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.
F_SCAFFOLD_* errors identify failures in funcgo, create-func, and related ecosystem tooling. Their pages explain which project or environment input to correct before retrying the command.
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.
Framework errors
Errors emitted by the func framework itself
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F_SYSTEM_AMBIGUOUS_OPTION_SCOPEAmbiguous option scope
A shared Command path belongs to multiple features with Module options, so no single rule set can be selected.
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F_SYSTEM_CANNOT_INFER_VALUE_TYPECannot infer value type
A value property does not expose supported TypeScript decorator metadata.
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F_SYSTEM_CIRCULAR_MODULE_IMPORTCircular Module import
A dependency path in Module.imports leads back to a Module that is already being compiled.
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F_SYSTEM_CIRCULAR_PROVIDER_DEPENDENCYCircular Provider dependency
The same token reappeared in an unfinished dependency path while resolving a Provider.
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F_SYSTEM_DUPLICATE_APPLICATION_FEATUREDuplicate application feature
createApp received more than one application feature with the same key.
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F_SYSTEM_DUPLICATE_COMMAND_TOKENDuplicate command token
Two registered commands use the same path token or alias under one parent path.
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F_SYSTEM_DUPLICATE_OPTION_TOKENDuplicate option token
A field, Module option, or action option claims the same token at one command node.
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F_SYSTEM_DUPLICATE_PROVIDERDuplicate or ambiguous Provider token
A Module registered the same token more than once, or a consumer can see multiple imported Providers for it.
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F_SYSTEM_EXPECTED_ARRAY_PARAMExpected an array parameter
A list parameter such as aliases, 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 alias or aliases without declaring the flag they 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_INTERNAL_INVARIANTInconsistent internal runtime state
The Func compiler or argument parser reached a state that the public API contract should make impossible.
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F_SYSTEM_INVALID_APP_NAMEInvalid application name
An appName passed to Config, Log, or another disk-backed feature is not a safe single path segment.
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F_SYSTEM_INVALID_APPLICATION_FEATUREInvalid application feature
A value in createApp.features was not created by a Func feature factory.
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F_SYSTEM_INVALID_APPLICATION_FEATURE_LISTInvalid application feature list
createApp.features is not an array of ApplicationFeature objects.
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F_SYSTEM_INVALID_ARGS_DECORATOR_TARGETInvalid @Args target
@Args was placed on a constructor parameter rather than a Command Handler parameter.
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F_SYSTEM_INVALID_COMPLETION_BINInvalid completion executable name
The bin passed to func/completion is empty, contains whitespace, or contains a NUL character.
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F_SYSTEM_INVALID_COMPLETION_MODEInvalid completion mode
The completion environment variable contains a source or complete mode unsupported by func/completion.
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F_SYSTEM_INVALID_COMPLETION_REQUESTInvalid completion request
complete() received args that are not a string array, or an incomplete value that is not a string.
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F_SYSTEM_INVALID_COMPLETION_SHELLInvalid completion shell
completionSource() received an unsupported shell name.
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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
A method decorator is attached to an unsupported target or handler kind.
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F_SYSTEM_INVALID_MODULE_EXPORTInvalid Module export
Module.exports contains a Provider token that is unregistered, unimported, or invisible to the Module.
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F_SYSTEM_INVALID_MODULE_INPUTInvalid module input
A class passed as a module does not carry explicit module metadata.
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F_SYSTEM_INVALID_OPTION_ALIASInvalid option alias
A field option, option command, or handler flag contains an alias that is not exactly one character.
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F_SYSTEM_INVALID_OPTION_DECLARATIONInvalid Module option declaration
A value in Module.options is not a valid @Option or @OptionCommand class.
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F_SYSTEM_INVALID_OPTION_TYPEInvalid option type
A field decorator does not match the property's emitted runtime type.
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F_SYSTEM_INVALID_OVERRIDE_TARGETInvalid option override target
@Override does not decorate exactly one instance field option, or it is used on an unsupported target.
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F_SYSTEM_INVALID_PROVIDERInvalid Provider definition
A class or explicit Provider object in Module.providers does not satisfy the DI registration rules.
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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_APP_NAMEMissing application name
Config, Log, or another feature that requires an application directory did not receive appName.
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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_PARAM_TYPESMissing parameter type metadata
The runtime cannot infer the Provider token requested by a constructor or Handler parameter.
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F_SYSTEM_MISSING_PROVIDERMissing injection Provider
The current Module cannot see a Provider token requested by a constructor, Handler, or factory.
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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_OPTION_OVERRIDE_REQUIREDExplicit option override required
An inner scope declares a field or action with the same name as an outer Module option without confirming the override.
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F_SYSTEM_UNKNOWN_HANDLERUnknown registered Handler
A registered Command lacks role metadata, or a Provider declares an @Handler method.
Scaffolding errors
Scaffolding errors emitted by funcgo and create-func
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F_SCAFFOLD_COMMAND_FAILEDChild command failed
funcgo could not start a child command or the command exited unsuccessfully.
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F_SCAFFOLD_ENTRY_NOT_FOUNDProject entry not found
funcgo could not resolve the TypeScript entry to run or build.
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F_SCAFFOLD_INTERNAL_COMMAND_MISMATCHInternal tooling command mismatch
The command parsed by the scaffolding runtime does not match the action currently being executed.
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F_SCAFFOLD_INVALID_PACKAGE_METADATAInvalid package metadata
Package metadata read from package.json does not have the expected shape.
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F_SCAFFOLD_INVALID_PROJECT_NAMEInvalid project name
create-func received a project name that is unsafe as either a package name or directory name.
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F_SCAFFOLD_MULTIPLE_PROJECT_NAMESMultiple project names
create-func received more than one positional project name.
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F_SCAFFOLD_NEGATIVE_WATCH_GLOBNegative watch glob is unsupported
A funcgo watch entry uses an exclusion glob beginning with !.
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F_SCAFFOLD_PACKAGE_MANIFEST_NOT_FOUNDPackage manifest not found
funcgo could not find package.json in the target project.
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F_SCAFFOLD_PROJECT_EXISTSProject directory already exists
create-func will not overwrite an existing target path.
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F_SCAFFOLD_TEMPLATE_DOWNLOAD_FAILEDTemplate download failed
create-func could not download project files from the template source.
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F_SCAFFOLD_TEMPLATE_METADATA_INVALIDInvalid template metadata
The downloaded template manifest cannot be parsed or is missing required information.
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F_SCAFFOLD_WATCH_GLOB_BASE_NOT_FOUNDWatch glob base not found
funcgo cannot find the directory before the first wildcard in a watch glob.
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F_SCAFFOLD_WATCH_PATH_NOT_FOUNDWatch path not found
A watch file or directory passed to funcgo does not exist in the project.
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F_SCAFFOLD_WATCH_REQUIRES_WATCHWatch option requires watch mode
funcgo received an option that is valid only in watch mode, but watch mode is disabled.