Removed allocations for timestamp

Author: epeshk

src/Serilog.Expressions/Templates/Compilation/CompiledTimestampToken.cs

@@ -0,0 +1,70 @@
+// Copyright © Serilog Contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using Serilog.Expressions;
+using Serilog.Parsing;
+using Serilog.Templates.Rendering;
+using Serilog.Templates.Themes;
+
+namespace Serilog.Templates.Compilation;
+
+class CompiledTimestampToken : CompiledTemplate
+{
+    readonly string? _format;
+    readonly Alignment? _alignment;
+    readonly IFormatProvider? _formatProvider;
+    readonly Style _secondaryText;
+
+    public CompiledTimestampToken(string? format, Alignment? alignment, IFormatProvider? formatProvider, TemplateTheme theme)
+    {
+        _format = format;
+        _alignment = alignment;
+        _formatProvider = formatProvider;
+        _secondaryText = theme.GetStyle(TemplateThemeStyle.SecondaryText);
+    }
+
+    public override void Evaluate(EvaluationContext ctx, TextWriter output)
+    {
+        var invisibleCharacterCount = 0;
+
+        if (_alignment == null)
+        {
+            EvaluateUnaligned(ctx, output, _formatProvider, ref invisibleCharacterCount);
+        }
+        else
+        {
+            var writer = new StringWriter();
+            EvaluateUnaligned(ctx, writer, _formatProvider, ref invisibleCharacterCount);
+            Padding.Apply(output, writer.ToString(), _alignment.Value.Widen(invisibleCharacterCount));
+        }
+    }
+
+    void EvaluateUnaligned(EvaluationContext ctx, TextWriter output, IFormatProvider? formatProvider, ref int invisibleCharacterCount)
+    {
+        var value = ctx.LogEvent.Timestamp;
+
+        using var style = _secondaryText.Set(output, ref invisibleCharacterCount);
+
+#if FEATURE_SPAN
+        Span<char> buffer = stackalloc char[36];
+        if (value.TryFormat(buffer, out int charsWritten, _format, _formatProvider))
+        {
+            output.Write(buffer[..charsWritten]);
+            return;
+        }
+#endif
+        output.Write(value.ToString(_format, formatProvider));
+        
+    }
+}

src/Serilog.Expressions/Templates/Compilation/TemplateCompiler.cs

@@ -44,6 +44,10 @@ public static CompiledTemplate Compile(Template template,
                 Expression: AmbientNameExpression { IsBuiltIn: true, PropertyName: BuiltInProperty.Message },
                 Format: null
             } message => encoder.Wrap(new CompiledMessageToken(formatProvider, message.Alignment, theme)),
+            FormattedExpression
+            {
+                Expression: AmbientNameExpression { IsBuiltIn: true, PropertyName: BuiltInProperty.Timestamp },
+            } timestamp => encoder.Wrap(new CompiledTimestampToken(timestamp.Format, timestamp.Alignment, formatProvider, theme)),
             FormattedExpression expression => encoder.MakeCompiledFormattedExpression(
                 ExpressionCompiler.Compile(expression.Expression, formatProvider, nameResolver), expression.Format, expression.Alignment, formatProvider, theme),
             TemplateBlock block => new CompiledTemplateBlock(block.Elements.Select(e => Compile(e, formatProvider, nameResolver, theme, encoder)).ToArray()),