BUG: Empty encode result in case of zero first byte in child struct as pointer with omitempty tag

[JekaNS]

Encoder return empty json object "{}" In case of encoding struct that has a child as pointer with omitempty tag and this child has first field with value of zero byte (false or 0 or empty string)

Here is the test cases to reproduce:

package jsontest

import (
	"testing"

	"github.com/goccy/go-json"
	"github.com/stretchr/testify/assert"
)

type RootInt struct {
	Child *ChildInt `json:"c,omitempty"`
}

type ChildInt struct {
	Value int `json:"v"`
}

type RootBool struct {
	Child *ChildBool `json:"c,omitempty"`
}

type ChildBool struct {
	Value bool `json:"v"`
}

type RootString struct {
	Child *ChildString `json:"c,omitempty"`
}

type ChildString struct {
	Value string `json:"v"`
}

func TestZeroFirstByteAfterPtrInt(t *testing.T) {
	obj := RootInt{Child: &ChildInt{Value: 0}}

	jsonDst, e2 := json.Marshal(obj)

	assert.NoError(t, e2)
	assert.Equal(t, `{"c":{"v":0}}`, string(jsonDst))
}

func TestNonZeroFirstByteAfterPtrInt(t *testing.T) {
	obj := RootInt{Child: &ChildInt{Value: 1}}

	jsonDst, e2 := json.Marshal(obj)

	assert.NoError(t, e2)
	assert.Equal(t, `{"c":{"v":1}}`, string(jsonDst))
}

func TestZeroFirstByteAfterPtrBool(t *testing.T) {
	obj := RootBool{Child: &ChildBool{Value: false}}

	jsonDst, e2 := json.Marshal(obj)

	assert.NoError(t, e2)
	assert.Equal(t, `{"c":{"v":false}}`, string(jsonDst))
}

func TestNonZeroFirstByteAfterPtrBool(t *testing.T) {
	obj := RootBool{Child: &ChildBool{Value: true}}

	jsonDst, e2 := json.Marshal(obj)

	assert.NoError(t, e2)
	assert.Equal(t, `{"c":{"v":true}}`, string(jsonDst))
}

func TestZeroFirstByteAfterPtrString(t *testing.T) {
	obj := RootString{Child: &ChildString{Value: ""}}

	jsonDst, e2 := json.Marshal(obj)

	assert.NoError(t, e2)
	assert.Equal(t, `{"c":{"v":""}}`, string(jsonDst))
}

func TestNonZeroFirstByteAfterPtrString(t *testing.T) {
	obj := RootString{Child: &ChildString{Value: "a"}}

	jsonDst, e2 := json.Marshal(obj)

	assert.NoError(t, e2)
	assert.Equal(t, `{"c":{"v":"a"}}`, string(jsonDst))
}

Tests run result:

=== RUN   TestZeroFirstByteAfterPtrInt
    json_bug_test.go:40: 
        	Error Trace:	/Users/jeka/Veeam/workbench/projects/cast/internal/rm/casedata/json_bug_test.go:40
        	Error:      	Not equal: 
        	            	expected: "{\"c\":{\"v\":0}}"
        	            	actual  : "{}"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-{"c":{"v":0}}
        	            	+{}
        	Test:       	TestZeroFirstByteAfterPtrInt
--- FAIL: TestZeroFirstByteAfterPtrInt (0.00s)

Expected :{"c":{"v":0}}
Actual   :{}
<Click to see difference>


=== RUN   TestNonZeroFirstByteAfterPtrInt
--- PASS: TestNonZeroFirstByteAfterPtrInt (0.00s)
=== RUN   TestZeroFirstByteAfterPtrBool
    json_bug_test.go:58: 
        	Error Trace:	/Users/jeka/Veeam/workbench/projects/cast/internal/rm/casedata/json_bug_test.go:58
        	Error:      	Not equal: 
        	            	expected: "{\"c\":{\"v\":false}}"
        	            	actual  : "{}"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-{"c":{"v":false}}
        	            	+{}
        	Test:       	TestZeroFirstByteAfterPtrBool
--- FAIL: TestZeroFirstByteAfterPtrBool (0.00s)

Expected :{"c":{"v":false}}
Actual   :{}
<Click to see difference>


=== RUN   TestNonZeroFirstByteAfterPtrBool
--- PASS: TestNonZeroFirstByteAfterPtrBool (0.00s)
=== RUN   TestZeroFirstByteAfterPtrString
    json_bug_test.go:76: 
        	Error Trace:	/Users/jeka/Veeam/workbench/projects/cast/internal/rm/casedata/json_bug_test.go:76
        	Error:      	Not equal: 
        	            	expected: "{\"c\":{\"v\":\"\"}}"
        	            	actual  : "{}"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-{"c":{"v":""}}
        	            	+{}
        	Test:       	TestZeroFirstByteAfterPtrString
--- FAIL: TestZeroFirstByteAfterPtrString (0.00s)

Expected :{"c":{"v":""}}
Actual   :{}
<Click to see difference>


=== RUN   TestNonZeroFirstByteAfterPtrString
--- PASS: TestNonZeroFirstByteAfterPtrString (0.00s)
FAIL

I thik problem is here

go-json/internal/encoder/vm/vm.go

Line 585 in df897ae

if p == 0 || (ptrToPtr(p) == 0 && (code.Flags&encoder.IsNextOpPtrTypeFlags) != 0) {

ptrToPtr(p) in this case return not a pointer but value

[JekaNS]

Same bug with empty string. I've updated the test code and result in the first post.

Also I tried this on different architectures. Bug is reproduced on all of them:

• go version go1.20.1 linux/amd64
• go version go1.21.6 linux/arm64
• go version go1.21.3 darwin/arm64