xerrors: make As match on assignability
Change As to consider assignability rather than type equivalence, allowing
it to convert an error to an interface type. e.g.,
var to interface{ Timeout() bool }
if errors.As(err, &to) && to.Timeout() { ... }j
Change-Id: Ia3ecaefb6c27f878f81f1d467b07b69fee9db976
Reviewed-on: https://go-review.googlesource.com/c/161017
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/wrap.go b/wrap.go
index eee732b..2462d3d 100644
--- a/wrap.go
+++ b/wrap.go
@@ -68,9 +68,10 @@
}
// As finds the first error in err's chain that matches the type to which target
-// points, and if so, sets the target to its value and and returns true. An error
-// matches a type if it is of the same type, or if it has a method As(interface{}) bool
-// such that As(target) returns true. As will panic if target is nil or not a pointer.
+// points, and if so, sets the target to its value and returns true. An error
+// matches a type if it is assignable to the target type, or if it has a method
+// As(interface{}) bool such that As(target) returns true. As will panic if target
+// is nil or not a pointer.
//
// The As method should set the target to its value and return true if err
// matches the type to which target points.
@@ -84,7 +85,7 @@
}
targetType := typ.Elem()
for {
- if reflect.TypeOf(err) == targetType {
+ if reflect.TypeOf(err).AssignableTo(targetType) {
reflect.ValueOf(target).Elem().Set(reflect.ValueOf(err))
return true
}
diff --git a/wrap_test.go b/wrap_test.go
index 677b209..2380190 100644
--- a/wrap_test.go
+++ b/wrap_test.go
@@ -80,6 +80,7 @@
func TestAs(t *testing.T) {
var errT errorT
var errP *os.PathError
+ var timeout interface{ Timeout() bool }
var p *poser
_, errF := os.Open("non-existing")
@@ -120,16 +121,24 @@
&p,
true,
}, {
- &poser{"oo", nil},
- &errF,
+ xerrors.New("err"),
+ &timeout,
false,
+ }, {
+ errF,
+ &timeout,
+ true,
+ }, {
+ xerrors.Errorf("path error: %w", errF),
+ &timeout,
+ true,
}}
- for _, tc := range testCases {
- name := fmt.Sprintf("As(Errorf(..., %v), %v)", tc.err, tc.target)
+ for i, tc := range testCases {
+ name := fmt.Sprintf("%d:As(Errorf(..., %v), %v)", i, tc.err, tc.target)
t.Run(name, func(t *testing.T) {
match := xerrors.As(tc.err, tc.target)
if match != tc.match {
- t.Fatalf("match: got %v; want %v", match, tc.match)
+ t.Fatalf("xerrors.As(%T, %T): got %v; want %v", tc.err, tc.target, match, tc.match)
}
if !match {
return