DiagFailedToConvertCty is an error that can happen late in parsing.

DiagFileNotFound is returned when pack parsing encounters a required file that is missing.

DiagInvalidDefaultValue is returned when the default for a variable does not match the specified variable type.

DiagInvalidValueForType is returned when a pack consumer attempts to set a variable to an inappopriate value based on the pack's variable specification.

DiagInvalidVariableName is returned when a pack author specifies an invalid name for a variable in their varfile.

DiagMissingRootVar is returned when a pack consumer passes in a variable that is not defined for the pack.

SafeDiagnosticsAppend prevents a nil Diagnostic from appending to the target Diagnostics, since HasError is not nil-safe.

SafeDiagnosticsExtend clean where the input Diagnostics of nils as they are appended to the base.