khosra/docs/conventions.md

Conventions

The style floor. Do not ask about anything here — read it and comply. Disagreement is legitimate but goes through an ADR, not a diff.

Language and dependencies

• Go, current stable release. Stdlib first, every time.
• net/http, html/template, log/slog, os, io/fs, embed. Routing is http.ServeMux with Go 1.22+ patterns — GET /{section}/{slug}/ and {path...} for multi-segment slugs — so no router library is needed. No web framework, ORM, or config library — flags plus environment variables, parsed in one place. The site root (-site, ATELIER_SITE) is the only required setting; default templates are embedded so a bare site root renders (ADR-0011).
• New dependency = ADR + human approval + scripts/allowed-deps.txt. verify.sh enforces it.
• Prefer 40 lines of obvious code over a dependency doing it in one call — unless the 40 lines would be subtly wrong in cases the author cannot predict, which is why YAML is a dependency (ADR-0020).

Package layout

cmd/atelier/      main, flag parsing, explicit wiring — the only place things are assembled
internal/content/ bundles, frontmatter, slugs, queries — knows the disk, not HTTP
internal/render/  markdown, transforms, templates — knows content, not HTTP
internal/web/     handlers, routing, headers, caching — knows both, exposes neither
internal/ext/     extensions, one package each — earned at its counter (see extensions.md)

Dependencies point inward. internal/content imports nothing from the others; cmd imports everything and is imported by nothing. A feature under internal/ext/ may import internal/content and internal/render, and must not import internal/web, cmd/, or another feature — sibling imports are what make an agent's read set compound (ADR-0027). Every internal/ext/* package carries a doc.go; verify.sh fails without one. Routes reach web by assembly in cmd/atelier/wire.go, so web never learns features exist. No utils, helpers, common, shared, manager, base, impl, core — a package name not describing a domain is a smell. Flat until a package exceeds FILE_LOC_WARN; do not pre-partition, and a single-file package therefore warns at the same point it wants splitting.

Naming and shape

• Functions under FUNC_LOC_WARN, ideally under 20. Nesting depth under 4. File length is not a target: one coherent file beats two split to satisfy a counter. Values: scripts/budgets.env.
• No init(). No package-level mutable state. No singletons. Wire explicitly in cmd.
• Accept interfaces only where a second implementation exists; return concrete types.
• ctx context.Context first when a call can block or be cancelled — not decoratively.
• Never call time.Now() outside a clock.go. A render that reads the clock is only true for a while, and an injected accessor is what makes that expressible later; verify.sh fails on any other caller, because a forgotten expiry serves staleness silently.
• Comments explain why, never what. Delete a comment narrating the next line. One stating a non-obvious invariant is worth ten describing control flow.

Documentation

Written for a maintainer working alone, years from now, with no agent to explain anything. verify.sh fails on a missing package comment and on a citation naming an ADR that does not exist; a missing doc comment on an exported identifier is a warning, because no gate can tell // Load loads. from a useful sentence, and a gate whose cheapest satisfaction is noise buys noise.

• Every package has a package comment. What it owns, what it does not, and which packages may import it. For internal/ext/* that is the four-line doc.go shape in extensions.md.
• Every exported identifier has a doc comment (warned, not gated). The exported surface of a 2000-line core is small, and go doc ./... is the only navigation tool that still works when nothing else does. A comment that restates the name (// Load loads.) is worse than none: say what it returns on absence, what it costs, what it assumes.
• Cite the ADR where the decision lives in the code. // Path shape: ADR-0008. at the point that builds a URL, // Visibility inherits: ADR-0024. at the guard. Twenty-seven decisions are unreachable from code otherwise, and the next maintainer changes something whose reasoning they never saw. verify.sh fails on a citation naming an ADR that does not exist.
• Comment the trap, not the mechanism. NFC normalisation, the settle window, parse order for template overrides, the old ∪ new membership rule — each is a line of code that looks arbitrary and is not. Those are the comments worth writing.

Errors

• Wrap with %w at package boundaries, with operation and path: parse %s: %w.
• Never log and return the same error. Handle it, or return it.
• Request-time render failure degrades: log, serve what exists, never 500 on a missing field. Startup failure is fatal and loud. Content authoring errors name the file and line.

Tests

• Behaviour ships with a test. A change to cmd/ or internal/ carries a _test.go change in the same commit; verify.sh fails otherwise. Test the observable contract, not coverage for its own sake — one test proving the new behaviour is enough, and a refactor with no behaviour change needs only the existing tests to still pass (touch them or say why not).
• Table-driven. Golden files in testdata/, regenerated behind a -update flag.
• Test the observable contract: URL in → bytes out; file on disk → page struct. Do not test private helpers, and do not add a seam solely to make something testable.
• Needing a mock means the design is probably wrong — use a testdata directory with os.DirFS/fstest.MapFS.
• One end-to-end test per route beats ten unit tests of render internals.

Performance

Correct and small first; fast where measured. The render path is the only hot path.

• Write to io.Writer, never build pages by string concatenation.
• Parse templates once at startup; never per request.
• No sync.Pool, caching layer, or goroutines in the render path until a benchmark justifies it and the number goes in the commit message.
• No reflection in the hot path. Extra lookups are map reads, not reflection.
• Benchmarks live next to what they measure, added only when a decision depends on them.

Frontend output

Semantic HTML working with zero JavaScript. Progressive enhancement only. No build step for CSS. Page-specific styles and scripts come from the bundle (styles/scripts frontmatter). Respect prefers-reduced-motion. Every image gets width, height, and alt. Payload discipline is a feature of this project, not an optimisation.

Git

One feature per commit. Imperative subject under 72 characters; body says why. Doc updates ride in the same commit as the code that made them true.