apycite 0.2.1

Keep the quote next to the code it justifies, and prove it is still in the source

apycite

Keep the quote next to the code it justifies, and prove it is still in the source.

// cite(RFC 9112 § 3.2): "A client MUST send a Host header field (Section 7.2 of [HTTP]) in all HTTP/1.1 request messages."
if host_count == 0 {
    return violation(...);
}

apycite scans your tree for those comments, resolves each source, and writes an apysource citations file. apysource then fetches the real document and checks that the sentence is still in it.

When the spec moves under you, you find out — and you find out where:

  [FAIL] Fragments: snippet verified............. 2/3
         RFC 9112 (https://www.rfc-editor.org/rfc/rfc9112.txt) (1)
           client_host_header: snippet not found in extracted content
             closest match (94% similar, § 3.2)
               source says: A client MUST send a Host header field ... in all HTTP/1.1 request messages.
               not in that passage: response
             cited by src/rules/client_host_header.rs:29

Nothing checks that your implementation matches the sentence — no tool can, and that judgement is reasoning work for humans at review time. Putting the quote next to the branch is what makes the reasoning cheap. apycite's job is the outward half: the quote is real, verbatim, and still in the spec.

Install

pip install apycite       # brings apysource with it

The grammar

<comment> cite(<source>[ § <section>][, <key>: <value>]…): "<quote>"

It is a comment, so it fits everywhere a comment fits — above a branch, inside a const table, next to a match arm, in #[cfg]-gated code. That is the whole reason it is a comment and not a macro.

<source> names an entry in your sources file. It is not a URL. apycite has no idea what an RFC is, what HTML is, or where rfc-editor lives. That sentence was a lie until the pattern that minted rfc-editor links moved out of this package; it is not one now.

<key>: <value> takes any apysource targeting key — the list is read from apysource at import, not copied. A targetter apysource ships tomorrow works in a cite tomorrow, with no release of this package.

label: <name> is apycite's own key, not a targeting one. It names the fragment in the generated store, so a cite can name itself for the sentence it enforces instead of inheriting the path of whichever file happens to sort first. A labelled cite is left out of the (2), (3) numbering, and the same sentence cited in several places can be named from any one of them.

§ <section> is sugar for , section: "§ …", because a codebase citing RFCs writes hundreds of them. One sugar; the general form is right there.

The quote is required. A citation that quotes nothing makes no claim anybody can check.

The quote may run onto the next lines

Normative sentences are long, and a line limit should not have to win against one:

// cite(RFC 9110 § 7.2): "A user agent MUST generate a Host header field in a
// request unless it sends that information as an ":authority" pseudo-header field."
if host_count == 0 {

/* cite(RFC 9112 § 3.2): "A client MUST send a Host header field
 * (Section 7.2 of [HTTP]) in all HTTP/1.1
 * request messages." */

No continuation marker, no trailing backslash. The quote ends on the line that ends with a " — which is the rule one line already obeys, where it reads as "nothing may follow the closing quote". Lines are joined with a single space, and apysource normalises whitespace on both sides of the comparison, so how you wrap a quote is not a fact about it.

Two rules follow, and both stop the run rather than guess:

• A cite may not be swallowed by the quote above it. If a quote is left open, the line below it is not read forward into it — because that line might be another cite, and it would then be gone, from a run that exits 0.

• Quotation marks pair up. RFC 9110 writes "Host" and ":authority", never half of either, so a closed quote has an even number of ". Without that count, breaking a line right after an embedded mark would end the quote early — and the truncated quote is a prefix of the real sentence, so it is genuinely in the source and verifies green while the rest of it goes unchecked. That is the worst thing this tool could do, so it counts.

  The price: a quote containing a lone " — prose about the character itself — cannot be cited. Which mark closes "the " character" was never something to guess between; it is now refused instead.

What is not supported is elision. The quote is contiguous source text, and a trailing ... is the only way to say "and it goes on" (apysource prefix-matches).

It is not a spec tool

Every apysource source class is reachable from a comment, in any language:

// cite(RFC 9110 § 7.2): "A user agent MUST generate a Host header field…"

# cite(Fetch § 3.2): "The `Origin` request header indicates where a fetch originates from."

-- cite(UN Charter, section: Article 51): "Nothing in the present Charter shall impair…"

// cite(MDN Origin, section: Origin header): "The HTTP Origin request header indicates…"

/* cite(CSS Color 4, selector: #resolving-color-values): "…" */

% cite(Some Book, page_start: 40, page_end: 42): "…"

All four of the first ones are in the test suite, checked against the live documents. A tool that only ever ran RFCs would be a lint script wearing a general-purpose hat.

The sources file

An ordinary apysource sources file — the same one apysource check reads. A cite names an entry by its label:

sources:
  - label: RFC 9110
    url: https://www.rfc-editor.org/rfc/rfc9110.txt
    type: text/plain
  - label: Fetch
    url: https://fetch.spec.whatwg.org/
    type: text/html
  - label: MDN Origin                 # MdnRepo claims this URL automatically
    url: https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Origin

Repo claiming, format detection, section trees, anchor inference, redirect surfacing, and turning RFC 9110 into a URL — none of that is apycite's. It is all apysource's, and you reach it by writing a source entry.

Hand-written fragments in that file survive into the output, so the things the grammar deliberately cannot say (a selector-only fragment, a part_of chapter tree) cost you nothing.

RFC NNNN resolves without an entry — not because apycite knows what an RFC is, but because apysource ships the pattern, next to the fetcher that has to know the URL anyway. Another family is a patterns: block in the same sources file, and it is apysource's key, not apycite's:

patterns:
  - match: '^W3C (?P<slug>[a-z0-9-]+)$'
    source: {url: "https://www.w3.org/TR/{slug}/", type: text/html}

An entry beats a pattern, so pinning RFC 9110 to datatracker is one entry.

What apycite writes is the expanded source — full URL, full media type — even when the entry that produced it was a bare - label: RFC 9110. The generated file is evidence, and evidence you have to hold a pattern table beside you to read is not evidence. A reviewer sees the URL that was fetched.

Commands

apycite extract              # scan the tree, write the citations file
apycite extract --frozen     # ...or fail if the committed one is out of date
apycite verify               # check every quote against the source that says it
apycite ratchet              # enforce the migration baseline
apycite styles --path x.zig  # which comment style a file gets, and why

There is no apycite check. That word is apysource check's, and a CI log must never leave a reader wondering which of two tools passed.

A sensible CI split — extract --frozen and ratchet are offline and fast enough for every pull request; verify fetches, so it runs nightly:

- run: apycite extract --frozen        # the committed file is current
- run: apycite ratchet                 # no new rule without a citation
- run: apysource check specs.yaml      # (or: apycite verify, nightly)

Nothing goes unlooked-at

A scanner meets a file whose language it does not know. The obvious thing is to skip it — and that is a silently dropped citation: a cite in a .zig file goes unread, the report says nothing, CI stays green, and the tool has verified nothing and called it a pass.

So apycite does not skip. It rests on a theorem:

Every string that parses as a cite, in every comment style, contains the literal substring cite(.

That is true by construction of the grammar, it is asserted over every style and placement in the test suite, and it licenses the only safe skip in the tool: a file with no cite( anywhere in it provably has no cites, whatever language it is written in. Every other file must be read:

what we found	what happens
a cite	✅ extracted
a cite that does not parse	❌ error — a typo must break CI, never drop a quote
cite-shaped text that is not a citation (a string literal, prose)	❌ error (configurable to warn)
cite-shaped text in a file with no comment style	❌ error — apycite will not call a tree clean that it could not read
a file with no comment style and no cite(	✅ safe skip, by the theorem
a file that will not decode	❌ error — we could not read it, so we will not promise it holds no cites
a binary file	skipped, and counted in the report
an excluded path	skipped, and the glob is printed every run

sum(buckets) == files walked is a test. And extracting zero cites is not a pass — a validator that validated nothing has not passed. Pass --allow-empty if a tree with no cites is genuinely what you meant.

The ratchet

Adopting cites across a codebase with hundreds of rules is a campaign, not a branch. The baseline is a committed list of in-scope files that still carry no cite, and it may only ever shrink:

apycite ratchet --init     # once: list every file still to migrate
apycite ratchet            # CI: fail if a file enters the list, or left it silently
apycite ratchet --write    # after a batch: shrink the list

--write will not add a file. A new rule with no citation is precisely what the baseline exists to catch, and adding it automatically would be the tool helping you not notice. Putting a file into the baseline takes a human edit, where a reviewer will see it.

When the baseline empties, the permanent rule — every file in scope carries at least one cite — is already being enforced, with no new code.

License

ISC.