fix(core):fix missing info of flattened_errors

[lhanjian]

Summary

When a nested configuration error occurs, a more precise and identifiable description is required
When nested configuration conflicted occurs, it returns the desired flatterned error

Please see the test cases for details of the problem

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix FTI-6351/FTI-6318

[CLAassistant]

All committers have signed the CLA.

[outsinre]

Seems the error message is always string?

[lhanjian]

@outsinre maybe nil, or table.

err_t[ref.field] just like field_err_t

[outsinre]

If parent_idx is nil, then tostring(parent_idx) is true.

[lhanjian]

@outsinre
i think tostring(nil) maybe nil?

[outsinre]

The printed nil is a string, not the Lua nil.

[outsinre]

The errs_item_name and entity on this line refer to the same thing?

[lhanjian]

@outsinre no.

entity is its original name.
errs_item_name is key name of errs

[outsinre]

The 400 error is due to DB-less by default does not support this kind of format. DB-less uses declarative format that needs all entities flattened at top-level.

It expects the snis not nested within the certificates.

[flrgh]

Hmm 🤔 I don't know if it's possible to properly flatten errors in this case, because the result we get from the declarative validator is ambiguous. Consider this input:

{
  _format_version = "3.0",
  consumers = {
    {
      username = "consumer-01",
      basicauth_credentials = {
        { username = "user-01", password = "pwd" },
        { username = "user-11", password = "pwd" },
        { username = "user-02", password = "pwd" },
        { username = "user-11", password = "pwd" },
      }
    },
    {
      username = "consumer-02",
      basicauth_credentials = {
        { username = "user-99", password = "pwd" },
      }
    },
    {
      username = "consumer-03",
      basicauth_credentials = {
        { username = "user-01", password = "pwd" },
        { username = "user-33", password = "pwd" },
        { username = "user-02", password = "pwd" },
        { username = "user-33", password = "pwd" },
      }
    }
  }
}

It has the following duplicates:

1. consumers[1].basicauth_credentials[4] (user-11)
2. consumers[3].basicauth_credentials[1] (user-01)
3. consumers[3].basicauth_credentials[3] (user-02)
4. consumers[3].basicauth_credentials[4] (user-33)

The error table we receive from :parse_table() looks like this:

{
  basicauth_credentials = {
    [1] = "uniqueness violation: 'basicauth_credentials' entity with username set to 'user-01' already declared",
    [3] = "uniqueness violation: 'basicauth_credentials' entity with username set to 'user-02' already declared",
    [4] = "uniqueness violation: 'basicauth_credentials' entity with username set to 'user-33' already declared",
  },
}

1. The declarative code actually overwrote the error in consumers[1].basicauth_credentials[4] with the error in consumers[3].basicauth_credentials[4] (presumably because they both happened at index 4)
2. We cannot use this information to determine which consumer each basicauth_credentials error corresponds to

In summary, I don't think this can be fixed in the error-flattening code alone. A fix within kong.db.schema.others.declarative_config must be made first.

[lhanjian]

@flrgh
I try to add your inputs to test case, it can get 4 results.

Is this what you need?

[flrgh]

I actually fixed a very similar issue back in #12797. The problem is the fix was only applied for primary key errors, whereas the basicauth_credentials.username case is a unique field and not a primary key. I've applied the fix in #14017.

[outsinre]

There are two errors in this case.

1. The basicauth_credentials error caused by

   kong/kong/db/schema/init.lua

   Line 1504 in 358fff3

   local ok, err = mutually_required(needs_changed and original_input or input, args)

   but swallowed by

   kong/kong/db/schema/others/declarative_config.lua

   Line 792 in 358fff3

   if not ok then

   We'd better merge the two errors table.

2. The snis error caused by

   kong/kong/db/schema/init.lua

   Line 2134 in 358fff3

   errors[name] = validation_errors.REQUIRED

The root cause is that DB-less mode expects flattened declarative format as stated here: #13998 (comment).