feat: Add property-argument highlighting for Serilog templates (#17)

Highlights the connection between template properties and their corresponding arguments when cursor is on either. Pressing ESC dismisses highlights.

- Highlights both property and argument when cursor is on either one
- Supports all string formats (regular, verbatim, raw strings)
- Handles special cases (LogError exceptions, positional parameters, anonymous objects)
- Excludes ExpressionTemplate contexts where properties have no arguments

Author: willibrandon

CLAUDE.md

@@ -157,6 +157,7 @@ This extension provides syntax highlighting and navigation for Serilog message t
 - **Syntax highlighting** for Serilog.Expressions filter syntax and expression templates
 - **Navigation** support (Go to Definition) between template properties and arguments
 - **Brace matching** for template property delimiters and expression templates
+- **Property-argument highlighting** shows connections between properties and arguments on cursor position
 
 ### Technical Stack
 - **Roslyn Classification API** - For syntax highlighting via `IClassifier`
@@ -194,14 +195,15 @@ The extension includes these components:
 3. **Classification/SerilogClassifierProvider.cs** - MEF export for classifier
 4. **Navigation/SerilogNavigationProvider.cs** - Navigation from properties to arguments via light bulb
 5. **Tagging/SerilogBraceMatcher.cs** - Implements `ITagger<TextMarkerTag>` for brace matching
-6. **Utilities/SerilogCallDetector.cs** - Centralized Serilog call detection logic
-7. **Utilities/LruCache.cs** - Thread-safe LRU cache for parsed templates
+6. **Tagging/PropertyArgumentHighlighter.cs** - Implements `ITagger<TextMarkerTag>` for property-argument highlighting
+7. **Utilities/SerilogCallDetector.cs** - Centralized Serilog call detection logic
+8. **Utilities/LruCache.cs** - Thread-safe LRU cache for parsed templates
 
 #### Serilog.Expressions Support
-8. **Expressions/ExpressionTokenizer.cs** - Tokenizes Serilog.Expressions syntax
-9. **Expressions/ExpressionParser.cs** - Parses expressions and templates into classified regions
-10. **Expressions/ExpressionDetector.cs** - Detects expression contexts (filter, template, etc.)
-11. **Classification/SyntaxTreeAnalyzer.cs** - Roslyn-based analysis for expression contexts
+9. **Expressions/ExpressionTokenizer.cs** - Tokenizes Serilog.Expressions syntax
+10. **Expressions/ExpressionParser.cs** - Parses expressions and templates into classified regions
+11. **Expressions/ExpressionDetector.cs** - Detects expression contexts (filter, template, etc.)
+12. **Classification/SyntaxTreeAnalyzer.cs** - Roslyn-based analysis for expression contexts
 
 ### Performance Considerations
 - LRU cache for parsed templates (10x improvement for repeated templates)

Example/ExampleService.cs

@@ -2,7 +2,7 @@
 
 public class ExampleService(ILogger<ExampleService> logger)
 {
-    private static readonly string[] consoleLoggerScopes = [nameof(RunExamplesAsync), nameof(ConsoleLoggerEmulationExample)];
+    private static readonly string[] ConsoleLoggerScopes = [nameof(RunExamplesAsync), nameof(ConsoleLoggerEmulationExample)];
 
     public async Task RunExamplesAsync()
     {
@@ -512,7 +512,7 @@ private async Task ConsoleLoggerEmulationExample()
         program.Information("Host listening at {ListenUri}", "https://hello-world.local");
 
         program
-            .ForContext("Scope", consoleLoggerScopes)
+            .ForContext("Scope", ConsoleLoggerScopes)
             .Information("HTTP {Method} {Path} responded {StatusCode} in {Elapsed:0.000} ms", "GET", "/api/hello", 200, 1.23);
 
         program.Warning("We've reached the end of the line");

Example/README.md

@@ -91,6 +91,7 @@ Open `Program.cs` in Visual Studio with the Serilog Syntax extension installed t
 ### Interactive Features
 - **Brace matching** when cursor is on `{` or `}`
 - **Light bulb navigation** from properties to arguments
+- **Property-argument highlighting** when cursor is on either a property or argument
 - **Immediate highlighting** as you type (before closing quotes)
 - **Multi-line support** for verbatim and raw strings
 

README.md

@@ -49,6 +49,13 @@ A Visual Studio 2022 extension that provides syntax highlighting, brace matching
 - **Navigate to argument** - jump from template properties to their corresponding arguments
 - Click the light bulb and select "Navigate to 'PropertyName' argument"
 
+### 🔦 Property-Argument Highlighting
+- **Interactive highlighting** of property-argument connections
+- When cursor is on a template property (e.g., `{UserId}`), both the property and its corresponding argument are highlighted
+- When cursor is on an argument, both the argument and its template property are highlighted
+- Works across all string literal types (regular, verbatim `@"..."`, raw `"""..."""`)
+- Supports complex scenarios including multi-line templates, collection expressions, and LogError with exception parameters
+
 ### 🔍 Brace Matching
 - Highlight matching braces when cursor is positioned on `{` or `}`
 - Visual indication of brace pairs in complex templates
@@ -246,6 +253,7 @@ Key components:
 - `SerilogClassifier` - Handles syntax highlighting with smart cache invalidation
 - `SerilogBraceMatcher` - Provides brace matching
 - `SerilogNavigationProvider` - Enables property-to-argument navigation
+- `PropertyArgumentHighlighter` - Highlights property-argument connections on cursor position
 - `SerilogCallDetector` - Optimized Serilog call detection with pre-check optimization
 - `SerilogThemeColors` - Theme-aware color management with WCAG AA compliance
 - `TemplateParser` - Parses Serilog message templates