Analyzer diagnostics

Mapperly emits several diagnostics:

Rule ID	Severity	Description
RMG001	Error	A mapping method has an unsupported signature.
RMG002	Error	No accessible parameterless constructor found.
RMG003	Warning	No overlapping enum members found.
RMG004	Warning	Ignored target member not found.
RMG005	Error	Mapping target member not found.
RMG006	Error	Mapping source member not found.
RMG007	Error	Could not map member.
RMG008	Error	Could not create mapping.
RMG009	Info	Cannot map to read only member.
RMG010	Info	Cannot map from write only member.
RMG011	Info	Cannot map to write only member path.
RMG012	Warning	Source member was not found for target member
RMG013	Error	No accessible constructor with mappable arguments found
RMG014	Warning	Cannot map to the configured constructor to be used by Mapperly
RMG015	Info	Cannot map to init only member path
RMG016	Error	Init only member cannot handle target paths
RMG020	Warning	Source member is not mapped to any target member
RMG021	Warning	Ignored source member not found
RMG022	Error	Invalid object factory signature
RMG023	Error	Mapping source member for a required target member not found
RMG024	Error	The reference handler parameter is not of the correct type
RMG025	Error	To use reference handling it needs to be enabled on the mapper attribute
RMG029	Error	Queryable projection mappings do not support reference handling
RMG030	Error	Reference loop detected while mapping to an init only member
RMG031	Warning	Reference loop detected while mapping to a constructor member
RMG032	Warning	The enum mapping strategy ByName cannot be used in projection mappings
RMG033	Info	Object mapped to another object without deep clone
RMG034	Error	Derived source type is specified multiple times, a source type may only be specified once
RMG035	Error	Derived source type is not assignable to parameter type
RMG036	Error	Derived target type is not assignable to return type
RMG037	Warning	An enum member could not be found on the source enum
RMG038	Warning	An enum member could not be found on the target enum
RMG039	Error	Enum source value is specified multiple times, a source enum value may only be specified once
RMG040	Error	A target enum member value does not match the target enum type
RMG041	Error	A source enum member value does not match the source enum type
RMG042	Error	The type of the enum fallback value does not match the target enum type
RMG043	Warning	Enum fallback values are only supported for the ByName and ByValueCheckDefined strategies, but not for the ByValue strategy
RMG044	Warning	An ignored enum member can not be found on the source enum
RMG045	Warning	An ignored enum member can not be found on the target enum
RMG046	Error	The used C# language version is not supported by Mapperly, Mapperly requires at least C# 9.0
RMG047	Error	Cannot map to member path due to modifying a temporary value, see CS1612
RMG048	Error	Used mapper members cannot be nullable
RMG049	Warning	Source member is ignored and also explicitly mapped
RMG050	Warning	Target member is ignored and also explicitly mapped
RMG051	Warning	Invalid ignore source member found, nested ignores are not supported
RMG052	Warning	Invalid ignore target member found, nested ignores are not supported
RMG053	Error	The flag MemberVisibility.Accessible cannot be disabled, this feature requires .NET 8.0 or greater
RMG054	Error	Mapper class containing 'static partial' method must not have any instance methods
RMG055	Error	The source type does not implement ToString with the provided formatting parameters, string format and format provider cannot be applied
RMG056	Error	Invalid format provider signature
RMG057	Error	Format provider not found
RMG058	Error	Multiple default format providers found, only one is allowed
RMG059	Error	Multiple default user mappings found, only one is allowed
RMG060	Warning	Multiple user mappings discovered without specifying an explicit default
RMG061	Error	The referenced mapping was not found
RMG062	Error	The referenced mapping name is ambiguous
RMG063	Error	Cannot configure an enum mapping on a non-enum mapping
RMG064	Error	Cannot configure an object mapping on a non-object mapping
RMG065	Warning	Cannot configure an object mapping on a queryable projection mapping, apply the configurations to an object mapping method instead
RMG066	Warning	No members are mapped in an object mapping
RMG067	Error	Invalid usage of the MapPropertyAttribute
RMG068	Info	Cannot inline user implemented queryable expression mapping
RMG069	Warning	Runtime target type or generic type mapping does not match any mappings
RMG070	Error	Mapping nested member not found
RMG071	Warning	Nested properties mapping is not used
RMG072	Warning	The source type of the referenced mapping does not match
RMG073	Warning	The target type of the referenced mapping does not match
RMG074	Error	Multiple mappings are configured for the same target member
RMG075	Error	Invalid usage of the MapValueAttribute
RMG076	Warning	Cannot assign null to non-nullable member
RMG077	Error	Cannot assign constant value because the type of the value does not match the type of the target
RMG078	Error	Cannot assign method return type because the type of the value does not match the type of the target
RMG079	Error	The referenced method could not be found or has an unsupported signature
RMG080	Error	The MapValueAttribute does not support types and arrays
RMG081	Error	A mapping method with additional parameters cannot be a default mapping
RMG082	Warning	An additional mapping method parameter is not mapped
RMG083	Info	Cannot map to read only type
RMG084	Error	Multiple mappings are configured for the same source string
RMG085	Error	Invalid usage of fallback value
RMG086	Error	The source of the explicit mapping from a string to an enum is not of type string
RMG087	Error	The target of the explicit mapping from an enum to a string is not of type string
RMG088	Info	The attribute to build the name of the enum member is missing
RMG089	Info	Mapping nullable source to non-nullable target member
RMG090	Info	Mapping nullable source type to non-nullable target type
RMG091	Error	Circular included mapping configuration detected
RMG092	Error	Source type is not assignable to the included source type
RMG093	Error	Target type is not assignable to the included target type

info

Mapperly only emits updated source code on build. You won't see the updated mapper code or mapper diagnostics until you perform a build.

This is done for performance reasons, otherwise the IDE could become laggy.

Editorconfig

The severity of these diagnostics can be customized via an .editorconfig file:

.editorconfig

[*.cs]
dotnet_diagnostic.{RuleID}.severity = error
dotnet_diagnostic.RMG020.severity = error

See also code analysis configurations and available severity levels.

Suppress diagnostics

See the Microsoft documentation on how to suppress diagnostics in C# here. In summary, you can use one of the following approaches:

• Use the .editorconfig file (for an entire file, directory or project, depending on the editorconfig scope)
  dotnet_diagnostic.RMG066.severity = none
• Use the SuppressMessageAttribute (for a method)
  [SuppressMessage("Mapper", "RMG066:No members are mapped in an object mapping")]
• Use precompiler directives (for specific lines of code)
  #pragma warning disable RMG066 // No members are mapped in an object mapping
#pragma warning restore RMG066 // No members are mapped in an object mapping