fix(emitter): split at CHROME_BODY_SLOT before filling marks (finding #6, 49.8→97.8)

.changeset/emitter-fill-order.md

@@ -0,0 +1,5 @@
+---
+"@contentrain/emitter-astro": patch
+---
+
+Fix silent body drop: the generated layout filled marks before splitting at `CHROME_BODY_SLOT`, so the `@@body@@` inside the marker comment was consumed by the `@@…@@` pattern (leaving `<!---->`) and page content was never spliced in (measured: 49.8 vs 97.8). Generated projects now compose via `composeBody` — split at the marker first, then fill each side. The contract constant is unchanged; this was an implementation-order bug.

packages/emitter-astro/src/emit.test.ts

@@ -4,6 +4,11 @@ import { MIGRATION_CONTRACT_VERSION } from '@contentrain/types'
 import type { EmitInput } from './index'
 import { emitAstroProject, wrapLegacyCss, patternToPagePath, pascalCase } from './index'
 
+// Tiny replicas of the emitted fill helpers — used by the ordering-regression test.
+const REPLICA_SLOT = '<!--@@body@@-->'
+const replicaFill = (h: string, m: Record<string, string>) =>
+  h.replace(/@@([a-z0-9_]+)@@/gi, (_a, k: string) => m[k] ?? '')
+
 const ir: ProjectIR = {
   version: MIGRATION_CONTRACT_VERSION,
   site: { url: 'https://example.com', locales: ['en'] },
@@ -138,7 +143,7 @@ describe('emitAstroProject', () => {
     expect(layout).toContain('set:html')
     expect(layout).not.toContain('<header>')
     expect(layout).not.toContain('<slot />')
-    expect(layout).toContain('split(BODY_SLOT)')
+    expect(layout).toContain('composeBody(')
     expect(layout).toContain(`Astro.slots.render('default')`)
     const chrome = JSON.parse(result.files['src/data/chrome/f-article.json']!)
     // legacy before/after pair composes into a single body with the slot between
@@ -154,6 +159,24 @@ describe('emitAstroProject', () => {
     expect(chrome.body.startsWith('<div class="site">')).toBe(true)
   })
 
+  it('the layout composes via composeBody — never fill-then-split', () => {
+    const layout = result.files['src/layouts/FArticle.astro']!
+    expect(layout).toContain('composeBody(chrome.body, marks, content)')
+    expect(layout).not.toContain('fillMarks(chrome.body')
+    const fill = result.files['src/lib/fill.ts']!
+    // composeBody must split at the marker before any filling
+    expect(fill).toMatch(/composeBody[\s\S]*?\.split\(BODY_SLOT\)[\s\S]*?fillMarks\(part, marks\)/)
+  })
+
+  it('regression: filling before splitting eats the marker and drops the body', () => {
+    const chromeBody = `<article><h1>@@title@@</h1><div class="entry-content">${REPLICA_SLOT}</div></article>`
+    const naive = replicaFill(chromeBody, { title: 'T' }).split(REPLICA_SLOT).join('BODY')
+    expect(naive).not.toContain('BODY') // the bug: marker consumed → content silently dropped
+    expect(naive).toContain('<!---->')
+    const correct = chromeBody.split(REPLICA_SLOT).map((p) => replicaFill(p, { title: 'T' })).join('BODY')
+    expect(correct).toContain('<div class="entry-content">BODY</div>')
+  })
+
   it('a body chunk without the marker gets it appended, with a warning', () => {
     const bad = emitAstroProject({
       ir: {

packages/emitter-astro/src/layouts.ts

@@ -49,7 +49,7 @@ export function familyFiles(family: LayoutFamily, lang: string): FamilyGenResult
   files[`src/layouts/${name}.astro`] = `---
 // Family: ${family.id}${family.name ? ` (${family.name})` : ''} — emitted by @contentrain/emitter-astro
 import chrome from '../data/chrome/${family.id}.json'
-import { fillMarks, BODY_SLOT } from '../lib/fill'
+import { fillMarks, composeBody } from '../lib/fill'
 
 interface Props {
   title?: string
@@ -60,8 +60,9 @@ interface Props {
 const { title = '', marks = {}, body } = Astro.props
 const head = fillMarks(chrome.head, marks)
 const content = body ?? (Astro.slots.has('default') ? await Astro.slots.render('default') : '')
-// Marks fill the CHROME only; content splices in untouched, then ONE injection.
-const html = fillMarks(chrome.body, marks).split(BODY_SLOT).join(content)
+// Split at the marker FIRST, then fill marks per side — filling first would
+// eat the @@body@@ inside the marker and silently drop the content.
+const html = composeBody(chrome.body, marks, content)
 ---
 <!doctype html>
 <html lang=${JSON.stringify(lang)}>

packages/emitter-astro/src/scaffold.ts

@@ -81,6 +81,19 @@ export function fillMarks(html: string, marks: Record<string, unknown>): string
   return html.replace(/@@([a-z0-9_]+)@@/gi, (_all, key: string) => esc(marks[key] ?? ''))
 }
 
+/**
+ * Compose the body chrome with the page content. The split happens BEFORE any
+ * mark filling: fillMarks' @@…@@ pattern would otherwise consume the @@body@@
+ * inside the marker comment, leaving <!----> behind and silently dropping the
+ * content (measured cost on a real page: 49.8 vs 97.8).
+ */
+export function composeBody(chromeBody: string, marks: Record<string, unknown>, content: string): string {
+  return chromeBody
+    .split(BODY_SLOT)
+    .map((part) => fillMarks(part, marks))
+    .join(content)
+}
+
 export interface MarkablePost {
   slug: string
   title: string