toml: cannot decode TOML array table into struct field

[xulimeng3306]

Describe the bug When using version 2.0.0, the following structure can be parsed as a map. When using version 2.1.0, it will be judged as an array structure, resulting in a parsing error.

To Reproduce Steps to reproduce the behavior. Including TOML files.

package main

import (
	"fmt"

	tomlv2 "github.com/pelletier/go-toml/v2"
)
type Config struct {
	A A `toml:"A" yaml:"A"`
}

type A map[string]struct {
	C     int  `toml:"C"`
	D     int  `toml:"D"` // 走老接口
	Body1 Body `toml:"E"`
	Body2 Body `toml:"G"`
}

// WhiteList 白名单配置
type Body struct {
	F string `toml:"F"`
}

var data2 = `
[A]
[[A.B]]
  C = 100
[[A.B]]
  D = 0
[[A.B.E]]
  F = "123215320,10286292"
[[A.B.G]]
  F = ""
`

func main() {
	newConf := Config{}
	err := tomlv2.Unmarshal([]byte(data2), &newConf)
	fmt.Println(newConf, err)
}

Expected behavior A clear and concise description of what you expected to happen, if other than "should work".

Versions

• go-toml: 2.1.0 (git sha)
• go: go1.21
• operating system: Linux

Additional context Add any other context about the problem here that you think may help to diagnose.

[moorereason]

Bisected. This behavior changed in https://github.com/pelletier/go-toml/commit/7baa23f493a82b3f24f4dada5d0b02d17fbde175.

[pelletier]

Unless I've missed something, this error is normal (and what was corrected in the fix @moorereason highlighted). The notation [[...]] in TOML indicates an array of table. It defines a new table in a list of table. As a result, the containing key must be a slice or an array.

The version before https://github.com/pelletier/go-toml/commit/7baa23f493a82b3f24f4dada5d0b02d17fbde175 was erroneously accepting input that didn't match that structure.

I've modified the A type in the example to match the provided data: https://go.dev/play/p/KywHmXIjURW

[pelletier]

Closing this as it's been over a month and the issue seems understood. Feel free to re-open if there is still a problem!