metadata.Keys (and thus metadata.Undecoded) is invalid in some cases

[maroux]

Sample code:

package main

import (
	"fmt"

	"github.com/BurntSushi/toml"
)

func main() {
	content := `[table.subtable.subsubtable]
a = 1
b = 2
`
	var v interface{}
	metadata, err := toml.Decode(content, &v)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%#v\n", metadata.Keys())
}

Playground: https://go.dev/play/p/Rr5bm5DbEql

Output:

[]toml.Key{toml.Key{"table", "subtable", "subsubtable"}, toml.Key{"table", "subtable", "subsubtable", "b"}, toml.Key{"table", "subtable", "subsubtable", "b"}}

Notice how the second and third value in that slice both point to b.

Expected output:

[]toml.Key{toml.Key{"table", "subtable", "subsubtable"}, toml.Key{"table", "subtable", "subsubtable", "a"}, toml.Key{"table", "subtable", "subsubtable", "b"}}

The root cause seems to be somewhere near this append call. The result of append can return a slice backed by the same array if the capacity is available. See Go example code: https://go.dev/play/p/2FGKuCvCUKz.

[maroux]

I've opened 2 PRs with 2 possible fixes for this bug.

[im-alex07]

Output:

[]toml.Key{toml.Key{"table", "subtable", "subsubtable"}, toml.Key{"table", "subtable", "subsubtable", "b"}, toml.Key{"table", "subtable", "subsubtable", "b"}}

Notice how the second and third value in that slice both point to b.

I also encountered this bug. Please fix it.