revtex's abstract belongs after the title, not above it

classprims_test.go

@@ -310,16 +310,22 @@ func pageChars(e *Engine) string {
 			}
 		}
 	}
-	walk(e.mvl)
-	walk(e.parList)
-	// Column-region spans are typeset material too — revtex's frontmatter, a
-	// figure*/table* band — and they reach the page without passing through the main
-	// vertical list.
+	// In PAGE ORDER: a column region's span is typeset material that reaches the page
+	// ABOVE the region's own material — revtex's frontmatter is one, a figure*/table*
+	// band is another — and it never passes through the main vertical list. Walking
+	// the list first and the spans after put a title block AFTER the body it heads.
+	at := 0
 	for _, r := range e.colRegions {
+		if r.at > at {
+			walk(e.mvl[at:r.at])
+			at = r.at
+		}
 		if r.span != nil {
 			walk([]node{r.span})
 		}
 	}
+	walk(e.mvl[at:])
+	walk(e.parList)
 	return string(s)
 }
 

revtex.go

@@ -25,6 +25,15 @@ package engine
 // match against the reference even though every word is present (measured: 2605.12538,
 // 7 authors, went to 5.8 layout-divergence at 94.5% recall). Comma/semicolon joining
 // keeps the block height near revtex's, recovering that layout without losing content.
+// The ABSTRACT is captured, not typeset where it stands. In revtex the abstract is
+// written BEFORE \maketitle and emitted BY it, after the authors; the generic
+// \abstract (latex.go) sets it in place, so the playground and every rendered revtex
+// paper carried its abstract ABOVE its own title. It is collected into a box with
+// \global\setbox — local would be restored by the \endgroup that \end{abstract}
+// runs, and the abstract would vanish — and \maketitle places it. An abstract that
+// comes AFTER \maketitle (some papers do) is emitted as soon as it closes, so the
+// order is right either way and nothing is ever dropped.
+//
 // \author accumulates here — revtex allows several, each followed by its own
 // \affiliation — rather than overwriting as the base article \author does. It runs at
 // document time (from \documentclass), where @ is an "other" character, so it opens
@@ -47,7 +56,14 @@ const RevtexAuthorBlock = `
 \def\preprint#1{}
 \def\pacs#1{}
 \def\keywords#1{}
-\long\def\maketitle{\par\begin{center}{\large\bfseries\@title\par}\medskip{\@revtexauthors\par}\smallskip{\itshape\@revtexaffils\par}\end{center}\par\bigskip\gotex@revtexbodytwocol}
+\newbox\@revtexabsbox
+\newif\if@revtexmadetitle
+\long\def\abstract{\global\setbox\@revtexabsbox\vbox\bgroup
+  \centerline{\small\bfseries Abstract}\smallskip
+  \leftskip=20pt \rightskip=20pt \small}
+\def\endabstract{\egroup\if@revtexmadetitle\@revtexputabstract\fi}
+\def\@revtexputabstract{\par\bigskip\noindent\box\@revtexabsbox\par}
+\long\def\maketitle{\par\begin{center}{\large\bfseries\@title\par}\medskip{\@revtexauthors\par}\smallskip{\itshape\@revtexaffils\par}\end{center}\@revtexputabstract\@revtexmadetitletrue\par\bigskip\gotex@revtexbodytwocol}
 \makeatother
 `
 

revtexabstract_test.go

@@ -0,0 +1,54 @@
+// Copyright (c) the go-tex/engine authors.
+// SPDX-License-Identifier: BSD-3-Clause
+
+package engine
+
+import (
+	"strings"
+	"testing"
+)
+
+// In revtex the abstract is written BEFORE \maketitle and emitted BY it, after the
+// authors. The generic \abstract sets it where it stands, so every rendered revtex
+// paper carried its abstract ABOVE its own title — visible on the deployed
+// playground, and on 2203.15077 whose page 1 opened with "Abstract Growing a flat
+// lamina…" where the reference opens with "How to grow a flat leaf".
+//
+// It costs no page, so Σ cannot see it, which is why it survived.
+func TestRevtexAbstractFollowsTheTitle(t *testing.T) {
+	src := `\documentclass[reprint,aps]{revtex4-2}\begin{document}` +
+		`\title{TITREICI}\author{AUTEURICI}\affiliation{AFFILIATIONICI}` +
+		`\begin{abstract}RESUMEICI\end{abstract}\maketitle CORPSICI\end{document}`
+	e, err := compile([]byte(src), Options{Lenient: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := pageChars(e)
+	order := []string{"TITREICI", "AUTEURICI", "AFFILIATIONICI", "RESUMEICI", "CORPSICI"}
+	at := -1
+	for _, want := range order {
+		i := strings.Index(got, want)
+		if i < 0 {
+			t.Fatalf("%q is not on the page: %q", want, got)
+		}
+		if i < at {
+			t.Errorf("%q comes before what should precede it — order is %v in %q", want, order, got)
+		}
+		at = i
+	}
+}
+
+// An abstract written AFTER \maketitle (some papers do) is emitted as soon as it
+// closes, so nothing is ever captured into a box that no one empties.
+func TestRevtexAbstractAfterMaketitleIsStillSet(t *testing.T) {
+	src := `\documentclass[reprint,aps]{revtex4-2}\begin{document}` +
+		`\title{TITREICI}\author{AUTEURICI}\maketitle` +
+		`\begin{abstract}RESUMEICI\end{abstract} CORPSICI\end{document}`
+	e, err := compile([]byte(src), Options{Lenient: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := pageChars(e); !strings.Contains(got, "RESUMEICI") {
+		t.Errorf("the abstract vanished: %q", got)
+	}
+}

theorem_test.go

@@ -28,16 +28,21 @@ func hasRuleNode(nodes []node) bool {
 // treeText reads back every typeset character in the main vertical list.
 func treeText(e *Engine) string {
 	var b strings.Builder
-	collectChars(e.mvl, &b)
-	// A column region's SPAN is typeset material that reaches the page without ever
-	// being on the main vertical list — revtex's frontmatter is one, a figure*/table*
-	// band is another. Walking mvl alone made a revtex title block look absent when
-	// it was merely somewhere else.
+	// In PAGE ORDER: a column region's SPAN reaches the page ABOVE the region's own
+	// material and never passes through the main vertical list — revtex's frontmatter
+	// is one, a figure*/table* band is another. Walking mvl alone made a revtex title
+	// block look absent; walking it first and the spans after put it after the body.
+	at := 0
 	for _, r := range e.colRegions {
+		if r.at > at {
+			collectChars(e.mvl[at:r.at], &b)
+			at = r.at
+		}
 		if r.span != nil {
 			collectChars([]node{r.span}, &b)
 		}
 	}
+	collectChars(e.mvl[at:], &b)
 	return b.String()
 }