Tight lists only attach to preceding paragraphs, not blocks anymore (#4396)

crates/typst/src/layout/spacing.rs

@@ -126,12 +126,13 @@ pub struct VElem {
     #[external]
     pub weak: bool,
 
-    /// The element's weakness level, see also [`Behaviour`].
+    /// The spacing's weakness level, see also [`Behaviour`].
     #[internal]
     #[parse(args.named("weak")?.map(|v: bool| v as usize))]
     pub weakness: usize,
 
-    /// Whether the element collapses if there is a parbreak in front.
+    /// Whether the spacing collapses if not immediately preceded by a
+    /// paragraph.
     #[internal]
     #[parse(Some(false))]
     pub attach: bool,

crates/typst/src/realize/mod.rs

@@ -385,16 +385,15 @@ impl<'a> FlowBuilder<'a> {
         content: &'a Content,
         styles: StyleChain<'a>,
     ) -> bool {
+        let last_was_par = self.1;
+        self.1 = false;
+
         if content.is::<ParbreakElem>() {
-            self.1 = true;
             return true;
         }
 
-        let last_was_parbreak = self.1;
-        self.1 = false;
-
         if let Some(elem) = content.to_packed::<VElem>() {
-            if !elem.attach(styles) || !last_was_parbreak {
+            if !elem.attach(styles) || last_was_par {
                 self.0.push(content, styles);
             }
             return true;
@@ -434,6 +433,7 @@ impl<'a> FlowBuilder<'a> {
             self.0.push(*par_spacing, styles);
             self.0.push(content, styles);
             self.0.push(*par_spacing, styles);
+            self.1 = true;
             return true;
         }
 

tests/suite/model/list.typ

@@ -145,3 +145,23 @@ World
 --- issue-2530-list-item-panic ---
 // List item (pre-emptive)
 #list.item[Hello]
+
+--- issue-1850-list-attach-spacing ---
+// List attachment should only work with paragraphs, not other blocks.
+#set page(width: auto)
+#let part = box.with(stroke: 1pt, inset: 3pt)
+#{
+  part[
+    $ x $
+    - A
+  ]
+  part($ x $ + list[A])
+  part($ x $ + list[ A ])
+  part[
+    $ x $
+
+    - A
+  ]
+  part($ x $ + parbreak() + list[A])
+  part($ x $ + parbreak() + parbreak() + list[A])
+}