1 files changed, 135 insertions, 0 deletions
diff --git a/src/errors/wrap.go b/src/errors/wrap.go
new file mode 100644
index 0000000..a719655
--- /dev/null
+++ b/src/errors/wrap.go
@@ -0,0 +1,135 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package errors
+
+import (
+	"internal/reflectlite"
+)
+
+// Unwrap returns the result of calling the Unwrap method on err, if err's
+// type contains an Unwrap method returning error.
+// Otherwise, Unwrap returns nil.
+//
+// Unwrap returns nil if the Unwrap method returns []error.
+func Unwrap(err error) error {
+	u, ok := err.(interface {
+		Unwrap() error
+	})
+	if !ok {
+		return nil
+	}
+	return u.Unwrap()
+}
+
+// Is reports whether any error in err's tree matches target.
+//
+// The tree consists of err itself, followed by the errors obtained by repeatedly
+// calling Unwrap. When err wraps multiple errors, Is examines err followed by a
+// depth-first traversal of its children.
+//
+// An error is considered to match a target if it is equal to that target or if
+// it implements a method Is(error) bool such that Is(target) returns true.
+//
+// An error type might provide an Is method so it can be treated as equivalent
+// to an existing error. For example, if MyError defines
+//
+//	func (m MyError) Is(target error) bool { return target == fs.ErrExist }
+//
+// then Is(MyError{}, fs.ErrExist) returns true. See syscall.Errno.Is for
+// an example in the standard library. An Is method should only shallowly
+// compare err and the target and not call Unwrap on either.
+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
+		}
+		switch x := err.(type) {
+		case interface{ Unwrap() error }:
+			err = x.Unwrap()
+			if err == nil {
+				return false
+			}
+		case interface{ Unwrap() []error }:
+			for _, err := range x.Unwrap() {
+				if Is(err, target) {
+					return true
+				}
+			}
+			return false
+		default:
+			return false
+		}
+	}
+}
+
+// As finds the first error in err's tree that matches target, and if one is found, sets
+// target to that error value and returns true. Otherwise, it returns false.
+//
+// The tree consists of err itself, followed by the errors obtained by repeatedly
+// calling Unwrap. When err wraps multiple errors, As examines err followed by a
+// depth-first traversal of its children.
+//
+// An error matches target if the error's concrete value is assignable to the value
+// pointed to by target, or if the error has a method As(interface{}) bool such that
+// As(target) returns true. In the latter case, the As method is responsible for
+// setting target.
+//
+// An error type might provide an As method so it can be treated as if it were a
+// different error type.
+//
+// As panics if target is not a non-nil pointer to either a type that implements
+// error, or to any interface type.
+func As(err error, target any) bool {
+	if err == nil {
+		return false
+	}
+	if target == nil {
+		panic("errors: target cannot be nil")
+	}
+	val := reflectlite.ValueOf(target)
+	typ := val.Type()
+	if typ.Kind() != reflectlite.Ptr || val.IsNil() {
+		panic("errors: target must be a non-nil pointer")
+	}
+	targetType := typ.Elem()
+	if targetType.Kind() != reflectlite.Interface && !targetType.Implements(errorType) {
+		panic("errors: *target must be interface or implement error")
+	}
+	for {
+		if reflectlite.TypeOf(err).AssignableTo(targetType) {
+			val.Elem().Set(reflectlite.ValueOf(err))
+			return true
+		}
+		if x, ok := err.(interface{ As(any) bool }); ok && x.As(target) {
+			return true
+		}
+		switch x := err.(type) {
+		case interface{ Unwrap() error }:
+			err = x.Unwrap()
+			if err == nil {
+				return false
+			}
+		case interface{ Unwrap() []error }:
+			for _, err := range x.Unwrap() {
+				if As(err, target) {
+					return true
+				}
+			}
+			return false
+		default:
+			return false
+		}
+	}
+}
+
+var errorType = reflectlite.TypeOf((*error)(nil)).Elem()