Add Slovenia (SI) tax regime by daesparza02 · Pull Request #893 · invopop/gobl

daesparza02 · 2026-07-03T13:26:20Z

This PR adds Slovenia (SI) as a new tax regime.

I picked Slovenia because it wasn't supported yet and fits GOBL's model well: an EU member
state using EUR, with tax identifiers that carry real modulo-11 check digits, so the regime
can do genuine validation rather than only format checks. I used the Netherlands (nl)
regime as a structural reference, since it's close to Slovenia: EU member, EUR, and a VAT
identity with a checksum.

What's included

Base regime: EUR, Europe/Ljubljana, the standard invoice scenarios, and credit notes for corrections.
VAT rates: the standard rate with its history (20% since 2002, 22% from 1 July 2013), plus the current reduced rate (9.5%) and the special reduced rate of 5% for books, newspapers and periodicals.
Tax ID validation: the modulo-11 check-digit algorithm, applied to two identifiers — the VAT number / davčna številka (8 digits) and the domestic registration number / matična številka (10 digits).
Invoice rule: the supplier must carry a tax ID code. The registration number identifies a company but is not a substitute for the VAT number on an invoice, so the rule checks specifically for the tax ID (ZDDV-1, Article 82).

Scope and design notes

A few things I decided deliberately, with the reasoning in case it helps the review:

I modelled the full date history only for the standard rate, to exercise the Since mechanism. The reduced rates have been stable for years, so I kept only their current values rather than pad the base regime with historical data — happy to add the full history if you'd prefer.
The modulo-11 logic lives in one place (tax_identity.go) and takes the weights as a parameter, since the two identifiers share the same scheme with different weights. The registration-number check strips its three-digit branch suffix (which has no check digit of its own) and reuses it.
One Slovenian detail worth flagging: a remainder of 0 is never assigned (no valid number produces it), so the shared validator rejects it explicitly.
I kept the scope to tax and identity rules — Slovenia's own e-invoicing formats and networks are a separate kind of extension in GOBL, so I left those out.

Testing

Table-driven tests across the package: 5 test functions, 29 sub-cases, covering valid and invalid inputs.
The official sources publish the number formats but not the check-digit formulas, so I verified each checksum against a real, public identifier from the same company (Krka d.d.: VAT number SI82646716 and registration number 5043611000) and exercised every branch of both algorithms, including the remainder == 0 case that can never yield a valid number.
gofmt, go vet and golangci-lint are clean.

Sources

VAT rates — Financial Administration of the Republic of Slovenia (FURS), and the European Commission rates table
https://www.fu.gov.si/en/taxes_and_other_duties/areas_of_work/value_added_tax_vat
https://taxation-customs.ec.europa.eu/system/files/2021-06/vat_rates_en.pdf
Invoice requirements — SPOT business portal (ZDDV-1, Article 82)
https://spot.gov.si/en/info/accountancy/invoicing
Tax number format — FURS
https://www.fu.gov.si/en/taxes_and_other_duties/work_with_us/entry_into_the_tax_register_and_tax_number
Registration number (matična številka) format — PISRS, Article 11 of the Business Register decree
https://pisrs.si/Pis.web/pregledPredpisa?id=URED7599
Checksum algorithms — the official registers document the formats but not the formulas, so I
based them on a widely used open-source implementation (python-stdnum) and verified them
against the public identifiers above:
https://github.com/arthurdejong/python-stdnum

Pre-Review Checklist

codecov · 2026-07-06T17:41:05Z

Codecov Report

❌ Patch coverage is 95.68345% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.73%. Comparing base (458d352) to head (cdb8fc1).

Files with missing lines	Patch %	Lines
regimes/si/tax_identity.go	86.04%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main     #893    +/-   ##
========================================
  Coverage   94.73%   94.73%            
========================================
  Files         316      320     +4     
  Lines       17198    17337   +139     
========================================
+ Hits        16292    16425   +133     
- Misses        560      563     +3     
- Partials      346      349     +3

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# Conflicts: # CHANGELOG.md

samlown

Thanks! A few style changes for the rule handling required.

samlown · 2026-07-13T13:10:25Z

+			is.InContext(tax.RegimeIn(CountryCode)),
+			rules.Field("supplier",
+				rules.Assert("01", "invoice SI supplier must have a tax ID code",
+					is.Func("has tax ID code", hasSupplierTaxIDCode),


Its better to use direct rule checks here instead of a helper.

Done — replaced the helper with direct nested field rules using is.Present on tax_id and code.

samlown · 2026-07-13T13:10:47Z

+		},
+		Sources: []*cbc.Source{
+			{
+				Title: i18n.NewString("Uredba o vodenju in vzdrževanju Poslovnega registra Slovenije"),


Missing English translation.

Fixed, the source title now carries both English and Slovenian.

samlown · 2026-07-13T13:12:03Z

+	// IdentityTypeMaticna represents the Slovenian registration number
+	// (matična številka) assigned by AJPES to every entity entered in
+	// the Slovenian Business Register (e.g. "5043611000").
+	IdentityTypeMaticna cbc.Code = "MATICNA"


Best to avoid local names in variables, there is likely to be a good translation. I'd also question the MATICNA code itself, it looks like a name that's been capitalized as opposed to a name, I'd expect there to be some type of abbreviated version.

I changed the code from the spelled-out word to MŠ, the official Slovenian abbreviation for matična številka. f you'd rather avoid the non-ASCII character, I'm happy to use an ASCII form (MS).

samlown · 2026-07-13T13:12:51Z

+				org.IdentityTypeIn(IdentityTypeMaticna),
+				rules.Field("code",
+					rules.Assert("01", "identity code for type MATICNA must be valid",
+						is.Func("valid", isValidRegistrationNumber),


Checks here could be split up to help users differentiate between length and check digit.

Done, split into three separate rules: presence, format and the check digit. Each failure now reports its own code and message.

samlown · 2026-07-13T13:14:07Z

+func validateTaxCode(code cbc.Code) error {
+	if code == "" {
+		return nil
+	}
+	if len(code) != taxCodeLen {
+		return errors.New("invalid length")
+	}
+	if code[0] == '0' {
+		return errors.New("invalid format")
+	}
+	return validateMod11(code, taxCodeMultipliers)
+}


These errors will never reach anywhere, so the checks should probably be split into separate rules.

Done, removed validateTaxCode and split it into two rules: a format check (01) using a regex that covers length, digits and the non-zero first digit, and the check digit (02).

samlown · 2026-07-13T13:15:20Z

+// assigned (no valid number produces it), a remainder of 1 means a check
+// digit of 0, and any other remainder means a check digit of 11 minus the
+// remainder.
+func validateMod11(code cbc.Code, weights []int) error {


Again, for a private method, the errors returned are not useful.

Done, validMod11 now returns a bool rather than building error values that were discarded; the user-facing message lives in the check-digit rule.

daesparza02 · 2026-07-14T07:25:47Z

Thanks for the thorough review, Sam — really helpful. I've addressed all the points: split the identifier validation into separate format/check-digit rules with distinct codes, switched the invoice rule to direct field checks, and cleaned up the naming and translations.

daesparza02 added 2 commits July 3, 2026 14:33

Add Slovenia (SI) tax regime

5239a83

Add Slovenia (SI) invoice example

7c2163a

daesparza02 marked this pull request as ready for review July 3, 2026 13:32

samlown added the regime Related to a specific regime. label Jul 6, 2026

Merge remote-tracking branch 'upstream/main' into add-si-regime

cdb8fc1

# Conflicts: # CHANGELOG.md

samlown requested changes Jul 13, 2026

View reviewed changes

si: address review feedback

73843df

daesparza02 requested a review from samlown July 14, 2026 07:28

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What's included

Scope and design notes

Testing

Sources

Pre-Review Checklist

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daesparza02 commented Jul 14, 2026

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daesparza02 commented Jul 3, 2026 •

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