F_SYSTEM_* errors identify invalid command definitions or application registration. They are developer-facing failures: func stops immediately instead of sending them through command-local or global error handlers.
When funcgo recognizes one of these errors during development or a build check, it keeps the original error output and adds a link to the matching page below. Use the code to find the relevant invariant, minimal reproduction, and fix.
2.x Current
System errors emitted by current func versions
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F_SYSTEM_CANNOT_INFER_VALUE_TYPECannot infer value type
A @Value property has no supported runtime type and does not declare one explicitly.
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F_SYSTEM_DUPLICATE_COMMAND_TOKENDuplicate command token
Two registered commands use the same name or alias.
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F_SYSTEM_DUPLICATE_OPTION_TOKENDuplicate option token
Multiple fields, sub-options, handler flags, or handler paths claim the same token in one command.
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F_SYSTEM_EXPECTED_ARRAY_PARAMExpected an array parameter
A decorator parameter such as path, SubOptions, Enum, DependsOn, or Exclusive is not an array.
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F_SYSTEM_HANDLER_ALIAS_REQUIRES_FLAGHandler alias requires a flag
A @Handler declares an alias without declaring the flag that alias should abbreviate.
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F_SYSTEM_HANDLER_FLAG_PATH_CONFLICTHandler flag conflicts with path
A @Handler tries to select the same method by both an option flag and a positional path.
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F_SYSTEM_HANDLER_PATH_ALIAS_CONFLICTHandler path does not support alias
A path-selected @Handler also declares an alias, which is only valid for handler flags.
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F_SYSTEM_INVALID_FIELD_DECORATOR_TARGETInvalid field decorator target
A field option or validator decorator is attached to something other than an instance property.
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F_SYSTEM_INVALID_METHOD_DECORATOR_TARGETInvalid method decorator target
@Handler or @Catch is attached to something other than an instance method.
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F_SYSTEM_INVALID_OPTION_ALIASInvalid option alias
A command, field option, sub-option, or handler flag uses an alias longer than one character.
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F_SYSTEM_INVALID_TOKENInvalid command or option token
A command, option, alias, flag, or path token is empty, starts with a hyphen, or contains whitespace.
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F_SYSTEM_MISSING_HANDLERMissing command handler
A command does not define any @Handler method.
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F_SYSTEM_MISSING_REQUIRED_PARAMMissing required decorator parameter
A command or option declaration omits a required name or another standalone value.
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F_SYSTEM_MULTIPLE_DEFAULT_HANDLERSMultiple default handlers
One command declares more than one @Handler without a flag or path.
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F_SYSTEM_MULTIPLE_MAJOR_COMMANDSMultiple major commands
The application registers more than one command as its root command.
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F_SYSTEM_MULTIPLE_MISSING_COMMANDSMultiple missing commands
The application registers more than one fallback for unknown command names.
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F_SYSTEM_NO_MATCHING_HANDLERNo matching handler
A command has handlers, but the current invocation matches no path or flag and no default handler exists.
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F_SYSTEM_UNKNOWN_HANDLERUnknown registered handler
A class registered with the application does not carry any func command or error-handler metadata.
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F_SYSTEM_UNSUPPORTED_ARRAY_TYPEUnsupported Array option type
An option uses the generic Array constructor instead of the supported repeated-string parser.
1.x
Codes retained for older versions and existing links
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F_SYSTEM_DUPLICATE_HANDLERDuplicate handler registration
Two command definitions claim a handler role or token that must be unique within the same application scope.
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F_SYSTEM_INVALID_PARAM_TYPEInvalid decorator parameter type
A decorator target or parameter does not have the runtime shape required by func.
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F_SYSTEM_INVALID_PARAM_VALUEInvalid decorator parameter value
A decorator parameter has the correct general type but violates a func naming or handler-shape rule.
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F_SYSTEM_MISSING_PARAM_TYPESMissing parameter type metadata
An older func runtime could not inspect constructor parameter types required for injection.
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F_SYSTEM_MISSING_PROVIDERMissing injection provider
An older func runtime could not find a provider for a constructor parameter.