Consistent Error Naming & Semantics

[robin (zphia)]

How should we name errors? A library from Upspin keeps it very brief. Their list is:

const (
    Other         Kind = iota // Unclassified error. This value is not printed in the error message.
    Invalid                   // Invalid operation for this type of item.
    Permission                // Permission denied.
    IO                        // External I/O error such as network failure.
    Exist                     // Item already exists.
    NotExist                  // Item does not exist.
    IsDir                     // Item is a directory.
    NotDir                    // Item is not a directory.
    NotEmpty                  // Directory not empty.
    Private                   // Information withheld.
    Internal                  // Internal error or inconsistency.
    CannotDecrypt             // No wrapped key for user with read access.
    Transient                 // A transient error.
    BrokenLink                // Link target does not exist.
)

Which has a few rules I've observed.

• No redundancy.
  It's Exists not AlreadyExists.
  It's Permissions not NoPermissions.
  It would be Argument not InvalidArgument.
• High level.
  No parameter specific errors.
• Describes reason for failing.
  The errors are in the context of what failed.
  It's NotEmpty not IsFull.
• No subject in the error.
  It's Invalid not InvalidArgument or InvalidType and so on.

Though I think the Upspin ones lack the granularity that we want, I find these ideas useful. Building off of #7, I think the following renames would make sense:

• Data state
  • AlreadyExists -> Found
  • ConflictingChanges -> Conflict
  • NotFound
• Parameters
  • BadFormat -> Format
  • InvalidArgument -> Invalid
  • MissingArgument -> Missing
  • Unsupported Type -> Unsupported
  • Unintialized
• General system errors
  • IO
  • DataLoad -> Query
  • Network
• Permissions
  • AccessDenied -> Denied
  • Disabled
  • Limited

One potential problem with this is that we would have overlap in definitions of Missing and NotFound.

[robin (zphia)]

To swing waaay to the other end, is there merit in following this thread? Or should we mix the two?

• State
  • ResourceAlreadyExists
  • ResourceConflictingChanges
  • ResourceNotFound
• Arguments
  • ArgumentBadFormat
  • ArgumentInvalid
  • ArgumentMissing
  • ArgumentUnsupportedType
• Dependency
  • DependencyUninitalized
• General (notice the redundancy of the word "failure" here).
  • IOFailure
  • QueryFailure
  • NetworkFailure
• Permissions
  • AccessDenied
  • ActionDisabled
  • ActionLimited