Diagnostics Reference

Diagnostics Reference

This page lists all diagnostic codes emitted by the Purview Telemetry Source Generator with their severity levels, categories, and descriptions.

Understanding Diagnostics

• Error - Prevents code generation or compilation
• Warning - Indicates potential issues or non-recommended patterns
• Info - Suggestions for improvement or informational messages

General Diagnostics (TSG1xxx)

ID	Level	Category	Description
TSG1000	Error	Usage	Fatal execution error occurred during generation.
TSG1001	Error	Usage	Inferring generation targets is not supported when using multi-target generation. Each method must have an explicit attribute.
TSG1002	Error	Usage	Multiple attributes from the same target family are not supported. Only one Activity, Logging, or Metrics attribute per method.
TSG1003	Error	Usage	Duplicate method names are not supported. Method names must be unique as they’re used to generate other members.
TSG1004	Error	Usage	Generic interfaces are not supported. Remove generic type parameters from the interface.
TSG1005	Error	Usage	Generic methods are not supported. Remove generic type parameters from methods.
TSG1006	Warning	Usage	[ExcludeTargets] references a target not present on this method.
TSG1007	Warning	Usage	[ExcludeTargets] results in an empty or invalid parameter set for a target.
TSG1008	Warning	Usage	Activity parameter present but no Activity attribute on method. Parameter will be ignored.
TSG1009	Info	Usage	Tag/baggage key appears to be a compound word without separators. Consider using snake_case or dot.notation.

Logging Diagnostics (TSG2xxx)

ID	Level	Category	Description	Applies To
TSG2000	Error	Usage	Too many exception parameters. Only a single Exception parameter is permitted.	v1, v2
TSG2001	Error	Usage	More than 6 parameters (excluding Exception). Maximum is 6 non-exception parameters.	v1, v2
TSG2002	Info	Usage	Inferring Error log level because an Exception parameter was defined without explicit level.	v1, v2
TSG2003	Warning	Usage	Microsoft.Extensions.Logging.ILogger type not found. Add reference to Microsoft.Extensions.Logging package.	v1, v2
TSG2004	Error	Usage	Cannot mix ordinal and named property placeholders in message template.	v1, v2
TSG2005	Error	Usage	Ordinal values in message template exceed the number of provided parameters.	v1, v2
TSG2006	Error	Usage	Using [LogProperties] and [ExpandEnumerable] on the same parameter is not supported.	v2 only
TSG2007	Warning	Usage	Scoped log methods should not have a LogLevel set. It will be ignored.	v1, v2
TSG2008	Warning	Performance	Unbounded enumeration limit is higher than recommended default (500). May cause performance issues.	v2 only
TSG2020	Error	Usage	Scoped logging methods must return IDisposable? to properly manage log scope lifetime.	v1, v2
TSG2021	Error	Usage	Log methods must return void (non-scoped) or IDisposable? (scoped). Other return types are not supported.	v1, v2
TSG2022	Error	Usage	Async return types (Task, ValueTask) are not supported for logging methods.	v1, v2
TSG2023	Info	Usage	Using Default prefix type results in log names with no context prefix. Consider using TrimmedClassName or Custom.	v1, v2
TSG2024	Warning	Usage	Log method name is very short or generic. Use a more descriptive name.	v1, v2

Activities Diagnostics (TSG3xxx)

ID	Level	Category	Description
TSG3000	Warning	Usage	Baggage parameter types only accept strings. ToString() will be called on non-string types.
TSG3001	Warning	Usage	No activity source name specified. Defaulting to ‘purview’.
TSG3002	Error	Usage	Invalid return type. Activity or Event methods must return void, Activity, or Activity?.
TSG3003	Error	Usage	Duplicate reserved parameters defined. Only one of each reserved parameter type is allowed.
TSG3004	Error	Usage	Activity parameter is not valid on Activity methods, only on Event and Context methods.
TSG3005	Error	Usage	Timestamp parameter is not valid on Activity methods, only on Event methods.
TSG3006	Error	Usage	Start time parameter is only valid when starting an activity, not on Create or Event methods.
TSG3007	Error	Usage	Parent context or Parent Id parameter is only valid on Activity start/create methods, not Events.
TSG3008	Error	Usage	Activity links parameters are only valid on Activity start/create methods, not Events or Context.
TSG3009	Error	Usage	Activity tags parameter is only valid on Activity start/create and Event methods, not Context.
TSG3010	Error	Usage	Escaped parameters must be of type boolean.
TSG3011	Error	Usage	Escaped parameters are only valid on Event methods, not Activity or Context methods.
TSG3012	Info	Usage	No Activity methods defined. Event/Context methods will use Activity.Current which may not be intended.
TSG3013	Warning	Usage	Activity method should return Activity? so it can be disposed and used for Events/Context.
TSG3014	Warning	Usage	Event/Context method should accept an Activity? parameter to ensure it applies to the intended Activity.
TSG3015	Info	Usage	For readability, the Activity parameter should be the first parameter.
TSG3016	Error	Usage	Status description parameter must be of type string.
TSG3017	Error	Usage	Status description parameters are only valid on Event methods, not Activity or Context.
TSG3018	Info	Usage	Span name is generic or reserved (e.g., “process”, “execute”, “run”). Use a more descriptive name.
TSG3019	Info	Usage	ActivitySource name is defaulting to assembly name. Consider specifying explicitly with [ActivitySource(Name = "...")].
TSG3020	Warning	Usage	ActivitySource name cannot be empty or whitespace. Provide a valid name.
TSG3021	Info	Usage	Event records an exception but doesn’t use OpenTelemetry standard name “exception”. Consider [Event(Name = "exception")].

Metrics Diagnostics (TSG4xxx)

ID	Level	Category	Description
TSG4000	Error	Usage	No instrument defined. Add a meter attribute or exclude the method.
TSG4001	Error	Usage	Instrument methods must return void or bool (for observables to indicate initialization).
TSG4002	Error	Usage	Auto increment counter and measurement parameter both defined. Use one or the other.
TSG4003	Error	Usage	Multiple measurement parameters defined. Only one [InstrumentMeasurement] is allowed.
TSG4004	Error	Usage	No measurement value defined. Add [InstrumentMeasurement] parameter or a supported numeric type.
TSG4005	Error	Usage	Observable instruments require a Func<T> parameter where T is a supported measurement result type.
TSG4006	Error	Usage	Invalid measurement type. Valid types: byte, short, int, long, float, double, decimal, Measurement<T>, IEnumerable<Measurement<T>>.
TSG4007	Error	Usage	Observable metrics can only return void or Activity? (when combined with [Activity]). Boolean returns not supported.
TSG4008	Error	Usage	AutoCounter methods must return void. Boolean or other return types are not supported.
TSG4009	Warning	Usage	Instrument name matches the instrument type name (e.g., “counter”, “histogram”). Name what you’re measuring, not the type.
TSG4010	Warning	Usage	Instrument name contains compound words without separators. Consider using dot.notation or snake_case.
TSG4011	Info	Usage	Meter name is defaulting to interface name. Consider using assembly name or explicit name with [Meter(Name = "...")].
TSG4012	Info	Usage	Instrument name starts with instrument type verb (e.g., “RecordDuration”). Name after the concept instead (e.g., “request.duration”).

Common Resolutions

TSG1001 - Multi-target Inference Not Supported

Problem: Using multiple generation targets without explicit method attributes.

Solution:

// Bad - inference not supported with multi-target
[ActivitySource("MyApp")]
[Logger]
[Meter]
interface IMyTelemetry
{
    void DoSomething(int id);  // ERROR: No explicit attribute
}

// Good - explicit attributes
[ActivitySource("MyApp")]
[Logger]
[Meter]
interface IMyTelemetry
{
    [Activity]
    [Info]
    [AutoCounter]
    Activity? DoSomething(int id);
}

TSG1003 - Duplicate Method Names

Problem: Multiple methods with the same name.

Solution:

// Bad
interface IMyTelemetry
{
    [Info]
    void ProcessItem(int id);

    [Info]
    void ProcessItem(string name);  // ERROR: Duplicate name
}

// Good - unique names
interface IMyTelemetry
{
    [Info]
    void ProcessItemById(int id);

    [Info]
    void ProcessItemByName(string name);
}

TSG2020 - Scoped Log Must Return IDisposable

Problem: Scoped log doesn’t return IDisposable?.

Solution:

// Bad
[Logger]
interface IMyTelemetry
{
    [Log]
    void ProcessingScope(int id);  // ERROR: Should return IDisposable?
}

// Good
[Logger]
interface IMyTelemetry
{
    [Log]
    IDisposable? ProcessingScope(int id);  // Scoped log
}

TSG3013/TSG3014 - Activity Best Practices

Problem: Activity not returned or Event doesn’t accept Activity parameter.

Solution:

// Bad
[ActivitySource("MyApp")]
interface IMyTelemetry
{
    [Activity]
    void ProcessItem(int id);  // Warning: Should return Activity?

    [Event]
    void ItemProcessed(int id);  // Warning: Should accept Activity?
}

// Good
[ActivitySource("MyApp")]
interface IMyTelemetry
{
    [Activity]
    Activity? ProcessItem(int id);

    [Event]
    void ItemProcessed(Activity? activity, int id);
}

TSG4002 - AutoCounter vs Measurement

Problem: AutoCounter with measurement parameter.

Solution:

// Bad
[Meter]
interface IMyMetrics
{
    [AutoCounter]
    void Count([InstrumentMeasurement]int value);  // ERROR: AutoCounter doesn't need measurement
}

// Good - Option 1: Use AutoCounter (always increments by 1)
[Meter]
interface IMyMetrics
{
    [AutoCounter]
    void Count([Tag]string type);
}

// Good - Option 2: Use Counter with measurement
[Meter]
interface IMyMetrics
{
    [Counter]
    void Count([InstrumentMeasurement]int value, [Tag]string type);
}

See Also

• Getting Started - Quick start examples
• Activities - Activity generation details
• Logging - Logging generation details
• Metrics - Metrics generation details