Revert "encoding/json: implement Is on all errors"

This reverts CL 254537.

Reason for revert: Reason for revert: The recommended way to check for a type of error is errors.As. API changes should also start with a proposal.

Change-Id: I07c37428575e99c80b17525833a61831d10963bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/254857
Trust: Damien Neil <dneil@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

4 files changed, 1 insertions, 84 deletions

diff --git a/src/encoding/json/decode.go b/src/encoding/json/decode.go
index 1b006ffb17..86d8a69db7 100644
--- a/src/encoding/json/decode.go
+++ b/src/encoding/json/decode.go
@@ -136,12 +136,6 @@ func (e *UnmarshalTypeError) Error() string {
 	return "json: cannot unmarshal " + e.Value + " into Go value of type " + e.Type.String()
 }
 
-// Is returns true if target is a UnmarshalTypeError.
-func (e *UnmarshalTypeError) Is(target error) bool {
-	_, ok := target.(*UnmarshalTypeError)
-	return ok
-}
-
 // An UnmarshalFieldError describes a JSON object key that
 // led to an unexported (and therefore unwritable) struct field.
 //
@@ -156,24 +150,12 @@ func (e *UnmarshalFieldError) Error() string {
 	return "json: cannot unmarshal object key " + strconv.Quote(e.Key) + " into unexported field " + e.Field.Name + " of type " + e.Type.String()
 }
 
-// Is returns true if target is a UnmarshalFieldError.
-func (e *UnmarshalFieldError) Is(target error) bool {
-	_, ok := target.(*UnmarshalFieldError)
-	return ok
-}
-
 // An InvalidUnmarshalError describes an invalid argument passed to Unmarshal.
 // (The argument to Unmarshal must be a non-nil pointer.)
 type InvalidUnmarshalError struct {
 	Type reflect.Type
 }
 
-// Is returns true if target is a InvalidUnmarshalError.
-func (e *InvalidUnmarshalError) Is(target error) bool {
-	_, ok := target.(*InvalidUnmarshalError)
-	return ok
-}
-
 func (e *InvalidUnmarshalError) Error() string {
 	if e.Type == nil {
 		return "json: Unmarshal(nil)"
diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index b707dcfa99..219e845c7b 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -2572,34 +2572,3 @@ func TestUnmarshalMaxDepth(t *testing.T) {
 		}
 	}
 }
-
-func TestInvalidUnmarshalErrorIs(t *testing.T) {
-	err := fmt.Errorf("apackage: %w: failed to parse struct", &InvalidUnmarshalError{reflect.TypeOf("a")})
-	if !errors.Is(err, &InvalidUnmarshalError{}) {
-		t.Fatalf("%v should be unwrapped to a InvalidUnmarshalError", err)
-	}
-}
-
-func TestUnmarshalFieldErrorIs(t *testing.T) {
-	err := fmt.Errorf("apackage: %w: failed to parse struct", &UnmarshalFieldError{
-		Key:   "foo",
-		Type:  reflect.TypeOf("a"),
-		Field: reflect.StructField{Name: "b"},
-	})
-	if !errors.Is(err, &UnmarshalFieldError{}) {
-		t.Fatalf("%v should be unwrapped to a UnmarshalFieldError", err)
-	}
-}
-
-func TestUnmarshalTypeErrorIs(t *testing.T) {
-	err := fmt.Errorf("apackage: %w: failed to parse struct", &UnmarshalTypeError{
-		Value:  "foo",
-		Type:   reflect.TypeOf("a"),
-		Offset: 1,
-		Struct: "Foo",
-		Field:  "Bar",
-	})
-	if !errors.Is(err, &UnmarshalTypeError{}) {
-		t.Fatalf("%v should be unwrapped to a UnmarshalTypeError", err)
-	}
-}
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index 8e6b342b59..578d551102 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -245,12 +245,6 @@ func (e *UnsupportedValueError) Error() string {
 	return "json: unsupported value: " + e.Str
 }
 
-// Is returns true if target is a UnsupportedValueError.
-func (e *UnsupportedValueError) Is(target error) bool {
-	_, ok := target.(*UnsupportedValueError)
-	return ok
-}
-
 // Before Go 1.2, an InvalidUTF8Error was returned by Marshal when
 // attempting to encode a string value with invalid UTF-8 sequences.
 // As of Go 1.2, Marshal instead coerces the string to valid UTF-8 by
@@ -285,12 +279,6 @@ func (e *MarshalerError) Error() string {
 // Unwrap returns the underlying error.
 func (e *MarshalerError) Unwrap() error { return e.Err }
 
-// Is returns true if target is a MarshalerError.
-func (e *MarshalerError) Is(target error) bool {
-	_, ok := target.(*MarshalerError)
-	return ok
-}
-
 var hex = "0123456789abcdef"
 
 // An encodeState encodes JSON into a bytes.Buffer.
diff --git a/src/encoding/json/encode_test.go b/src/encoding/json/encode_test.go
index 90826a7f47..7290eca06f 100644
--- a/src/encoding/json/encode_test.go
+++ b/src/encoding/json/encode_test.go
@@ -7,7 +7,6 @@ package json
 import (
 	"bytes"
 	"encoding"
-	"errors"
 	"fmt"
 	"log"
 	"math"
@@ -212,7 +211,7 @@ var unsupportedValues = []interface{}{
 func TestUnsupportedValues(t *testing.T) {
 	for _, v := range unsupportedValues {
 		if _, err := Marshal(v); err != nil {
-			if !errors.Is(err, &UnsupportedValueError{}) {
+			if _, ok := err.(*UnsupportedValueError); !ok {
 				t.Errorf("for %v, got %T want UnsupportedValueError", v, err)
 			}
 		} else {
@@ -1156,24 +1155,3 @@ func TestMarshalerError(t *testing.T) {
 		}
 	}
 }
-
-func TestMarshalerErrorIs(t *testing.T) {
-	err := fmt.Errorf("apackage: %w: failed to parse struct", &MarshalerError{
-		reflect.TypeOf("a"),
-		fmt.Errorf("something"),
-		"TestMarshalerErrorIs",
-	})
-	if !errors.Is(err, &MarshalerError{}) {
-		t.Fatalf("%v should be unwrapped to a MarshalerError", err)
-	}
-}
-
-func TestUnsupportedValueErrorIs(t *testing.T) {
-	err := fmt.Errorf("apackage: %w: failed to parse struct", &UnsupportedValueError{
-		Value: reflect.Value{},
-		Str:   "Foo",
-	})
-	if !errors.Is(err, &UnsupportedValueError{}) {
-		t.Fatalf("%v should be unwrapped to a UnsupportedValueError", err)
-	}
-}