Duplicate key allowed in inline table

[moorereason]

Describe the bug
Given e={b=1,b=4}, go-toml returns the following (using gotoml-test-decoder):

{
  "e": {
    "b": {
      "type": "integer",
      "value": "4"
    }
  }
}

To Reproduce
https://play.golang.org/p/by7ih3epoCp

toml.Unmarshal([]byte("e={b=1,b=4}"), &v)

Expected behavior
I expected an error. The TOML spec says:

Defining a key multiple times is invalid.

BurntSushi returns an error of Key 'e.b' has already been defined.

Versions

• go-toml: 11f789e
• go version devel go1.18-6294207a1c7 Tue Oct 19 15:03:39 2021 +0000 linux/amd64

Additional context
Found while doing differential fuzzing against BurntSushi.

[moorereason]

Once this is fixed, we can regen the toml-test files to include toml-lang/toml-test#93.

[pelletier]

Started working on this, but realized there is some part of the spec that is unclear to me: toml-lang/toml#848 (comment).

Let me know if you have any thoughts on how we should handle dotted keys in inline tables!

[moorereason]

My take:

1. Dotted keys within a table definition should be treated the same regardless of the type of table (standard or inline).
2. Dotted keys within a table are acceptable so long as the sub-tables are fully defined within the current table context. That clarification appears to be the point of the toml PR referenced above.

[pelletier]

👍🏻 Went with that interpretation until they chime in.

[pelletier]

Regenerated the toml-test files to include the new test. Let me know if i've missed anything.