chunkmd: a reading list with nothing marking it is citation material

Block, N. 1981. Psychologism and behaviorism. Philosophical Review 90:5-43.
    Dennett, D. C. 1987. The Intentional Stance. MIT Press.
    Geach, P. 1957. Mental Acts. Routledge and Kegan Paul.

That is how a reader or a companion sets the further-reading list at the end
of each chapter: indented under the last paragraph of the essay, with no
heading over it and no numbers beside it. Nothing announced it as a
bibliography, so the chunk stayed body text with no flag, the citation stage
never selected it, and a book made of such chapters came out with one or two
citations. *The Cambridge Companion to Ancient Greek Political Thought* had
three; Chalmers's *Philosophy of Mind* reader had one.

The hard part is that an index line opens identically — `Newton, Isaac, 5,
93, 141` — and a page of them would otherwise flood the table. What tells
them apart is that a reference names a work: five words of three letters or
more on the entry's own line, and not two page numbers written as links.

Over 15,925 unflagged body chunks sampled from the corpus this fires on 2.6%,
and seven of eight sampled were real reference lists.

Recorded in parity/KNOWN.md, and the harness allows this one difference by
name: a chunk the Rust flags and the Python does not, identical in every
other field. A flag the Python sets and the Rust does not is still a failure.

parity/KNOWN.md

@@ -369,3 +369,32 @@ deliberate difference from the Python, not because anything caught it.
 
 `citefind` strips the same marker when it cuts a page of notes into notes.
 
+---
+
+## chunkmd — a reading list with nothing marking it is citation material
+
+`looks_like_citations` flags a chunk carrying a run of reference entries that
+nothing announces — no heading over them, no numbers beside them:
+
+        Block, N. 1981. Psychologism and behaviorism. Philosophical Review 90:5-43.
+        Dennett, D. C. 1987. The Intentional Stance. MIT Press.
+        Geach, P. 1957. Mental Acts. Routledge and Kegan Paul.
+
+That is how a reader or a companion sets the further-reading list at the end
+of each chapter, indented under the last paragraph of the essay. The Python
+this was ported from looked only for note markers, so those chunks stayed
+`role='body'` with no flag, the citation stage never selected them, and books
+made entirely of such chapters came out with one or two citations.
+
+The shape is also an index line — `Newton, Isaac, 5, 93, 141` opens
+identically. What tells them apart is that a reference names a work: five
+words of three letters or more on the entry's own line, and not two page
+numbers written as links.
+
+Over 15,925 unflagged body chunks sampled from the corpus this fires on 2.6%,
+and seven of eight sampled were real reference lists.
+
+The parity harness allows this one difference by name: a chunk the Rust
+flags and the Python does not, identical in every other field. A flag the
+Python sets and the Rust does not is still a failure.
+

parity/tests/chunkmd.rs

@@ -21,9 +21,43 @@ fn rust_records(markdown: &str, budgets: &chunkmd::Budgets) -> Vec<Value> {
         .collect()
 }
 
+/// Whether the only difference is a footnote flag the Rust sets and the
+/// Python does not.
+///
+/// `looks_like_citations` learnt to recognise a run of reference entries
+/// with nothing marking them — no numbers, no heading — which is how a
+/// reader or a companion sets its end-of-chapter reading list. The Python it
+/// was ported from never did, so it left those chunks unflagged and the
+/// citation stage never selected them. Recorded in KNOWN.md; additive only,
+/// so a flag the Python sets and the Rust does not is still a failure.
+fn only_gains_the_footnote_flag(ours: &Value, theirs: &Value) -> bool {
+    let flags = |v: &Value| -> Vec<String> {
+        v.get("flags")
+            .and_then(Value::as_array)
+            .map(|a| {
+                a.iter()
+                    .filter_map(|f| f.as_str().map(str::to_string))
+                    .collect()
+            })
+            .unwrap_or_default()
+    };
+    let (mine, yours) = (flags(ours), flags(theirs));
+    if !yours.iter().all(|f| mine.contains(f)) {
+        return false;
+    }
+    let gained: Vec<&String> = mine.iter().filter(|f| !yours.contains(f)).collect();
+    if gained != [&"footnote_citations".to_string()] {
+        return false;
+    }
+    // Everything else about the chunk has to be identical.
+    ["idx", "page", "chapter", "role", "tokens", "text"]
+        .iter()
+        .all(|field| ours.get(field) == theirs.get(field))
+}
+
 fn compare(case: &str, set: &str, ours: &[Value], theirs: &[Value]) {
     for (at, (ours, theirs)) in ours.iter().zip(theirs).enumerate() {
-        if ours != theirs {
+        if ours != theirs && !only_gains_the_footnote_flag(ours, theirs) {
             let fields = ["idx", "page", "chapter", "role", "tokens", "flags", "text"];
             let differing: Vec<String> = fields
                 .iter()