Diagnostics

Diagnostics

The package ships a single Roslyn analyzer, TelemetryDiagnosticAnalyzer, which validates telemetry interfaces and raises diagnostics with the TSG prefix. All diagnostics are grouped by category.

Note

Each rule is also tracked for release purposes in AnalyzerReleases.Shipped.md and AnalyzerReleases.Unshipped.md, which carry the rule ID, category, and severity and are validated by the Roslyn release-tracking analyzers on every build.

• General — TSG1xxx
• Logging — TSG2xxx
• Activities — TSG3xxx
• Metrics — TSG4xxx

General diagnostics (TSG1xxx)

ID	Severity	Description
TSG1000	Error	Fatal execution error occurred (Failed to execute the generation stage: {0}). Raised by the generator itself when an unexpected exception escapes the pipeline.
TSG1001	Error	Inferring generation targets is not supported when using multi-target generation. A method on a multi-target interface has no explicit generation attribute.
TSG1002	Error	Multiple attributes from the same target family are not supported. Only one Activity, Logging, or Metrics attribute is allowed per method.
TSG1003	Error	Duplicate method names are not supported. Two or more methods on the interface share the same name.
TSG1004	Error	Generic interfaces are not supported.
TSG1005	Error	Generic methods are not supported.
TSG1006	Warning	ExcludeTargets references a target not present on this method.
TSG1007	Warning	ExcludeTargets results in an empty or invalid parameter set for a target.
TSG1008	Warning	Activity parameter has no Activity target. A parameter of type Activity is present on a method with no [Activity]/[Event]/[Context] attribute.
TSG1010	Error	Method target not registered on interface. A method carries an attribute for a target family that is not registered on the interface.
TSG1011	Error	Unsupported target framework. The compilation targets neither .NET 8+ nor .NET Framework 4.8+ (for example netstandard2.0), so no telemetry is generated for it. There is no opt-out. Target net8.0 or later, or net48 or later; a multi-targeted library references the package only from its supported targets (a Condition on the PackageReference), with the telemetry interfaces under the same condition. See Platform Support.

Logging diagnostics (TSG2xxx)

ID	Severity	Description
TSG2000	Error	Too many exception parameters. A non-scoped log method has more than one Exception-typed parameter.
TSG2001	Error	More than 6 parameters. A log method in v1 generation mode has more than 6 non-exception parameters.
TSG2002	Info	Inferring error log level. In v1 generation, a single Exception parameter is present with no explicit level, so Error is inferred.
TSG2003	Warning	Could not find a reference to Microsoft.Extensions.Logging.ILogger, skipping log generation.
TSG2004	Error	Cannot mix ordinal and named property placeholders in a message template.
TSG2005	Error	Ordinal values exceed parameter count. The maximum ordinal placeholder value exceeds the number of provided parameters.
TSG2006	Error	Using [LogProperties] and [ExpandEnumerable] on the same parameter is not supported.
TSG2007	Warning	A scoped log shouldn’t have a LogLevel; it will be ignored.
TSG2008	Warning	Unbounded enumeration possible. [ExpandEnumerable] has a MaximumValueCount greater than the recommended default of 5.
TSG2021	Error	Log method must return void or IDisposable. (Returning Activity is allowed when the method is also an Activity method.)

Activities diagnostics (TSG3xxx)

ID	Severity	Description
TSG3000	Warning	Baggage parameter types only accept strings (ToString() will be called).
TSG3001	Warning	No activity source specified. Generation defaults to purview when no name is available anywhere.
TSG3002	Error	Invalid return type. An Activity/Event method returns something other than void or System.Diagnostics.Activity.
TSG3003	Error	Duplicate reserved parameters defined. More than one parameter maps to the same reserved destination.
TSG3004	Error	Activity parameter is not valid. An Activity-destination parameter appears on an Activity method (only valid on [Event] methods).
TSG3005	Error	Timestamp parameter is not valid. A timestamp parameter appears on a method that is not an [Event] method.
TSG3006	Error	Start time parameter is not valid on Create activity or Event method.
TSG3007	Error	Parent context or Parent Id parameter is not valid on event.
TSG3008	Error	Activity links parameters are not valid on events or context methods.
TSG3009	Error	Activity tags parameter is not valid on context methods.
TSG3010	Error	Escaped parameters must be a boolean.
TSG3011	Error	Escaped parameters are only valid on Events, not Activity or Context methods.
TSG3012	Info	There are no Activity methods defined, assumed use of Activity.Current.
TSG3013	Warning	Should return the created Activity. An Activity method does not return the created Activity.
TSG3014	Warning	Should accept an Activity to apply the Event/Tags/Baggage to. An Event/Context method has no Activity parameter. Opt-in via ActivitySourceGeneration.GenerateDiagnosticsForMissingActivity (default true).
TSG3015	Info	Activity should be the first parameter. Opt-in via GenerateDiagnosticsForMissingActivity.
TSG3016	Error	Status description parameter should be a string.
TSG3017	Error	Status Description parameters are only valid on Events, not Activity or Context methods.
TSG3021	Info	Exception event does not use OpenTelemetry standard name. An [Event] method records an exception under the OpenTelemetry exception rules but the event name is not the standard "exception" (suggest [Event(Name = "exception")]). Not raised when UseRecordExceptionRules is disabled, for [Baggage] exceptions, or when the exception parameter is excluded from the Activities target.
TSG3022	Warning	Activity return type should be nullable. An Activity method returns non-nullable Activity; use Activity? because the Activity can be null when no listeners are active.
TSG3023	Warning	ActivitySourceFactory is not available. UseActivitySourceFactory is set but System.Diagnostics.ActivitySourceFactory (.NET 11, or System.Diagnostics.DiagnosticSource 11+) cannot be resolved; a static ActivitySource is generated instead.

Metrics diagnostics (TSG4xxx)

ID	Severity	Description
TSG4000	Error	No instrument defined. A method on a Metrics interface has no instrument attribute and is not excluded.
TSG4001	Error	Must return void or bool. A metrics-owned method returns something other than void or bool.
TSG4002	Error	Auto increment counter and measurement defined. An auto-increment instrument also has a measurement parameter.
TSG4003	Error	Multiple measurement values defined.
TSG4004	Error	No measurement value defined. A non-auto-increment instrument method has no measurement parameter.
TSG4005	Error	Observable instrument requires Func<T>.
TSG4006	Error	Invalid measurement type. Not one of byte, short, int, long, double, float, decimal, Measurement<T>, or IEnumerable<Measurement<T>>.
TSG4007	Error	Observable metrics cannot return bool.
TSG4008	Error	AutoCounter must return void.
TSG4009	Warning	Instrument name matches the instrument type name. Use a name that describes what is measured.

Common resolutions

TSG1001 — inference disabled on multi-target interfaces

A method on a multi-target interface ([ActivitySource] + [Logger] + [Meter]) has no explicit attribute. Add the attributes for each target the method should emit, or mark it [Exclude].

[ActivitySource("MyApp")]
[Logger]
[Meter]
interface IMyTelemetry
{
    [Info]      // ✅ explicit target
    void ProcessItem(int id);
}

TSG1003 — duplicate method names

Two or more methods share the same name, which is used to generate members on the implementation class. Rename the methods.

TSG2008 — unbounded enumeration

[ExpandEnumerable] is configured with a MaximumValueCount greater than 5. Reduce it to the recommended default (5) unless you have tested the performance impact.

TSG3013 / TSG3014 — missing Activity

An Activity method does not return the created Activity, or an Event/Context method has no Activity parameter. Return the Activity/Activity? and pass it to Event/Context methods. These best-practice diagnostics are controlled by ActivitySourceGeneration.GenerateDiagnosticsForMissingActivity.

TSG3021 — exception event name

Rename the event with [Event(Name = "exception")] so the OpenTelemetry exception tags (exception.type, exception.message, exception.stacktrace, exception.escaped) are attached to that event instead of a separate event named exception.

[Event(Name = "exception")]                       // ✅ the event carries the exception tags
void FailedToRetrieve(Activity? activity, Exception exception);

A Name set on a logging attribute does not name the event — it renames the log entry:

[Event]                                           // ❌ event name is the method name
[Error(Name = "exception")]                       // the log entry is named 'exception'
void FailedToRetrieve(Activity? activity, Exception exception);

The diagnostic is not raised when the exception is not recorded using the OpenTelemetry exception rules: [Event(UseRecordExceptionRules = false)], a [Baggage] exception parameter, or an exception parameter excluded from the Activities target ([ExcludeTargets(Targets.Activities)]).

TSG3022 — non-nullable Activity return

Return Activity? so callers can handle the null case when no listeners are active.

TSG3023 — ActivitySourceFactory is not available

[assembly: ActivitySourceGeneration(..., UseActivitySourceFactory = true)] asks for sources created by System.Diagnostics.ActivitySourceFactory, but the compilation cannot resolve that type, so a static ActivitySource is generated instead. Target net11.0, or reference System.Diagnostics.DiagnosticSource 11 or later; or remove the option. See Creating sources with ActivitySourceFactory.

TSG4002 — auto-increment counter with a measurement

[AutoCounter] (or [Counter(AutoIncrement = true)]) must not declare a measurement parameter — the measurement is fixed to 1.

See also

• Getting Started
• Activities, Logging, Metrics
• Multi-Targeting