Incorrect indentation for arrays of custom types

[daniel-weisse]

Describe the bug
Using the SetIndentTables(true) option does not correctly indent keys of arrays of custom types.
It does work correctly if the custom type is not a slice.
Example:
If I have some data structure a.b.c I expect the generated TOML to look like the following:

# comment A
[A]
  # comment B
  [A.B]
    # comment C
    [A.B.C]

Assuming c is an array I would expect the following:

# comment A
[A]
  # comment B
  [A.B]
    # comment C
    [[A.B.C]]
      # Entry 1
    [[A.B.C]]
      # Entry 2

Instead, go-toml gives me something like the following:

# comment A
[A]
  # comment B
  [A.B]
    # comment C
[[A.B.C]]
      # Entry 1
[[A.B.C]]
      # Entry 2

To Reproduce

package main

import (
	"bytes"
	"fmt"

	toml "github.com/pelletier/go-toml/v2"
)

func main() {
	cfg := layer0{
		Value: "value",
		Layer1: []layer1{
			{
				Value: "value",
				Layer2: []layer2{
					{
						Value: "value",
						Layer3: []layer3{
							{
								Value: "value",
								CustomType: customType{
									Value: "value",
								},
							},
						},
					},
				},
			},
		},
	}

	buf := bytes.Buffer{}
	enc := toml.NewEncoder(&buf).
		SetIndentTables(true).
		SetIndentSymbol("+") // Using "+" as indent symbol for easier comparison
	if err := enc.Encode(cfg); err != nil {
		panic(err)
	}

	fmt.Println(buf.String())
}

type layer0 struct {
	Value  string   `toml:"value" comment:"value comment"`
	Layer1 []layer1 `toml:"layer1" comment:"layer1 comment"`
}

type layer1 struct {
	Value  string   `toml:"value" comment:"value comment"`
	Layer2 []layer2 `toml:"layer2" comment:"layer2 comment"`
}

type layer2 struct {
	Value  string   `toml:"value" comment:"value comment"`
	Layer3 []layer3 `toml:"layer3" comment:"layer3 comment"`
}

type layer3 struct {
	Value      string     `toml:"value" comment:"value comment"`
	CustomType customType `toml:"customType" comment:"customType comment"`
}

type customType struct {
	Value string `toml:"value" comment:"value comment"`
}

Expected behavior
I'm expecting the generated TOML to look like the following, correctly indenting layer1.layer2 with + and layer1.layer2.layer3 with two ++:

$ go run ./
# value comment
value = 'value'

# layer1 comment
[[layer1]]
+# value comment
+value = 'value'

+# layer2 comment
+[[layer1.layer2]]
++# value comment
++value = 'value'

++# layer3 comment
++[[layer1.layer2.layer3]]
+++# value comment
+++value = 'value'

+++# customType comment
+++[layer1.layer2.layer3.customType]
++++# value comment
++++value = 'value'

In practice, only the comments for layer1.layer2 and layer1.layer2.layer3 are indented, the keys are not:

$ go run ./
# value comment
value = 'value'

# layer1 comment
[[layer1]]
+# value comment
+value = 'value'

+# layer2 comment
[[layer1.layer2]]
++# value comment
++value = 'value'

++# layer3 comment
[[layer1.layer2.layer3]]
+++# value comment
+++value = 'value'

+++# customType comment
+++[layer1.layer2.layer3.customType]
++++# value comment
++++value = 'value'

Versions

• go-toml: v2.2.0
• go: 1.22.1
• operating system: Linux

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

[pelletier]

Thank you for the detailed issue report!