Allow unbreakable multi-layouters to expand (#5162)

crates/typst/src/layout/container.rs

@@ -487,7 +487,7 @@ impl Packed<BlockElem> {
         engine: &mut Engine,
         locator: Locator,
         styles: StyleChain,
-        base: Size,
+        region: Region,
     ) -> SourceResult<Frame> {
         // Fetch sizing properties.
         let width = self.width(styles);
@@ -495,7 +495,7 @@ impl Packed<BlockElem> {
         let inset = self.inset(styles).unwrap_or_default();
 
         // Build the pod regions.
-        let pod = unbreakable_pod(&width.into(), &height, &inset, styles, base);
+        let pod = unbreakable_pod(&width.into(), &height, &inset, styles, region.size);
 
         // Layout the body.
         let body = self.body(styles);
@@ -518,6 +518,8 @@ impl Packed<BlockElem> {
             // If we have a child that wants to layout with full region access,
             // we layout it.
             Some(BlockBody::MultiLayouter(callback)) => {
+                let expand = (pod.expand | region.expand) & pod.size.map(Abs::is_finite);
+                let pod = Region { expand, ..pod };
                 callback.call(engine, locator, styles, pod.into())?.into_frame()
             }
         };

crates/typst/src/layout/flow/collect.rs

@@ -173,6 +173,7 @@ impl<'a> Collector<'a, '_, '_> {
     fn block(&mut self, elem: &'a Packed<BlockElem>, styles: StyleChain<'a>) {
         let locator = self.locator.next(&elem.span());
         let align = AlignElem::alignment_in(styles).resolve(styles);
+        let alone = self.children.len() == 1;
         let sticky = elem.sticky(styles);
         let breakable = elem.breakable(styles);
         let fr = match elem.height(styles) {
@@ -193,6 +194,7 @@ impl<'a> Collector<'a, '_, '_> {
             self.output.push(Child::Single(self.boxed(SingleChild {
                 align,
                 sticky,
+                alone,
                 fr,
                 elem,
                 styles,
@@ -200,7 +202,6 @@ impl<'a> Collector<'a, '_, '_> {
                 cell: CachedCell::new(),
             })));
         } else {
-            let alone = self.children.len() == 1;
             self.output.push(Child::Multi(self.boxed(MultiChild {
                 align,
                 sticky,
@@ -318,6 +319,7 @@ pub struct LineChild {
 pub struct SingleChild<'a> {
     pub align: Axes<FixedAlignment>,
     pub sticky: bool,
+    pub alone: bool,
     pub fr: Option<Fr>,
     elem: &'a Packed<BlockElem>,
     styles: StyleChain<'a>,
@@ -327,8 +329,10 @@ pub struct SingleChild<'a> {
 
 impl SingleChild<'_> {
     /// Build the child's frame given the region's base size.
-    pub fn layout(&self, engine: &mut Engine, base: Size) -> SourceResult<Frame> {
-        self.cell.get_or_init(base, |base| {
+    pub fn layout(&self, engine: &mut Engine, region: Region) -> SourceResult<Frame> {
+        self.cell.get_or_init(region, |mut region| {
+            // Vertical expansion is only kept if this block is the only child.
+            region.expand.y &= self.alone;
             layout_single_impl(
                 engine.world,
                 engine.introspector,
@@ -338,7 +342,7 @@ impl SingleChild<'_> {
                 self.elem,
                 self.locator.track(),
                 self.styles,
-                base,
+                region,
             )
         })
     }
@@ -356,7 +360,7 @@ fn layout_single_impl(
     elem: &Packed<BlockElem>,
     locator: Tracked<Locator>,
     styles: StyleChain,
-    base: Size,
+    region: Region,
 ) -> SourceResult<Frame> {
     let link = LocatorLink::new(locator);
     let locator = Locator::link(&link);
@@ -368,7 +372,7 @@ fn layout_single_impl(
         route: Route::extend(route),
     };
 
-    elem.layout_single(&mut engine, locator, styles, base)
+    elem.layout_single(&mut engine, locator, styles, region)
         .map(|frame| frame.post_processed(styles))
 }
 

crates/typst/src/layout/flow/distribute.rs

@@ -226,7 +226,10 @@ impl<'a, 'b> Distributor<'a, 'b, '_, '_, '_> {
         }
 
         // Lay out the block.
-        let frame = single.layout(self.composer.engine, self.regions.base())?;
+        let frame = single.layout(
+            self.composer.engine,
+            Region::new(self.regions.base(), self.regions.expand),
+        )?;
 
         // If the block doesn't fit and a followup region may improve things,
         // finish the region.
@@ -422,8 +425,8 @@ impl<'a, 'b> Distributor<'a, 'b, '_, '_, '_> {
             for item in &self.items {
                 let Item::Fr(v, Some(single)) = item else { continue };
                 let length = v.share(frs, fr_space);
-                let base = Size::new(region.size.x, length);
-                let frame = single.layout(self.composer.engine, base)?;
+                let pod = Region::new(Size::new(region.size.x, length), region.expand);
+                let frame = single.layout(self.composer.engine, pod)?;
                 used.x.set_max(frame.width());
                 fr_frames.push(frame);
             }

tests/suite/layout/pad.typ

@@ -32,3 +32,7 @@ Hi #box(pad(left: 10pt)[A]) there
 --- issue-5044-pad-100-percent ---
 #set page(width: 30pt, height: 30pt)
 #pad(100%, block(width: 1cm, height: 1cm, fill: red))
+
+--- issue-5160-unbreakable-pad ---
+#set block(breakable: false)
+#block(width: 100%, pad(x: 20pt, align(right)[A]))