Add NLog instrumentation for OpenTelemetry .NET Auto-Instrumentation (#4371)

* Add NLog instrumentation for OpenTelemetry .NET Auto-Instrumentation

This commit implements a comprehensive NLog instrumentation that automatically
bridges NLog logging events to OpenTelemetry without requiring code changes.

Features:
- Automatic target injection into NLog's target collection
- Complete log event bridging with level mapping
- Structured logging support with message templates
- Trace context integration
- Custom properties forwarding with filtering
- Comprehensive test coverage
- End-to-end test application
- Extensive documentation

The implementation follows the same patterns as the existing Log4Net
instrumentation and supports NLog versions 4.0.0 through 6.*.*.

Configuration:
- OTEL_DOTNET_AUTO_LOGS_ENABLED=true
- OTEL_DOTNET_AUTO_LOGS_ENABLE_NLOG_BRIDGE=true
- OTEL_DOTNET_AUTO_LOGS_INCLUDE_FORMATTED_MESSAGE=true (optional)

Files added:
- src/OpenTelemetry.AutoInstrumentation/Instrumentations/NLog/
- test/OpenTelemetry.AutoInstrumentation.Tests/NLogTests.cs
- test/test-applications/integrations/TestApplication.NLog/

Files modified:
- Configuration classes to support NLog bridge
- Public API files to include new integration class

* Fix: #4371 (comment)

* Fix #4371 (comment): correct integration to hook into Logger.Log method

The original integration targeted a non-existent method
'GetConfiguredNamedTargets' in recent NLog versions. Changed to
intercept the actual NLog.Logger.Log(LogEventInfo) method which
is stable across NLog 4.0+ versions.

- Renamed TargetCollectionIntegration to LoggerIntegration
- Changed from OnMethodEnd to OnMethodBegin approach
- Updated public API references
- Fixes instrumentation for all NLog versions 4.0-6.*.*

* Fix: #4371 (comment) missing nlog instrumentation definition for net462

* Test: #4371 (comment). feat(nlog): add integration tests following Log4NetBridge pattern

Rework TestApplication.NLog into TestApplication.NLogBridge with proper
integration test support. Add NLogBridgeTests.cs with complete coverage
of direct NLog usage, ILogger bridge, and trace context injection.

- Add to solution and LibraryVersionsGenerator
- Fix config to remove Windows-specific paths
- Support --api nlog and --api ILogger test modes

* feat: refactor NLog instrumentation to use standard NLog Target architecture

- Replace CallTarget interception with standard NLog.Targets.TargetWithContext
- Add OpenTelemetry.AutoInstrumentation.NLogTarget project with OpenTelemetryTarget
- Implement NLogAutoInjector for zero-config auto-injection via CallTarget
- Rename OpenTelemetryNLogTarget to OpenTelemetryNLogConverter for clarity
- Update LoggerIntegration to trigger auto-injection and set GlobalDiagnosticsContext
- Rework TestApplication.NLogBridge to follow standard integration test pattern
- Update NLogBridgeTests to match Log4NetBridgeTests structure
- Add InternalsVisibleTo for new NLog target project access
- Update documentation to reflect dual-path architecture (auto-injection + manual config)
- Remove obsolete files and clean up project structure

This refactor aligns with NLog best practices by providing both automatic
instrumentation and a standard NLog Target that can be configured via
nlog.config or programmatically, leveraging NLog's native layout and
routing capabilities.

* refactor: remove unused NLog.Extensions.Logging from TestApplication.NLogBridge

The package was not referenced in any source files and the test app implements
its own ILogger bridge for testing purposes.

* refactor: optimize NLog target for async compatibility and performance

- Replace Activity.Current with Layout-based trace context resolution
- Add HasProperties check to avoid unnecessary dictionary allocation
- Remove custom Attributes property, use base class ContextProperties
- Fix parameter vs properties logic to prevent duplication
- Standardize Layout rendering patterns with RenderLogEvent
- Improve resource management with proper null handling

Enhances AsyncWrapper compatibility while reducing memory allocations
and aligning with NLog target best practices.

* feat: add hybrid typed layout support for NLog version compatibility

Implements runtime version detection to use Layout<T> for NLog 5.3.4+
while maintaining backward compatibility with NLog 4.0.0+. Eliminates
string parsing overhead on modern versions while preserving existing API.

- Add runtime NLog version detection (5.3.4+ supports typed layouts)
- Use Layout<ActivityTraceId?> and Layout<ActivitySpanId?> internally when supported
- Fall back to string parsing for older NLog versions
- Maintain public Layout? API for full backward compatibility
- Remove unnecessary LINQ conversion in GetLogEventProperties

* feat: implement NLog v5.3.4+ typed layouts for OpenTelemetryTarget

Resolves critical and high-priority issues in OpenTelemetryTarget by implementing
modern NLog typed layouts and fixing AsyncWrapper compatibility.

## Key Improvements

### Critical Issues Fixed
- **Unused Layout Properties**: TraceIdLayout and SpanIdLayout are now properly
  implemented using Layout<ActivityTraceId?> and Layout<ActivitySpanId?> with
  Layout<T>.FromMethod for optimal performance
- **AsyncWrapper Compatibility**: Fixed trace context resolution in async scenarios
  by using layout-based approach that captures context at log event creation time
- **Redundant Rendering**: Eliminated duplicate RenderLogEvent calls by rendering
  layout only once and reusing the result

### Performance Enhancements
- Implemented NLog v5.3.4+ Layout<T>.FromMethod with static lambda expressions
- Reduced memory allocations through typed layouts (eliminates boxing/parsing)
- Optimized layout rendering to avoid redundant string operations
- Added proper type safety with strongly-typed Layout<T> properties

### Code Quality
- Removed unnecessary null-forgiving operator usage
- Added comprehensive documentation explaining AsyncWrapper compatibility approach
- Updated PublicAPI definitions to reflect new typed layout signatures
- Maintained backward compatibility while leveraging modern NLog features

## Technical Details

**Before**:
- TraceIdLayout/SpanIdLayout were unused Layout? properties
- Multiple RenderLogEvent calls caused performance overhead
- AsyncWrapper scenarios lost trace context due to Activity.Current limitations

**After**:
- Typed layouts: Layout<ActivityTraceId?> and Layout<ActivitySpanId?>
- Single layout rendering with result reuse
- Layout-based trace context resolution works across async boundaries
- Static lambda expressions:

## Testing
- ✅ All unit tests pass (31/31)
- ✅ Project builds without errors or warnings
- ✅ PublicAPI validation passes
- ✅ No linter errors

Closes: Critical and high findings in OpenTelemetryTarget code review

* fix test coverage

* fix: correct NLog bridge EmitLog method call to match OpenTelemetry SDK

- Change EmitLogRecord to EmitLog method name
- Use ref parameter types with MakeByRefType()
- Add explicit BindingFlags for method resolution
- Align with Log4Net bridge implementation

Fixes NLog bridge initialization failures due to method not found errors.

* refactor: simplify NLog target configuration to use environment variables only

- Remove all programmatic configuration properties from OpenTelemetryTarget
- Simplify OTLP exporter setup to use standard environment variables
- Use reasonable defaults for message formatting and parameter inclusion
- Update documentation to reflect environment-only configuration
- Maintain all existing functionality while eliminating assembly loading risks

* Removed NLog from AssemblyInfo

* feat: add NLog instrumentation with duck typing and NLog 6.x support

- Add NLog logs instrumentation for versions 5.0+ and 6.x
- Use duck typing for zero-config auto-injection without assembly references
- Configure via OpenTelemetry environment variables only
- Update CHANGELOG.md and config.md documentation
- Add NLog 6.0.0 to test matrix for broader version coverage

* fix CHANGELOG

* Fix build errors

* commit generated file

* Move NLog version to test folder

* cleanup solution

* add NLOG to dictionary

* typo fixes

* remove reference to NLog.Extensions.Logging

it is not used

* Update tested versions

* Minimal assembly version set to 4.0.0

There is no tests for these versions

* fix sln file

* remove reference to System.Private.Uri

seems to be redundant

* Fix compilation for tests app

* Apply suggestions from code review

* Fix issue occurring in VS

* Add missing settings test case

* remove redundant lines

* Sync implementation with available documentation

* user facing documentation

* refactor: Switch NLog integration from target injection to bytecode interception

Replace target-based approach with direct Logger.Log() interception using duck typing.
Remove OpenTelemetryTarget and NLogAutoInjector, update LoggerProvider initialization,
and add comprehensive test coverage for all log levels including Trace/Debug.

* fix: resolve kielek feedback about injecting trace context even when nlog bridge is disabled

* refactor(nlog): target WriteToTargets instead of Logger.Log

Intercept WriteToTargets/WriteLogEventToTargets to capture all log
events including convenience methods (log.Info, log.Debug, etc).

- Add WriteToTargetsIntegration for NLog 5.3.0+
- Add WriteToTargetsLegacyIntegration for NLog 5.0.0-5.2.x
- Add WriteLogEventToTargetsIntegration for NLog 6.x
- Add NLogIntegrationHelper to share logic
- Remove LoggerIntegration (only caught explicit Logger.Log calls)

* fix(nlog): correct log record attribute handling

- Use RecordException for proper exception attributes
- Remove "arg_" prefix from parameter keys
- Add GlobalDiagnosticsContext property capture
- Remove unused import

* test(nlog): update tests for new instrumentation approach

- Fix trace context injection test regex
- Expect "Information" for ILogger bridge
- Add GlobalDiagnosticsContext test property
- Add trace context to nlog.config layout

* docs(nlog): update README for new architecture

* refactor(nlog): remove GlobalDiagnosticsContext integration

GDC is for static application-wide properties set at startup.
OpenTelemetry has its own enrichment for service metadata.

* fix: remove duplicate package versions in Directory.Packages.props

* fix(nlog): support .NET Framework expression tree limitations

Assign log record and attributes to local variables before passing
to EmitLog method with ref parameters. .NET Framework's expression
tree compiler doesn't support TryExpression nested in ref parameter
method calls.

* fix: removed duplicates from the unshipped api

* Fix changelog place

* generated files

* Bump NLog to 6.0.6

* Comments why we need more library versions in the coverage

* Fix NLog trace context injection test

* Add longdate to spellcheck dictionary

* Fix regex to handle 12-hour time format

* Fix duplicate NET472 in NetFramework array

* Fix NLog trace context test regex for macOS locale

macOS uses narrow no-break space (U+202F) between time and AM/PM,
not regular ASCII space. Use \s* to match any Unicode whitespace.

* File based configuration

* cleanup test application

* Modern array initialization

* Add NLog integrations for wrapperType overload

Cover Logger.Log(Type wrapperType, LogEventInfo logEvent) API:
- WriteLogEventToTargetsWithWrapperTypeIntegration for NLog 6.x
- WriteToTargetsWithWrapperTypeIntegration for NLog 5.3.0+
- WriteToTargetsWithWrapperTypeLegacyIntegration for NLog 5.0.0-5.2.x

* Remove unused IMessageTemplateParameters interface

* Use official NLog.Extensions.Logging package

Replace custom NLogLoggerProvider with official NLog.Extensions.Logging
package for ILogger integration testing.

* Fix ClrNames.Type reference and SA1518 error

- Use "System.Type" string instead of non-existent ClrNames.Type
- Fix trailing newline in ILoggingEvent.cs

* Consolidate NLog integrations from 6 files to 2

Use multiple [InstrumentMethod] attributes per class:
- NLogWriteToTargetsIntegration: 2-param methods (3 attributes)
- NLogWriteToTargetsWithWrapperTypeIntegration: 3-param methods (3 attributes)

* generated file

* Centos SHA update

* lint check

* Add test coverage for Logger.Log(Type wrapperType, LogEventInfo) overload

- Add LogWithWrapperType method to test application to exercise 3-parameter
  WriteToTargets/WriteLogEventToTargets instrumentation
- Add test expectation for wrapperType log message in NLogBridgeTests
- Add NLog.Extensions.Logging to central package management
- Update AssertStandardOutputExpectations to verify wrapperType message

* Fix build after merge with main

* Improve managing tests dependencies

* Fig merge main issue

---------

Co-authored-by: Piotr Kiełkowicz <pkiekowicz@splunk.com>
Co-authored-by: Mateusz Łach <mateusza@splunk.com>

Author: 3 people

.cspell/other.txt

@@ -29,6 +29,7 @@ ILOGGER
 inetsrv
 JIT
 LINQ
+longdate
 MASSTRANSIT
 metricsexporter
 mkdir
@@ -41,6 +42,7 @@ mycompanymyproductmylibrary
 MYSQLCONNECTOR
 MYSQLDATA
 NETRUNTIME
+NLOG
 Npgsql
 NSERVICEBUS
 omnisharp

CHANGELOG.md

@@ -11,6 +11,9 @@ This component adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.h
 
 - Add `-NoReset` switch parameter to skip service restart in PowerShell
   registration functions.
+- Support for [`NLog`](https://www.nuget.org/packages/NLog/)
+  logs instrumentation for versions `5.*` and `6.*` on .NET using duck typing
+  for zero-config auto-injection.
 
 ### Changed
 

OpenTelemetry.AutoInstrumentation.sln

@@ -246,6 +246,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SdkVersionAnalyzer", "tools
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestApplication.Log4NetBridge", "test\test-applications\integrations\TestApplication.Log4NetBridge\TestApplication.Log4NetBridge.csproj", "{926B7C03-42C2-4192-94A7-CD0B1C693279}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestApplication.NLogBridge", "test\test-applications\integrations\TestApplication.NLogBridge\TestApplication.NLogBridge.csproj", "{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}"
+EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestApplication.SelectiveSampler", "test\test-applications\integrations\TestApplication.SelectiveSampler\TestApplication.SelectiveSampler.csproj", "{FD1A1ABD-6A48-4E94-B5F7-2081AFCD1BBB}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestApplication.ProfilerSpanStoppageHandling", "test\test-applications\integrations\TestApplication.ProfilerSpanStoppageHandling\TestApplication.ProfilerSpanStoppageHandling.csproj", "{665280EB-F428-4C04-A293-33228C73BF8A}"
@@ -1538,6 +1540,22 @@ Global
 		{926B7C03-42C2-4192-94A7-CD0B1C693279}.Release|x64.Build.0 = Release|x64
 		{926B7C03-42C2-4192-94A7-CD0B1C693279}.Release|x86.ActiveCfg = Release|x86
 		{926B7C03-42C2-4192-94A7-CD0B1C693279}.Release|x86.Build.0 = Release|x86
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Debug|Any CPU.ActiveCfg = Debug|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Debug|Any CPU.Build.0 = Debug|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Debug|ARM64.ActiveCfg = Debug|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Debug|ARM64.Build.0 = Debug|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Debug|x64.ActiveCfg = Debug|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Debug|x64.Build.0 = Debug|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Debug|x86.ActiveCfg = Debug|x86
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Debug|x86.Build.0 = Debug|x86
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Release|Any CPU.ActiveCfg = Release|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Release|Any CPU.Build.0 = Release|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Release|ARM64.ActiveCfg = Release|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Release|ARM64.Build.0 = Release|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Release|x64.ActiveCfg = Release|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Release|x64.Build.0 = Release|x64
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Release|x86.ActiveCfg = Release|x86
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D}.Release|x86.Build.0 = Release|x86
 		{FD1A1ABD-6A48-4E94-B5F7-2081AFCD1BBB}.Debug|Any CPU.ActiveCfg = Debug|x64
 		{FD1A1ABD-6A48-4E94-B5F7-2081AFCD1BBB}.Debug|Any CPU.Build.0 = Debug|x64
 		{FD1A1ABD-6A48-4E94-B5F7-2081AFCD1BBB}.Debug|ARM64.ActiveCfg = Debug|x64
@@ -1692,6 +1710,7 @@ Global
 		{AA3E0C5C-A4E2-46AB-BD18-2D30D3ABF692} = {E409ADD3-9574-465C-AB09-4324D205CC7C}
 		{C75FA076-D460-414B-97F7-6F8D0E85AE74} = {00F4C92D-6652-4BD8-A334-B35D3E711BE6}
 		{926B7C03-42C2-4192-94A7-CD0B1C693279} = {E409ADD3-9574-465C-AB09-4324D205CC7C}
+		{A7B8C9D0-1E2F-3A4B-5C6D-7E8F9A0B1C2D} = {E409ADD3-9574-465C-AB09-4324D205CC7C}
 		{FD1A1ABD-6A48-4E94-B5F7-2081AFCD1BBB} = {E409ADD3-9574-465C-AB09-4324D205CC7C}
 		{665280EB-F428-4C04-A293-33228C73BF8A} = {E409ADD3-9574-465C-AB09-4324D205CC7C}
 		{500BF40F-EECB-4F6A-377B-EDBDFFDE09BE} = {E409ADD3-9574-465C-AB09-4324D205CC7C}

build/LibraryVersions.g.cs

@@ -68,6 +68,15 @@ public static partial class LibraryVersion
                 new("3.2.0"),
             ]
         },
+        {
+            "TestApplication.NLogBridge",
+            [
+                new("5.0.0", additionalMetaData: new() { { "NLogExtensionsLogging", "5.0.0" } }),
+                new("5.3.4", additionalMetaData: new() { { "NLogExtensionsLogging", "5.3.15" } }),
+                new("6.0.0", additionalMetaData: new() { { "NLogExtensionsLogging", "6.0.0" } }),
+                new("6.0.6", additionalMetaData: new() { { "NLogExtensionsLogging", "6.1.0" } }),
+            ]
+        },
         {
             "TestApplication.MassTransit",
             [

build/TargetFramework.cs

@@ -19,7 +19,7 @@ public class TargetFramework : Enumeration
 
     // should be in version order
     public static readonly TargetFramework[] NetFramework = {
-        NET462, NET47, NET471, NET472, NET472
+        NET462, NET47, NET471, NET472
     };
 
     public static implicit operator string(TargetFramework framework)

docs/config.md

@@ -206,6 +206,7 @@ due to lack of stable semantic convention.
 |-----------|---------------------------------------------------------------------------------------------------------------------------------|--------------------|--------------------------|-----------------------------------------------------------------------------------------------------------------------------------|
 | `ILOGGER` | [Microsoft.Extensions.Logging](https://www.nuget.org/packages/Microsoft.Extensions.Logging) **Not supported on .NET Framework** | ≥8.0.0             | bytecode or source \[1\] | [Experimental](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/versioning-and-stability.md) |
 | `LOG4NET` | [log4net](https://www.nuget.org/packages/log4net) \[2\]                                                                         | ≥2.0.13 && < 4.0.0 | bytecode                 | [Experimental](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/versioning-and-stability.md) |
+| `NLOG`    | [NLog](https://www.nuget.org/packages/NLog) \[3\]                                                                               | ≥5.0.0 && < 7.0.0  | bytecode                 | [Experimental](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/versioning-and-stability.md) |
 
 \[1\]: For ASP.NET Core applications, the `LoggingBuilder` instrumentation
 can be enabled without using the .NET CLR Profiler by setting
@@ -215,6 +216,9 @@ the `ASPNETCORE_HOSTINGSTARTUPASSEMBLIES` environment variable to
 \[2\]: Instrumentation provides both [trace context injection](./log-trace-correlation.md#log4net-trace-context-injection)
 and [logs bridge](./log4net-bridge.md).
 
+\[3\]:  Instrumentation provides both [trace context injection](./log-trace-correlation.md#log4net-trace-context-injection)
+and [logs bridge](./nlog-bridge.md).
+
 ### Instrumentation options
 
 | Environment variable                                                              | Description                                                                                                                                                                                                                              | Default value | Status                                                                                                                            |

docs/file-based-configuration.md

@@ -526,6 +526,7 @@ instrumentation/development:
     logs:
       ilogger:             # Microsoft.Extensions.Logging
       log4net:             # Log4Net
+      nlog:                # NLog
 ```
 
 ## Instrumentation options
@@ -567,6 +568,10 @@ instrumentation/development:
         # Logs bridge is disabled by default
         # More info about log4net bridge can be found at https://github.com/open-telemetry/opentelemetry-dotnet-instrumentation/blob/main/docs/log4net-bridge.md
         bridge_enabled: true
+      nlog:
+        # Logs bridge is disabled by default
+        # More info about NLog bridge can be found at https://github.com/open-telemetry/opentelemetry-dotnet-instrumentation/blob/main/docs/nlog-bridge.md
+        bridge_enabled: true
 ```
 
 ## Instrumentation Additional Sources

docs/log-trace-correlation.md

@@ -62,3 +62,27 @@ Following properties are set by default on the collection of logging event's pro
 
 This allows for trace context to be logged into currently configured log destination,
  e.g. a file. In order to use them, pattern needs to be updated.
+
+### `NLog`
+
+See [`nlog-bridge`](./nlog-bridge.md).
+
+## `NLog` trace context injection
+
+> [!IMPORTANT]
+> NLog trace context injection is an experimental feature.
+
+The `NLog` trace context injection is enabled by default.
+It can be disabled by setting
+`OTEL_DOTNET_AUTO_LOGS_NLOG_INSTRUMENTATION_ENABLED` to `false`.
+
+Context injection is supported for `NLOG` in versions >= 5.0.0 && < 7.0.0
+
+Following properties are set by default on the collection of logging event's properties:
+
+- `trace_id`
+- `span_id`
+- `trace_flags`
+
+This allows for trace context to be logged into currently configured log destination,
+ e.g. a file. In order to use them, pattern needs to be updated.

docs/nlog-bridge.md

@@ -0,0 +1,45 @@
+# `NLog` [logs bridge](https://opentelemetry.io/docs/specs/otel/glossary/#log-appender--bridge)
+
+> [!IMPORTANT]
+> NLog bridge is an experimental feature.
+
+The `NLog` logs bridge is disabled by default. In order to enable it,
+set `OTEL_DOTNET_AUTO_LOGS_ENABLE_NLOG_BRIDGE` to `true`.
+
+Bridge is supported for `NLOG` in versions >= 5.0.0 && < 7.0.0
+
+If `NLOG` is used as a [logging provider](https://learn.microsoft.com/en-us/dotnet/core/extensions/logging-providers),
+`NLOG` bridge should not be enabled, in order to reduce possibility of
+duplicated logs export.
+
+## `NLog` logging events conversion
+
+`NLog`'s `ILoggingEvent`s are converted to OpenTelemetry log records in
+a following way:
+
+- `TimeStamp` is set as a `Timestamp`
+- `Level.Name` is set as a `SeverityText`
+- `FormattedMessage` is set as a `Body` if it is available
+- Otherwise, `Message` is set as a `Body`
+- `LoggerName` is set as an `InstrumentationScope.Name`
+- `GetProperties()`, apart from builtin properties prefixed with `nlog:`, `NLog.`,
+  are added as attributes
+- `Exception` is used to populate the following properties: `exception.type`,
+  `exception.message`, `exception.stacktrace`
+- `Level.Value` is mapped to `SeverityNumber` as outlined in the next section
+
+### `NLog` level severity mapping
+
+`NLog` levels are mapped to OpenTelemetry severity types according to
+ following rules based on their numerical values.
+
+Levels with numerical values of:
+
+- Equal to `LogLevel.Fatal` is mapped to `LogRecordSeverity.Fatal`
+- Equal to `LogLevel.Error` is mapped to `LogRecordSeverity.Error`
+- Equal to `LogLevel.Warn` is mapped to `LogRecordSeverity.Warn`
+- Equal to `LogLevel.Info` is mapped to `LogRecordSeverity.Info`
+- Equal to `LogLevel.Debug` is mapped to `LogRecordSeverity.Debug`
+- Equal to `LogLevel.Trace` is mapped to `LogRecordSeverity.Trace`
+- Equal to `LogLevel.Off` is mapped to `LogRecordSeverity.Trace`
+- Any other is mapped to `LogRecordSeverity.Info`.

src/OpenTelemetry.AutoInstrumentation/.publicApi/net462/PublicAPI.Unshipped.txt

@@ -1 +1,2 @@
-
+OpenTelemetry.AutoInstrumentation.Instrumentations.NLog.TraceContextInjection.Integrations.NLogWriteToTargetsIntegration
+OpenTelemetry.AutoInstrumentation.Instrumentations.NLog.TraceContextInjection.Integrations.NLogWriteToTargetsWithWrapperTypeIntegration