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cmd/compile: struct field tag not working when use generics #48317

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nzlov opened this issue Sep 10, 2021 · 2 comments
Closed

cmd/compile: struct field tag not working when use generics #48317

nzlov opened this issue Sep 10, 2021 · 2 comments
Labels
FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Milestone
Go1.18

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@nzlov
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nzlov commented Sep 10, 2021 •
edited

What version of Go are you using (go version)?

$ go version
go version devel go1.18-c69f5c0d76 Fri Sep 10 10:45:59 2021 +0000 darwin/amd64

Does this issue reproduce with the latest release?

No

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/nzlov/Library/Caches/go-build"
GOENV="/Users/nzlov/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/nzlov/workspace/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/nzlov/workspace/go"
GOPRIVATE=""
GOPROXY="https://goproxy.cn,direct"
GOROOT="/Users/nzlov/program/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/nzlov/program/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="devel go1.18-c69f5c0d76 Fri Sep 10 10:45:59 2021 +0000"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/nzlov/workspace/vgo/generices/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/71/4t6lk06x5y77f2wyln9vqnlw0000gn/T/go-build147050757=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

import (
	"encoding/json"
	"fmt"
)

type A[T any] struct {
	Name string `json:"name"`
	Data T `json:"d"`
	ErrResp ErrResp `json:"errorResponse"`
}

type ErrResp struct {
	Age int `json:"age"`
}

func main() {
	fmt.Printf("%+v\n", *a[int]())
}

func a[T any]() *T {

	data :=`{"name":"name","d":1,"errorResponse":{"age":10}}`
	a1 := A[T]{}
	 err := json.Unmarshal([]byte(data), &a1)
	if err!=nil{
		panic(err)
	}
	fmt.Printf("%+v\n",a1)
	return &a1.Data
}

What did you expect to see?

{Name:name Data:1 ErrResp:{Age:10}}

What did you see instead?

{Name:name Data:0 ErrResp:{Age:0}}

Fix:

  1. use env GOEXPERIMENT=unified
  2. return Unmarshal obj. like ex1
  3. use full field name. like ex2

Work examples:

package main

import (
	"encoding/json"
	"fmt"
)

type A[T any] struct {
	Name string `json:"name"`
        Data T `json:"d"`
	ErrResp ErrResp `json:"errorResponse"`
}

type ErrResp struct {
	Age int `json:"age"`
}

func main() {
	fmt.Printf("%+v\n", *a[int]())
}

func a[T any]() *A[T] {
	data :=`{"name":"name","d":1,"errorResponse":{"age":10}}
	a1 := A[T]{}
	err := json.Unmarshal([]byte(data), &a1)
	if err!=nil{
		panic(err)
	}
	fmt.Printf("%+v\n",a1)
	return &a1  // <---- return Unmarshal obj
}

package main

import (
	"encoding/json"
	"fmt"
)

type A[T any] struct {
	Name string `json:"name"`
        Data T `json:"data"`
	ErrorResponse ErrResp `json:"errorResponse"`  // <---- use full name
}

type ErrResp struct {
	Age int `json:"age"`
}

func main() {
	fmt.Printf("%+v\n", *a[int]())
}

func a[T any]() *T {

	data :=`{"name":"name","data":1,"errorResponse":{"age":10}}`
 	a1 := A[T]{}
 	err := json.Unmarshal([]byte(data), &a1)
 	if err!=nil{
		panic(err)
 	}
 	fmt.Printf("%+v\n",a1)
 	return &a1.Data
}
@nzlov nzlov changed the title encoding/json: struct field tag no work encoding/json: struct field tag no work when use generic Sep 10, 2021
@gopherbot
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Change https://golang.org/cl/349013 mentions this issue: cmd/compile: save the note of fields when translating struct

@thanm thanm added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Sep 10, 2021
@thanm thanm added this to the Go1.18 milestone Sep 10, 2021
@thanm
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thanm commented Sep 10, 2021

@randall77 @danscales

@dsnet dsnet changed the title encoding/json: struct field tag no work when use generic cmd/compile: struct field tag not working when use generics Sep 11, 2021
@golang golang locked and limited conversation to collaborators Sep 13, 2022
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