Listings: custom listings without fields: keep derivable description/image

claude-notes/plans/2026-10-09-listing-description-precedence.md

@@ -449,6 +449,21 @@ The plan1c caution points to real work, which is now part of Phase 4:
   pipeline's profile should be identical for the same input. Add a test
   for that, because it is the invariant that stops future drift.
 
+## Follow-up after #815 (2026-10-09)
+
+#814 (this plan) and #815 (bd-p80b9jy9, `fields:` gating) both merged.
+The template conflict resolved as `$if(show.description)$` around
+`$if(show-description)$`.
+
+- [x] `fields_items_carry` (custom listings without `fields:`) counts a
+      description or image that L7 can derive, like `effective_fields`
+      does. Unit test
+      `custom_listing_without_fields_keeps_derivable_fields`; integration
+      test `listing_derives_description_present_only_in_rendered_output`
+      now also covers `custom.html`. Both fail without the fix.
+- [x] Docs: the Fields section in `listings.qmd` says document items
+      count as having a description and an image.
+
 ## Risks / tradeoffs
 
 - **Pass-1 cost and determinism.** L1 reads mtime per document. That makes

claude-notes/plans/listing-description-precedence-investigation/README.md

@@ -65,3 +65,14 @@ Identical to Q1 except c, where q2's documented `listing-item:` override
 wins. No envelope markers remain in the output, and in the grid the
 derived description keeps its link (`<a href="posts/b.html">BODY-B
 paragraph.</a>`).
+
+## Follow-up after #815 (2026-10-09)
+
+#815 (bd-p80b9jy9) gave `type: custom` without `fields:` the fields some
+item carries (`fields_items_carry`). That check didn't count a
+description or image that only L7 can derive, so a custom listing whose
+items had no L1 description dropped the envelope. `custom.qmd` lists
+`derived-only/e.qmd`, whose only paragraph sits inside a div. L1 skips
+that paragraph, but L7 finds it in the rendered page. Before the fix,
+`INSIDE-DIV-E paragraph.` was missing from `custom.html`; after the fix,
+it shows.

claude-notes/plans/listing-description-precedence-investigation/repro/custom.qmd

@@ -0,0 +1,7 @@
+---
+title: custom listing (no fields:, only a derivable description)
+listing:
+  type: custom
+  template: custom.template
+  contents: derived-only/e.qmd
+---

claude-notes/plans/listing-description-precedence-investigation/repro/custom.template

@@ -0,0 +1,3 @@
+$for(items)$
+$it:item-default()$
+$endfor$

claude-notes/plans/listing-description-precedence-investigation/repro/derived-only/e.qmd

@@ -0,0 +1,7 @@
+---
+title: Post E
+---
+
+::: {.wrapper}
+INSIDE-DIV-E paragraph.
+:::

crates/quarto-core/src/project/listing/binding.rs

@@ -128,7 +128,9 @@ pub(crate) fn effective_fields(listing: &Listing, items: &[ListingItem]) -> Vec<
 }
 
 /// Every field at least one item carries: the curated fields in a
-/// fixed order, then custom (`extra`) keys in first-seen order.
+/// fixed order, then custom (`extra`) keys in first-seen order. A
+/// description or image L7 may still derive counts as carried (Q1:
+/// every document item carries both placeholders).
 fn fields_items_carry(items: &[ListingItem]) -> Vec<String> {
     const CURATED: &[&str] = &[
         "date",
@@ -148,8 +150,12 @@ fn fields_items_carry(items: &[ListingItem]) -> Vec<String> {
         .iter()
         .filter(|f| {
             items.iter().any(|it| match **f {
-                "image" => it.image.is_some(),
+                "image" => it.image.is_some() || derivable(it, it.image_source),
                 // Presence only — the date style doesn't matter.
+                "description" => {
+                    item_field_cell(it, "description", &DateStyle::Medium).is_some()
+                        || derivable(it, it.description_source)
+                }
                 f => item_field_cell(it, f, &DateStyle::Medium).is_some(),
             })
         })
@@ -1676,6 +1682,52 @@ mod tests {
         );
     }
 
+    fn field_names(ctx: &TemplateContext) -> Vec<String> {
+        let TemplateValue::List(fields) =
+            ctx.get("listing").unwrap().get_path(&["fields"]).unwrap()
+        else {
+            panic!("fields not a list");
+        };
+        fields
+            .iter()
+            .map(|f| match f {
+                TemplateValue::String(s) => s.clone(),
+                _ => panic!("non-string field"),
+            })
+            .collect()
+    }
+
+    // A custom listing without `fields:` keeps `description` and
+    // `image` when L7 can still derive them, so `$items:item-default()$`
+    // emits their envelopes instead of dropping them.
+    #[test]
+    fn custom_listing_without_fields_keeps_derivable_fields() {
+        let mut l = Listing {
+            kind: ListingType::Custom,
+            ..Listing::default()
+        };
+        super::super::config::apply_type_defaults(&mut l);
+        let mut i = item("X");
+        i.description = None;
+        i.description_source = FieldSource::Absent;
+        i.image = None;
+        i.image_source = FieldSource::Absent;
+        let names = field_names(&ctx_for(&l, &[i.clone()]));
+        for f in ["description", "image"] {
+            assert!(names.contains(&f.to_string()), "missing `{f}` in {names:?}");
+        }
+
+        // A record with no link has nothing to derive from.
+        i.target = crate::project::listing::item::ItemTarget::None;
+        let names = field_names(&ctx_for(&l, &[i]));
+        for f in ["description", "image"] {
+            assert!(
+                !names.contains(&f.to_string()),
+                "unexpected `{f}` in {names:?}"
+            );
+        }
+    }
+
     // `image` is exempt from presence filtering (Q1: placeholders
     // can fill it at render time even when no item declares one).
     #[test]

crates/quarto-core/tests/integration/listing_description_precedence.rs

@@ -212,9 +212,19 @@ fn listing_derives_description_present_only_in_rendered_output() {
         for t in ["default", "grid", "table"] {
             write(&dir.join(format!("{t}.qmd")), &listing_page(t));
         }
+        // A custom listing without `fields:` takes the fields its
+        // items carry; a description only L7 can derive must count.
+        write(
+            &dir.join("custom.qmd"),
+            "---\ntitle: custom\nlisting:\n  type: custom\n  template: custom.template\n  contents: posts\n---\n",
+        );
+        write(
+            &dir.join("custom.template"),
+            "$for(items)$\n$it:item-default()$\n$endfor$\n",
+        );
     });
     render(&dir);
-    for t in ["default", "grid", "table"] {
+    for t in ["default", "grid", "table", "custom"] {
         let page = format!("{t}.html");
         let html = read(&dir.join("_site").join(&page));
         assert_shows(&html, &page, &["RENDERED-ONLY paragraph."], &[]);

docs/guides/projects/listings.qmd

@@ -153,7 +153,9 @@ These cards show only a date, a title and a description. There is no
 image area, and no author, subtitle, reading time or categories, even
 for items that have them. Without `fields:`, a listing uses its type's
 default set and keeps only the fields at least one item has, plus
-`image`.
+`image`. An item that is a project document always counts as having a
+description and an image, since Quarto can derive both from the
+rendered page.
 
 `image` is the exception: when it's in the set, every card gets an image
 area. An item with no image of its own (see