Errors and warnings associated with source generators and interceptors

The following errors are generated when source generators or interceptors are loaded during a compilation:

• CS9137: The 'interceptors' experimental feature is not enabled. Add <Features>InterceptorsPreview<Features> to your project.
• CS9138: Method cannot be used as an interceptor because it or its containing type has type parameters.
• CS9139: Cannot intercept: compilation does not contain a file with path.
• CS9140: Cannot intercept: compilation does not contain a file with path. Did you mean to use a different path?
• CS9141: The provided line and character number does not refer to an interceptable method name, but rather to a token.
• CS9142: The given file has n lines, which is fewer than the provided line number m.
• CS9143: The given line is c characters long, which is fewer than the provided character number n.
• CS9144: Cannot intercept method M with interceptor V because the signatures do not match.
• CS9145: Cannot intercept: Path is unmapped. Expected mapped path.
• CS9146: An interceptor method must be an ordinary member method.
• CS9147: The provided line and character number does not refer to the start of a token. Did you mean to use line n and character c?
• CS9148: Interceptor must have a this parameter matching parameter.
• CS9149: Interceptor must not have a this parameter because method does not have a this parameter.
• CS9150: Interceptor cannot have a null file path.
• CS9151: Possible method name M cannot be intercepted because it is not being invoked.
• CS9152: Cannot intercept a call in file with this path because multiple files in the compilation have this path.
• CS9153: The indicated call is intercepted multiple times.
• CS9155: Cannot intercept call with M because it is not accessible within V.
• CS9156: Cannot intercept call to M with V because of a difference in 'scoped' modifiers or [UnscopedRef] attributes.
• CS9157: Line and character numbers provided to InterceptsLocationAttribute must be positive.
• CS9160: A nameof operator cannot be intercepted.
• CS9161: An interceptor cannot be marked with UnmanagedCallersOnlyAttribute.
• CS9177: Interceptor must be non-generic or have matching arity.
• CS9178: Method must be non-generic to match
• CS9206: An interceptor cannot be declared in the global namespace.
• CS9207: Cannot intercept because method is not an invocation of an ordinary member method.
• CS9231: The data argument to InterceptsLocationAttribute is not in the correct format.
• CS9232: Version 'version' of the interceptors format is not supported. The latest supported version is '1'.
• CS9233: Cannot intercept a call in file 'file' because it is duplicated elsewhere in the compilation.
• CS9234: Cannot intercept a call in file 'file' because a matching file was not found in the compilation.
• CS9235: The data argument to InterceptsLocationAttribute refers to an invalid position in file 'file'.

The following warnings are generated when source generators or interceptors are loaded during a compilation:

• CS8784: Generator 'YourSourceGeneratorName' failed to initialize. It will not contribute to the output and compilation errors may occur as a result.
• CS8785: Generator 'YourSourceGeneratorName' failed to generate source. It will not contribute to the output and compilation errors may occur as a result.
• CS9154: Intercepting a call to M with interceptor V, but the signatures do not match.
• CS9158: Nullability of reference types in return type doesn't match interceptable method.
• CS9159: Nullability of reference types in type of parameter doesn't match interceptable method.
• CS9270: 'InterceptsLocationAttribute(string, int, int)' is not supported. Move to 'InterceptableLocation'-based generation of these attributes instead. (https://github.com/dotnet/roslyn/issues/72133)

These errors and warnings follow these themes:

Interceptors are experimental

This error indicates you must enable the experimental feature.

• CS9137: The 'interceptors' experimental feature is not enabled. Add <Features>InterceptorsPreview<Features> to your project.

In C# 12, interceptors are experimental. Interceptors are subject to breaking changes or removal in a future release. Therefore, it is not recommended for production or released applications.

In order to use interceptors, you must set the <Features>InterceptorsPreview<Features> element in your project file. Without this flag, interceptors are disabled, even when other C# 12 features are enabled.

Signature mismatch

The following errors indicate a mismatch between the interceptor method and the interceptable method, or a violation of the rules regarding interceptor method declarations:

• CS9144: Cannot intercept method M with interceptor V because the signatures do not match.
• CS9148: Interceptor must have a this parameter matching parameter.
• CS9149: Interceptor must not have a this parameter because method does not have a this parameter.
• CS9155: Cannot intercept call with M because it is not accessible within V.
• CS9156: Cannot intercept call to M with V because of a difference in 'scoped' modifiers or [UnscopedRef] attributes.
• CS9177]: Interceptor must be non-generic or have matching arity.
• CS9178: Method must be non-generic to match

In addition, the following warnings indicate a mismatch in the signatures of the interceptor and the interceptable method:

• CS9154: Intercepting a call to M with interceptor V, but the signatures do not match.
• CS9158: Nullability of reference types in return type doesn't match interceptable method.
• CS9159: Nullability of reference types in type of parameter doesn't match interceptable method.
• CS9270: 'InterceptsLocationAttribute(string, int, int)' is not supported. Move to 'InterceptableLocation'-based generation of these attributes instead. (https://github.com/dotnet/roslyn/issues/72133)

The interceptor method must be compatible with the interceptable method. You must follow these rules:

• Instance methods can intercept instance methods, not static methods. Similarly, static methods can only intercept static methods, not instance methods.
• The method signatures for the interceptor and the interceptable method must match: They must have the same parameters with the same modifiers in the same order. The return types must also match.
• The ref safe contexts must match. In other words, corresponding ref parameters must be either scoped or not scoped.
• They methods must both be non-generic, or both must have the same number of type parameters.
• An updated InterceptorLocationAttribute constructor signature is preferred.

Incorrect mapping

Interceptors require a source mapping that maps the interceptable method and the interceptor method. The following errors indicate an issue with the mapping:

• CS9139: Cannot intercept: compilation does not contain a file with path.
• CS9140: Cannot intercept: compilation does not contain a file with path. Did you mean to use a different path?
• CS9141: The provided line and character number does not refer to an interceptable method name, but rather to a token.
• CS9142: The given file has n lines, which is fewer than the provided line number m.
• CS9143: The given line is c characters long, which is fewer than the provided character number n.
• CS9145: Cannot intercept: Path is unmapped. Expected mapped path.
• CS9147: The provided line and character number does not refer to the start of a token. Did you mean to use line n and character c?
• CS9150: Interceptor cannot have a null file path.
• CS9157: Line and character numbers provided to InterceptsLocationAttribute must be positive.

Incorrect interceptor declaration

The following errors indicate issues with interceptor declarations, including problems with the InterceptsLocationAttribute format or violations of interceptor rules:

• CS9231: The data argument to InterceptsLocationAttribute is not in the correct format.
• CS9232: Version 'version' of the interceptors format is not supported. The latest supported version is '1'.
• CS9233: Cannot intercept a call in file 'file' because it is duplicated elsewhere in the compilation.
• CS9234: Cannot intercept a call in file 'file' because a matching file was not found in the compilation.
• CS9235: The data argument to InterceptsLocationAttribute refers to an invalid position in file 'file'.
• CS9138: Method cannot be used as an interceptor because it or its containing type has type parameters.
• CS9146: An interceptor method must be an ordinary member method.
• CS9151: Possible method name M cannot be intercepted because it is not being invoked.
• CS9152: Cannot intercept a call in file with this path because multiple files in the compilation have this path.
• CS9153: The indicated call is intercepted multiple times.
• CS9160: A nameof operator cannot be intercepted.
• CS9161: An interceptor cannot be marked with UnmanagedCallersOnlyAttribute.
• CS9206: An interceptor cannot be declared in the global namespace.
• CS9207: Cannot intercept because method is not an invocation of an ordinary member method.

These errors occur when interceptor declarations violate the rules for interceptors or when the InterceptsLocationAttribute contains invalid data:

• CS9231 is generated when the data format doesn't match the expected structure. The attribute requires specifically formatted data that encodes the file path and position information.
• CS9232 indicates you're using a version number that isn't supported. The interceptors feature uses version '1' format. Update your source generator to use the supported version.
• CS9233 happens when the compilation contains multiple files with the same path, making it ambiguous which file to intercept in. Ensure each file in your compilation has a unique path.
• CS9234 is emitted when the file path specified in the attribute doesn't match any file in the current compilation. Verify the file path is correct and the file is included in the compilation.
• CS9235 occurs when the position data (line and character numbers) points to an invalid location in the specified file. This can happen if the position is outside the file's bounds or doesn't correspond to a valid interception point.
• CS9138 prevents generic methods or members of generic classes from being interceptors.
• CS9146 requires interceptors to be ordinary members (not operators, constructors, or finalizers).
• CS9151 prevents intercepting methods that are never invoked.
• CS9152 detects duplicate file paths in the compilation.
• CS9153 prevents multiple interceptions of the same call.
• CS9160 prevents intercepting nameof operators.
• CS9161 prevents interceptors from being marked with UnmanagedCallersOnlyAttribute.
• CS9206 requires interceptors to be contained in a namespace (not global).
• CS9207 requires interceptable methods to be ordinary member invocations.