Use CLEF names for built-in properties

Author: nblumhardt

example/Sample/Program.cs

@@ -5,13 +5,14 @@
 
 namespace Sample
 {
+    // ReSharper disable once ClassNeverInstantiated.Global
     public class Program
     {
         public static void Main()
         {
             SelfLog.Enable(Console.Error);
 
-            const string expr = "@Level = 'Information' and AppId is not null and Items[?] like 'C%'";
+            const string expr = "@l = 'Information' and AppId is not null and Items[?] like 'C%'";
 
             using var log = new LoggerConfiguration()
                 .Enrich.WithProperty("AppId", 10)
@@ -21,7 +22,7 @@ public static void Main()
                 .WriteTo.Console(outputTemplate:
                     "[{Timestamp:HH:mm:ss} {Level:u3} ({SourceContext})] {Message:lj} (first item is {FirstItem}){NewLine}{Exception}")
                 .WriteTo.Console(new OutputTemplate(
-                    "[{@Timestamp} {@Level} ({SourceContext})] {@Message} (first item is {Items[0]})\n{@Exception}"))
+                    "[{@t} {@l} ({SourceContext})] {@m} (first item is {Items[0]})\n{@x}"))
                     .CreateLogger();
 
             log.ForContext<Program>().Information("Cart contains {@Items}", new[] { "Tea", "Coffee" });

src/Serilog.Expressions/Expressions/BuiltInProperty.cs

@@ -2,12 +2,14 @@ namespace Serilog.Expressions
 {
     static class BuiltInProperty
     {
-        public const string Exception = "Exception";
-        public const string Level = "Level";
-        public const string Timestamp = "Timestamp";
-        public const string Message = "Message";
-        public const string MessageTemplate = "MessageTemplate";
-        public const string Properties = "Properties";
+        public const string Exception = "x";
+        public const string Level = "l";
+        public const string Timestamp = "t";
+        public const string Message = "m";
+        public const string MessageTemplate = "mt";
+        public const string Properties = "p";
+        
+        // Undocumented, simplifies a few scenarios; an `undefined()` may be better.
         public const string Undefined = "Undefined";
     }
 }

test/Serilog.Expressions.Tests/Cases/template-evaluation-cases.asv

@@ -1,3 +1,5 @@
 // Temporarily using Serilog's default value formatting
-Hello, {'world'}!                        ⇶ Hello, "world"!
-{@Level}                                 ⇶ "Information"
+Hello, {'world'}!                        ⇶ Hello, world!
+{@l}                                     ⇶ Information
+Items are {[1, 2]}                       ⇶ Items are [1,2]
+{@p}                                     ⇶ {}

test/Serilog.Expressions.Tests/ExpressionCompilerTests.cs

@@ -78,7 +78,7 @@ public void ExpressionsEvaluateWildcardsOnCollectionItems()
         [Fact]
         public void ExpressionsEvaluateBuiltInProperties()
         {
-            AssertEvaluation("@Level = 'Information'",
+            AssertEvaluation("@l = 'Information'",
                 Some.InformationEvent(),
                 Some.WarningEvent());
         }
@@ -121,7 +121,7 @@ public void SequenceLengthCanBeDetermined()
         [Fact]
         public void InMatchesLiterals()
         {
-            AssertEvaluation("@Level in ['Warning', 'Error']",
+            AssertEvaluation("@l in ['Warning', 'Error']",
                 Some.LogEvent(LogEventLevel.Error, "Hello"),
                 Some.InformationEvent("Hello"));
         }