From 0fef85706451331b00d09dc85a77a812c779ce6c Mon Sep 17 00:00:00 2001
From: Laurenz <laurmaedje@gmail.com>
Date: Tue, 12 Mar 2024 12:32:53 +0100
Subject: [PATCH] Fix `Behaviour` of spacing (#3634)

---
 crates/typst/src/introspection/metadata.rs |   2 ++
 crates/typst/src/layout/spacing.rs         |   4 ++--
 crates/typst/src/realize/behaviour.rs      |   6 ++++--
 crates/typst/src/realize/mod.rs            |   3 +++
 tests/ref/bugs/spacing-behaviour.png       | Bin 0 -> 638 bytes
 tests/typ/bugs/spacing-behaviour.typ       |   9 +++++++++
 6 files changed, 20 insertions(+), 4 deletions(-)
 create mode 100644 tests/ref/bugs/spacing-behaviour.png
 create mode 100644 tests/typ/bugs/spacing-behaviour.typ

diff --git a/crates/typst/src/introspection/metadata.rs b/crates/typst/src/introspection/metadata.rs
index 287bef678..2d6d8953f 100644
--- a/crates/typst/src/introspection/metadata.rs
+++ b/crates/typst/src/introspection/metadata.rs
@@ -37,6 +37,8 @@ impl Show for Packed<MetadataElem> {
     }
 }
 
+// TODO: Metadata shows as empty content, so this behaviour is unnecessary. It
+// can be removed once 0.11 has landed.
 impl Behave for Packed<MetadataElem> {
     fn behaviour(&self) -> Behaviour {
         Behaviour::Invisible
diff --git a/crates/typst/src/layout/spacing.rs b/crates/typst/src/layout/spacing.rs
index 7367c1aa1..f3cb765be 100644
--- a/crates/typst/src/layout/spacing.rs
+++ b/crates/typst/src/layout/spacing.rs
@@ -68,7 +68,7 @@ impl Behave for Packed<HElem> {
         } else if self.weak(StyleChain::default()) {
             Behaviour::Weak(1)
         } else {
-            Behaviour::Invisible
+            Behaviour::Ignorant
         }
     }
 
@@ -166,7 +166,7 @@ impl Behave for Packed<VElem> {
         } else if self.weakness(StyleChain::default()) > 0 {
             Behaviour::Weak(self.weakness(StyleChain::default()))
         } else {
-            Behaviour::Invisible
+            Behaviour::Ignorant
         }
     }
 
diff --git a/crates/typst/src/realize/behaviour.rs b/crates/typst/src/realize/behaviour.rs
index 533185552..ae44a23e6 100644
--- a/crates/typst/src/realize/behaviour.rs
+++ b/crates/typst/src/realize/behaviour.rs
@@ -16,9 +16,11 @@ pub enum Behaviour {
     /// An element that destroys adjacent weak elements.
     Destructive,
     /// An element that does not interact at all with other elements, having the
-    /// same effect as if it didn't exist, but has a visual representation.
+    /// same effect as if it didn't exist, but has layout extent and/or a visual
+    /// representation.
     Ignorant,
-    /// An element that does not have a visual representation.
+    /// An element that does not have any layout extent or visual
+    /// representation.
     Invisible,
 }
 
diff --git a/crates/typst/src/realize/mod.rs b/crates/typst/src/realize/mod.rs
index 5409cc253..69a961b06 100644
--- a/crates/typst/src/realize/mod.rs
+++ b/crates/typst/src/realize/mod.rs
@@ -416,6 +416,9 @@ struct ParBuilder<'a>(BehavedBuilder<'a>);
 impl<'a> ParBuilder<'a> {
     fn accept(&mut self, content: &'a Content, styles: StyleChain<'a>) -> bool {
         if content.is::<MetaElem>() {
+            // TODO: This could probably just be `self.0.is_empty()` since no
+            // weak or invisible elements can be at the start of the builder. It
+            // can be removed once 0.11 has landed.
             if self.0.has_strong_elements(false) {
                 self.0.push(content, styles);
                 return true;
diff --git a/tests/ref/bugs/spacing-behaviour.png b/tests/ref/bugs/spacing-behaviour.png
new file mode 100644
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diff --git a/tests/typ/bugs/spacing-behaviour.typ b/tests/typ/bugs/spacing-behaviour.typ
new file mode 100644
index 000000000..a2a30b8ad
--- /dev/null
+++ b/tests/typ/bugs/spacing-behaviour.typ
@@ -0,0 +1,9 @@
+// Test that metadata after spacing does not force a new paragraph.
+
+---
+#{
+  h(1em)
+  counter(heading).update(4)
+  [Hello ]
+  counter(heading).display()
+}