Package warnings implements error handling with non-fatal errors (warnings).

import path:   "gopkg.in/warnings.v0"
package docs:  https://godoc.org/gopkg.in/warnings.v0
issues:        https://github.com/go-warnings/warnings/issues
pull requests: https://github.com/go-warnings/warnings/pulls

A recurring pattern in Go programming is the following:

 func myfunc(params) error {
     if err := doSomething(...); err != nil {
         return err
     }
     if err := doSomethingElse(...); err != nil {
         return err
     }
     if ok := doAnotherThing(...); !ok {
         return errors.New("my error")
     }
     ...
     return nil
 }

This pattern allows interrupting the flow on any received error. But what if
there are errors that should be noted but still not fatal, for which the flow
should not be interrupted? Implementing such logic at each if statement would
make the code complex and the flow much harder to follow.

Package warnings provides the Collector type and a clean and simple pattern
for achieving such logic. The Collector takes care of deciding when to break
the flow and when to continue, collecting any non-fatal errors (warnings)
along the way. The only requirement is that fatal and non-fatal errors can be
distinguished programmatically; that is a function such as

 IsFatal(error) bool

must be implemented. The following is an example of what the above snippet
could look like using the warnings package:

 import "gopkg.in/warnings.v0"

 func isFatal(err error) bool {
     _, ok := err.(WarningType)
     return !ok
 }

 func myfunc(params) error {
     c := warnings.NewCollector(isFatal)
     c.FatalWithWarnings = true
     if err := c.Collect(doSomething()); err != nil {
         return err
     }
     if err := c.Collect(doSomethingElse(...)); err != nil {
         return err
     }
     if ok := doAnotherThing(...); !ok {
         if err := c.Collect(errors.New("my error")); err != nil {
             return err
         }
     }
     ...
     return c.Done()
 }

For an example of a non-trivial code base using this library, see
gopkg.in/gcfg.v1

Rules for using warnings

 - ensure that warnings are programmatically distinguishable from fatal
   errors (i.e. implement an isFatal function and any necessary error types)
 - ensure that there is a single Collector instance for a call of each
   exported function
 - ensure that all errors (fatal or warning) are fed through Collect
 - ensure that every time an error is returned, it is one returned by a
   Collector (from Collect or Done)
 - ensure that Collect is never called after Done