[Bug]: Support for ISO 9362:2022 BIC (SWIFT) codes

[fira42073]

Problem
The built-in bic validator currently appears to reject some valid BICs introduced under the ISO 9362:2022 revision — specifically those where the first four characters of the party prefix can include digits (e.g. E097AEXX).

This pattern is valid per ISO 9362:2022, section 6.3.1, which allows the party prefix to be alphanumeric, not just letters.

Example

type Bank struct {
    SwiftCode string `validate:"bic"`
}

bank := Bank{SwiftCode: "E097AEXX"} // Valid under ISO 9362:2022
err := validate.Struct(bank)

Currently, this fails validation with the built-in bic tag.

Expected behavior
The bic tag should validate codes conforming to both:
ISO 9362:2014 (legacy 8- or 11-char codes), and
ISO 9362:2022 (new alphanumeric party prefix).

References
ISO 9362:2022 (Business Identifier Code)
Example real-world BIC: E097AEXX
Related discussion: Symfony issue 51975

I'm willing to contribute here.

[fira42073]

Apparently this is the regex string

bicRegexString                   = `^[A-Za-z]{6}[A-Za-z0-9]{2}([A-Za-z0-9]{3})?$`

changing it to the following one should fix the problem

bicRegexString                   = `^[A-Z0-9]{4}[A-Z]{2}[A-Z0-9]{2}(?:[A-Z0-9]{3})?$`

But I cannot say I'm a pro at regex, so please someone double check this C:

[nodivbyzero]

@fira42073 PRs are always welcome! Just open one with an updated unit test for the new ISO 9362:2022 revision.

[fira42073]

I've opened the PR with the test and potential fix to the regex, but it started matching S23CKENXXXX as valid bic code, so I changed ^[A-Z0-9]{4}[A-Z]{2}[A-Z0-9]{2}(?:[A-Z0-9]{3})?$ to ^(?:[A-Z]{4}|[A-Z][0-9]{3})[A-Z]{2}[A-Z0-9]{2}(?:[A-Z0-9]{3})?$. However I am not sure if the test was correct or regex. Maybe that bic used to be invalid under 2014 and under 2022 it's valid, or the regex was not strict enough. To be honest this requires further research and some banking experts, because I don't have an access to the specification itself, it's not open. At the very least, there is the test with a valid bic that belongs to a bank in MENA region in the PR, so I hope that's useful

[fira42073]

Aight, upon some extensive research, S23CKENXXXX is valid under ISO 9362:2022.
Regarding the pattern: we should stick with with previously mentioned ^[A-Z0-9]{4}[A-Z]{2}[A-Z0-9]{2}(?:[A-Z0-9]{3})?$. The alternative ^(?:[A-Z]{4}|[A-Z][0-9]{3})… is too restrictive and would wrongly reject valid mixes like S23C, A1B2, 1AB3, etc.