+        {
+            // Avoid upsetting Serilog's (currently) fragile `SequenceValue.Render()`.
+            if (elements.Any(el => el == null))
+                return null;
+            return new SequenceValue(elements);
+        }
+        
+        public static bool CoerceToScalarBoolean(LogEventPropertyValue value)
+        {
+            if (value is ScalarValue sv && sv.Value is bool b)
+                return b;
+            return false;
+        }
+        
+        public static LogEventPropertyValue IndexOfMatch(LogEventPropertyValue value, Regex regex)
+        {
+            if (value is ScalarValue scalar &&
+                scalar.Value is string s)
+            {
+                var m = regex.Match(s);
+                if (m.Success)
+                    return new ScalarValue(m.Index);
+                return NegativeOne;
+            }
+
+            return null;
+        }
+
+        public static LogEventPropertyValue GetPropertyValue(LogEvent context, string propertyName)
+        {
+            if (!context.Properties.TryGetValue(propertyName, out var value))
+                return null;
+
+            return value;
+        }
+
+        public static LogEventPropertyValue TryGetStructurePropertyValue(LogEventPropertyValue maybeStructure, string name)
+        {
+            if (maybeStructure is StructureValue sv)
+            {
+                foreach (var prop in sv.Properties)
+                {
+                    if (prop.Name == name)
+                    {
+                        return prop.Value;
+                    }
+                }
+            }
+
+            return null;
+        }
+    }
+}