accounts/abi: fix setStruct if src is pointer (e.g. big.Int)

[MariusVanDerWijden]

closes #23551

The issue here was that we were trying to setStruct from a struct to a pointer to a struct, so we need to dereference the pointer first

[rjl493456442]

I tried to reproduce the issue. So it's buggy when we try to assign the resolved value into the receiver.

More specifically, we want to assign struct { A *big.Int} into *contract.ContractStructEvent. Since there is only a single returned value, we enter this path https://github.com/ethereum/go-ethereum/blob/master/accounts/abi/argument.go#L132
Because the receiver is a struct, we should get the first field of struct as the nested value receiver.

So I think the buggy part is here

if dst.Kind() == reflect.Struct && src.Kind() != reflect.Struct {
	return set(dst.Field(0), src)
}

We should use the field(0) anyway no matter the type of resolved value.
Should we fix this issue in the above approach?

if dst.Kind() == reflect.Struct {
	return set(dst.Field(0), src)
}

[rjl493456442]

diff --git a/accounts/abi/argument.go b/accounts/abi/argument.go
index e6d524559..261b4d1b8 100644
--- a/accounts/abi/argument.go
+++ b/accounts/abi/argument.go
@@ -137,7 +137,7 @@ func (arguments Arguments) copyAtomic(v interface{}, marshalledValues interface{
 	dst := reflect.ValueOf(v).Elem()
 	src := reflect.ValueOf(marshalledValues)
 
-	if dst.Kind() == reflect.Struct && src.Kind() != reflect.Struct {
+	if dst.Kind() == reflect.Struct {
 		return set(dst.Field(0), src)
 	}
 	return set(dst, src)
diff --git a/accounts/abi/reflect.go b/accounts/abi/reflect.go
index 11248e073..7af0a1b26 100644
--- a/accounts/abi/reflect.go
+++ b/accounts/abi/reflect.go
@@ -159,7 +159,7 @@ func setArray(dst, src reflect.Value) error {
 		dst.Set(array)
 		return nil
 	}
-	return errors.New("Cannot set array, destination not settable")
+	return errors.New("cannot set array, destination not settable")
 }
 
 func setStruct(dst, src reflect.Value) error {
@@ -167,7 +167,7 @@ func setStruct(dst, src reflect.Value) error {
 		srcField := src.Field(i)
 		dstField := dst.Field(i)
 		if !dstField.IsValid() || !srcField.IsValid() {
-			return fmt.Errorf("Could not find src field: %v value: %v in destination", srcField.Type().Name(), srcField)
+			return fmt.Errorf("could not find src field: %v value: %v in destination", srcField.Type().Name(), srcField)
 		}
 		if err := set(dstField, srcField); err != nil {
 			return err
diff --git a/accounts/abi/unpack_test.go b/accounts/abi/unpack_test.go
index b88f77805..76e43b598 100644
--- a/accounts/abi/unpack_test.go
+++ b/accounts/abi/unpack_test.go
@@ -762,20 +762,23 @@ func TestUnpackTuple(t *testing.T) {
 	buff.Write(common.Hex2Bytes("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff")) // ret[b] = -1
 
 	// If the result is single tuple, use struct as return value container directly.
-	v := struct {
+	type v struct {
 		A *big.Int
 		B *big.Int
-	}{new(big.Int), new(big.Int)}
-
-	err = abi.UnpackIntoInterface(&v, "tuple", buff.Bytes())
+	}
+	type r struct {
+		Result v
+	}
+	var ret0 = new(r)
+	err = abi.UnpackIntoInterface(ret0, "tuple", buff.Bytes())
 	if err != nil {
 		t.Error(err)
 	} else {
-		if v.A.Cmp(big.NewInt(1)) != 0 {
-			t.Errorf("unexpected value unpacked: want %x, got %x", 1, v.A)
+		if ret0.Result.A.Cmp(big.NewInt(1)) != 0 {
+			t.Errorf("unexpected value unpacked: want %x, got %x", 1, ret0.Result.A)
 		}
-		if v.B.Cmp(big.NewInt(-1)) != 0 {
-			t.Errorf("unexpected value unpacked: want %x, got %x", -1, v.B)
+		if ret0.Result.B.Cmp(big.NewInt(-1)) != 0 {
+			t.Errorf("unexpected value unpacked: want %x, got %x", -1, ret0.Result.B)
 		}
 	}

[MariusVanDerWijden]

@rjl493456442 If that works, that would be great. I'm not super great with go reflection.
You can just create a pr with your fix and we close this one

[MariusVanDerWijden]

closed in favor of #23573