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Dispatch No. 04 · Engineering
Golden Master Testing: How We Port WordPress PHP Functions to Rust with 100% Parity
WordPress's formatting and slug functions have twenty years of quirky edge cases. Guessing how they behave breaks permalinks. Here is how our Golden Master verification loop guarantees exact parity.
Plate II — The Typecase
Field Dispatch #19
Author's Note
Billy is the founder and lead systems engineer of Neopress. Writing from the intersection of native Rust infrastructure, legacy WordPress migration, and AI-assisted visual publishing.
Edge cases hide in twenty-year-old regexes
Take sanitize_title_with_dashes or wpautop in WordPress core. On the surface, turning a post title into a URL slug or wrapping paragraphs in <p> tags sounds trivial. In practice, millions of existing URLs depend on exact UTF-8 accent stripping, HTML entity handling, nested shortcode boundaries, and preserve-block rules accumulated since WordPress 1.5.
If Neopress generates a slightly different slug during a migration, an existing link from search engines or a newsletter 404s. Good enough is not good enough.
Never guess what legacy PHP does when you can execute the real PHP function, capture its exact output, and lock it in as a Rust unit test.
The Golden Master PHP-to-Rust loop
In our workspace (crates/neopress-transpiler and crates/generated_slugify), every transpiled WordPress function follows a strict 4-step verification loop:
- Step 1 — Reference PHP Execution: We run
generate_golden_master.phpagainst real PHP to produce a deterministicgolden_master.jsonfixture covering hundreds of edge-case inputs (accented UTF-8, malformed HTML, nested shortcodes, zero-width spaces). - Step 2 — Rust Port: We implement the pure Rust equivalent with zero unsafe byte slicing.
- Step 3 — Automated Parity Harness:
cargo test --workspacedeserializesgolden_master.jsonand asserts that the Rust output matches the PHP output on every single vector.
/n-admin/post — Editing posts with deterministic slug generation and SEO metadata
