Merge pull request #119 from dyweb/errors/go1.13

[errors] Align interface with go1.13

- Add `Unwrap` and `As`
- Remove `DirectCause`

Author: at15

.travis.yml

@@ -2,8 +2,7 @@ language: go
 sudo: false
 
 go:
-  - "1.11"
-  - "1.12"
+  - "1.13"
   - tip
 
 env:

errors/README.md

@@ -1,32 +1,24 @@
 # Errors
 
-A error package that allows you to wrap/unwrap, multi error and inspect error
+[![GoDoc](https://godoc.org/github.com/dyweb/gommon/errors?status.svg)](https://godoc.org/github.com/dyweb/gommon/errors)
+
+A replacement for `errors` and `pkg/errors`. Supports error wrapping, inspection and multi errors.
+
+- [Survey](doc/survey)
 
 ## Issues
 
 - [#54](https://github.com/dyweb/gommon/issues/54) init 
+- [#62](https://github.com/dyweb/gommon/issues/62) support fmt.Formatter
 
 ## Implementation
 
 - [doc/design](doc/design) contains some survey and design choices we made
-- `Wrap` checks if this is already a `WrappedErr`, if not, it attach stack
+- `Wrap` checks if this is already a `WrappedErr`, if not, it attaches stack
 - `MultiErr` keep a slice of errors, the thread safe version use mutex and returns copy of slice when `Errors` is called
 
-## Survey
-
-- Wrap error with context (stack, cause etc.)
-  - [pkg/errors](doc/pkg-errors.md)
-    - Wrap() add withStack only if no cause with stack present https://github.com/pkg/errors/pull/122/
-  - [juju/errors](doc/juju-errors.md)
-  - [hashicorp/errwrap](doc/hashicorp-errwrap.md)
-  - [ ] https://godoc.org/github.com/gorilla/securecookie#Error
-- Multi errors
-  - [hashicorp/go-multierror](doc/hashicorp-go-multierror.md)
-  - [uber/multierr](doc/uber-multierr.md)
-    - Wish we could tell if the append happened  https://github.com/uber-go/multierr/issues/21
-  - [ ] https://godoc.org/github.com/gorilla/securecookie#MultiError
-
 ## References and Alternatives
 
 - [golang/xerrors](https://github.com/golang/xerrors) Official error wrapping `fmt.Errorf("oh my %w", err)`
-- [rotisserie/eris](https://github.com/rotisserie/eris)
+- [rotisserie/eris](https://github.com/rotisserie/eris)
+- [go-rewrap-errors](https://github.com/xdg-go/go-rewrap-errors) Conver pkg/errors to standard library wrapping

errors/cause.go

@@ -13,7 +13,7 @@ type causer interface {
 // If you want get direct cause, use DirectCause.
 // If error is nil, it will return nil. If error is not wrapped it will return the error itself.
 // error wrapped using https://github.com/pkg/errors also satisfies this interface and can be unwrapped as well.
-// TODO: might consider rename it to Unwrap since we are deprecating causer interface
+// Deprecated: Use Walk if you need root cause or Unwrap if you need direct cause.
 func Cause(err error) error {
 	if err == nil {
 		return nil
@@ -29,21 +29,4 @@ func Cause(err error) error {
 		}
 	}
 	return err
-}
-
-// DirectCause returns the direct cause of the error (if any).
-// It does NOT follow the cause chain all the way down, just the first one (if any),
-// If you want to get root cause, use Cause
-func DirectCause(err error) error {
-	if err == nil {
-		return nil
-	}
-	switch err.(type) {
-	case Wrapper:
-		return err.(Wrapper).Unwrap()
-	case causer:
-		return err.(causer).Cause()
-	default:
-		return err
-	}
-}
+}

errors/cause_test.go

@@ -21,18 +21,4 @@ func TestCause(t *testing.T) {
 
 	stderr := stderrors.New("std")
 	assert.Equal(t, stderr, errors.Cause(stderr))
-}
-
-func TestDirectCause(t *testing.T) {
-	assert.Nil(t, errors.DirectCause(nil))
-
-	errw := errors.Wrap(os.ErrClosed, "can't open closed file")
-	errww := errors.Wrap(errw, "wrap again")
-	assert.Equal(t, os.ErrClosed, errors.Cause(errww))
-	assert.Equal(t, os.ErrClosed, errors.Cause(errw))
-	assert.NotEqual(t, os.ErrClosed, errors.DirectCause(errww))
-	assert.Equal(t, "can't open closed file", errors.DirectCause(errww).(errors.Messenger).Message())
-
-	stderr := stderrors.New("std")
-	assert.Equal(t, stderr, errors.DirectCause(stderr))
-}
+}

errors/doc/design/2020-01-17-go1.13-errors.md

@@ -0,0 +1,48 @@
+# 2020-01-17 Go1.13 errors
+
+Since go 1.13, the standard `errors` library also ships with error wrapping.
+This is a follow up on the old issue [#109](https://github.com/dyweb/gommon/issues/109)
+
+## Working with Errors in Go 1.13
+
+https://blog.golang.org/go1.13-errors
+
+- error can define custom `Is`, kind of like overloading `==` operator
+- [ ] can also define custom `As`?
+- don't wrap using `%w` if you don't want user to inspect
+- wrap sentinel error instead of returning it directly
+
+## Implementation
+
+Is
+
+- checks if errors are comparable before comparing them
+- allows err to define a `Is` method, it does not allow target to define `Is` though.
+- it didn't define a public interface for `Is` and uses `interface{ Is(error) bool }` instead
+
+```go
+func Is(err, target error) bool {
+	if target == nil {
+		return err == target
+	}
+
+	isComparable := reflectlite.TypeOf(target).Comparable()
+	for {
+		if isComparable && err == target {
+			return true
+		}
+		if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) {
+			return true
+		}
+		// TODO: consider supporing target.Is(err). This would allow
+		// user-definable predicates, but also may allow for coping with sloppy
+		// APIs, thereby making it easier to get away with them.
+		if err = Unwrap(err); err == nil {
+			return false
+		}
+	}
+}
+```
+
+As
+

errors/doc/survey/README.md

@@ -0,0 +1,13 @@
+# Survey of go error handling libraries
+
+- Wrap error with context (stack, cause etc.)
+  - [pkg/errors](pkg-errors.md)
+    - Wrap() add withStack only if no cause with stack present https://github.com/pkg/errors/pull/122/
+  - [juju/errors](juju-errors.md)
+  - [hashicorp/errwrap](hashicorp-errwrap.md)
+  - [ ] https://godoc.org/github.com/gorilla/securecookie#Error
+- Multi errors
+  - [hashicorp/go-multierror](hashicorp-go-multierror.md)
+  - [uber/multierr](uber-multierr.md)
+    - Wish we could tell if the append happened  https://github.com/uber-go/multierr/issues/21
+  - [ ] https://godoc.org/github.com/gorilla/securecookie#MultiError