* Introduce errors.Stacktrace
Introduce a new type to replace the unnamed return value from
`Stacktrace()`. `Stacktrace` implements `fmt.Formatter` and currently
replicates the default behaviour of printing a `[]Frame`.
In a future PR the values of `%+v` and `%#v` will be extended to
implement a more readable stacktrace.
* Use fmt.Formatter throughout
Replace Fprintf with fmt.Formatter logic on various types. This
effectively guts Fprint to be just a recursive call down the err.Cause
chain. The next step will be to move this recursive logic into
wrapper.Format.
This change necessitates adding types for the error impls returned from
New and Errorf, and Wrap and Wrapf, respectively. The name of the latter
type is acceptable, the former is not and alternative suggestions are
encouraged.
- Remove cause.Format
- Added fmt.Formatter tests. The location is temporary, once this PR is merged and Fprint removed
they will be merged into errors_test.go
* Introduce Stacktrace and Frame
This PR is a continuation of a series aimed at exposing the stack trace
information embedded in each error value. The secondary effect is to
deprecated the `Fprintf` helper.
Taking cues from from @chrishines' `stack` package this PR introduces a
new interface `Stacktrace() []Frame` and a `Frame` type, similar in
function to the `runtime.Frame` type (although lacking its iterator
type). Each `Frame` implemnts `fmt.Formatter` allowing it to print
itself.
The older `Location` interface is still supported but also deprecated.
