Add Australia GST regime

[albipuliga]

Australia GST regime

• Australia is modeled as a GST regime with a 10% standard rate.
• GST-free supplies map to the shared GST zero key.
• Input-taxed supplies map to the shared GST exempt key.
• The regime models ABN as the AU tax identity. ACN display obligations are treated as a separate corporate-document concern and are not modeled here as the primary tax identifier.
• ABN validation follows the ABR checksum algorithm for 11-digit ABNs.
• Invoice validation requires supplier details and ABN, and currently requires customer identification for invoices of AUD 1,000+ and self-billed invoices.
• Electronic invoicing references align with Peppol PINT A-NZ BIS.

Open question

AU tax invoice rules for invoices of AUD 1,000+ allow identifying the customer by the customer's identity OR ABN. The current implementation requires customer.name in that case, which aligns with existing shared invoice validation in bill/invoice.go. I did not broaden this PR to change the shared validation model, but I'd love some feedback on whether AU should support customer.tax_id.code without customer.name, and if so, whether that should be handled at regime level or by adjusting the shared invoice validator.

Sources

• ATO - GST
• ATO - Tax invoices
• ABR - ABN format
• Peppol PINT A-NZ BIS

Pre-Review Checklist

• Opened this PR as a draft
• Read the CONTRIBUTING.md guide.
• Performed a self-review of my code.
• Added thorough tests with at least 90% code coverage.
• Modified or created example GOBL documents to show my changes in use, if appropriate.
• Added links to the source of the changes in tax regimes or addons, either structured or in the comments.
• Run go generate . to ensure that the Schemas and Regime data are up to date.
• Reviewed and fixed all linter warnings.
• Been obsessive with pointer nil checks to avoid panics.
• Updated the CHANGELOG.md with an overview of my changes.
• Marked this PR as ready for review.

And if you are part of the org:

• Requested a review from Copilot and fixed or dismissed (with a reason) all the feedback raised.
• Requested a review from @samlown.

[claude]

Claude Code Review

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.17%. Comparing base (e36c17e) to head (1e2da5a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #784      +/-   ##
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+ Coverage   93.11%   93.17%   +0.06%     
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  Files         334      338       +4     
  Lines       18086    18265     +179     
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+ Hits        16840    17019     +179     
  Misses        876      876              
  Partials      370      370              

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[Copilot]

Pull request overview

Adds a new Australian (AU) tax regime to the GOBL regimes registry, modeling Australia as a GST regime with ABN (Australian Business Number) identity handling and AU-specific invoice validation rules.

Changes:

• Register new AU regime and generate supporting regime/schema data.
• Implement ABN validation (ABR checksum) + normalization behavior via shared tax identity normalization.
• Add AU invoice validation rules around supplier ABN requirements and customer identification threshold/self-billed handling, plus examples and tests.

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
regimes/regimes.go	Registers the new au regime package so it’s available via the global regime registry.
regimes/au/au.go	Defines the AU regime metadata (GST scheme, sources, timezone, corrections) and hooks validator/normalizer.
regimes/au/tax_categories.go	Introduces AU GST category using global GST keys and a 10% general rate since 2000-07-01.
regimes/au/tax_identity.go	Adds ABN checksum validation logic for AU tax identities.
regimes/au/bill_invoice.go	Adds AU-specific invoice validation (supplier details/ABN, customer identification threshold, self-billed rules).
regimes/au/README.md	Documents the AU regime model, ABN algorithm, GST mapping, and invoice rules.
regimes/au/au_test.go	Tests regime definition integrity and correction options schema output.
regimes/au/tax_identity_test.go	Tests ABN validation and normalization expectations.
regimes/au/bill_invoice_test.go	Tests AU invoice validation behavior for threshold/self-billed and supplier constraints.
examples/au/invoice-au-au.yaml	Adds an AU example invoice input document.
examples/au/out/invoice-au-au.json	Adds generated AU example invoice output envelope.
data/schemas/tax/regime-code.json	Adds AU as a valid regime code in the published JSON schema.
data/regimes/au.json	Adds generated serialized regime definition for AU.
CHANGELOG.md	Notes the addition of the Australian GST regime.

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[Copilot]

strconv.Atoi(normalized) is being used only to assert the ABN is numeric, but it can fail for valid 11-digit ABNs on 32-bit platforms due to integer overflow. Prefer a digit-only check (iterate runes/bytes) or strconv.ParseUint(normalized, 10, 64) to avoid rejecting valid ABNs.

[Copilot]

The test case name says "at threshold", but with Item.Price = 1000.00 and 10% GST the invoice Totals.TotalWithTax becomes 1100.00 (above the 1000.00 threshold). Either adjust the amount so TotalWithTax is exactly 1000.00, or rename the test to reflect it’s testing the >= threshold branch.

[Copilot]

The Markdown tables use a double leading pipe (|| ...) which creates an extra empty first column in most renderers. Consider changing these rows to a single leading | so the table renders as intended (e.g., | Position | 1 | 2 | ... |).

[Copilot]

Same table formatting issue here: rows start with || (double pipe), which will render an unintended blank first column. Update to a single leading | for proper Markdown table formatting.

[Copilot]

The rate table also starts rows with ||, which most Markdown renderers interpret as an empty first column. Use a single leading | for these rows as well.