rlp: fix staticcheck warnings (#20368)

* rlp: fix staticcheck warnings

* rlp: fix ExampleDecode test

rlp/decode.go

@@ -29,12 +29,13 @@ import (
 	"sync"
 )
 
-var (
+//lint:ignore ST1012 EOL is not an error.
+
 // EOL is returned when the end of the current list
 // has been reached during streaming.
-	EOL = errors.New("rlp: end of list")
+var EOL = errors.New("rlp: end of list")
 
-	// Actual Errors
+var (
 	ErrExpectedString   = errors.New("rlp: expected String or Byte")
 	ErrExpectedList     = errors.New("rlp: expected List")
 	ErrCanonInt         = errors.New("rlp: non-canonical integer format")

rlp/decode_test.go

@@ -354,7 +354,7 @@ type tailUint struct {
 type tailPrivateFields struct {
 	A    uint
 	Tail []uint `rlp:"tail"`
-	x, y bool
+	x, y bool   //lint:ignore U1000 unused fields required for testing purposes.
 }
 
 type nilListUint struct {
@@ -807,7 +807,6 @@ func ExampleDecode() {
 
 	type example struct {
 		A, B   uint
-		private uint // private fields are ignored
 		String string
 	}
 
@@ -819,7 +818,7 @@ func ExampleDecode() {
 		fmt.Printf("Decoded value: %#v\n", s)
 	}
 	// Output:
-	// Decoded value: rlp.example{A:0xa, B:0x14, private:0x0, String:"foobar"}
+	// Decoded value: rlp.example{A:0xa, B:0x14, String:"foobar"}
 }
 
 func ExampleDecode_structTagNil() {