Remove inline alignment from stack

The current inline alignment is very broken and leads to lots of subtle weirdness. Getting rid of it simplifies the stack's interface a lot. At a later point either:
- inline alignment will be added back in a better way, or
- all nodes will be able to expand or align themselves, meaning that the stack's children take care of their alignment

src/eval/template.rs

@@ -6,7 +6,7 @@ use std::rc::Rc;
 
 use super::Str;
 use crate::diag::StrResult;
-use crate::geom::{Align, Dir, Gen, GenAxis, Length, Linear, Sides, Size};
+use crate::geom::{Align, Dir, GenAxis, Length, Linear, Sides, Size};
 use crate::layout::{
     Decoration, LayoutNode, LayoutTree, PadNode, PageRun, ParChild, ParNode, StackChild,
     StackNode,
@@ -335,8 +335,7 @@ impl Builder {
     /// Push a block node into the active stack, finishing the active paragraph.
     fn block(&mut self, node: impl Into<LayoutNode>) {
         self.parbreak();
-        let aligns = self.style.aligns;
+        self.stack.push(StackChild::Any(node.into(), self.style.aligns.block));
-        self.stack.push(StackChild::Any(node.into(), aligns));
         self.parbreak();
     }
 
@@ -407,7 +406,7 @@ impl PageBuilder {
 }
 
 struct StackBuilder {
-    dirs: Gen<Dir>,
+    dir: Dir,
     children: Vec<StackChild>,
     last: Last<StackChild>,
     par: ParBuilder,
@@ -416,7 +415,7 @@ struct StackBuilder {
 impl StackBuilder {
     fn new(style: &Style) -> Self {
         Self {
-            dirs: Gen::new(style.dir, Dir::TTB),
+            dir: Dir::TTB,
             children: vec![],
             last: Last::None,
             par: ParBuilder::new(style),
@@ -445,17 +444,17 @@ impl StackBuilder {
     }
 
     fn build(self) -> StackNode {
-        let Self { dirs, mut children, par, mut last } = self;
+        let Self { dir, mut children, par, mut last } = self;
         if let Some(par) = par.build() {
             children.extend(last.any());
             children.push(par);
         }
-        StackNode { dirs, children }
+        StackNode { dir, children }
     }
 }
 
 struct ParBuilder {
-    aligns: Gen<Align>,
+    align: Align,
     dir: Dir,
     line_spacing: Length,
     children: Vec<ParChild>,
@@ -465,7 +464,7 @@ struct ParBuilder {
 impl ParBuilder {
     fn new(style: &Style) -> Self {
         Self {
-            aligns: style.aligns,
+            align: style.aligns.block,
             dir: style.dir,
             line_spacing: style.line_spacing(),
             children: vec![],
@@ -508,10 +507,10 @@ impl ParBuilder {
     }
 
     fn build(self) -> Option<StackChild> {
-        let Self { aligns, dir, line_spacing, children, .. } = self;
+        let Self { align, dir, line_spacing, children, .. } = self;
         (!children.is_empty()).then(|| {
             let node = ParNode { dir, line_spacing, children };
-            StackChild::Any(node.into(), aligns)
+            StackChild::Any(node.into(), align)
         })
     }
 }

src/eval/walk.rs

@@ -2,7 +2,7 @@ use std::rc::Rc;
 
 use super::{Eval, EvalContext, Str, Template, Value};
 use crate::diag::TypResult;
-use crate::geom::{Dir, Gen};
+use crate::geom::Align;
 use crate::layout::{ParChild, ParNode, StackChild, StackNode};
 use crate::syntax::*;
 use crate::util::BoolExt;
@@ -117,11 +117,11 @@ fn walk_item(ctx: &mut EvalContext, label: Str, body: Template) {
             )],
         };
         StackNode {
-            dirs: Gen::new(Dir::TTB, style.dir),
+            dir: style.dir,
             children: vec![
-                StackChild::Any(label.into(), Gen::default()),
+                StackChild::Any(label.into(), Align::Start),
                 StackChild::Spacing((style.text.size / 2.0).into()),
-                StackChild::Any(body.to_stack(&style).into(), Gen::default()),
+                StackChild::Any(body.to_stack(&style).into(), Align::Start),
             ],
         }
     });

src/layout/stack.rs

@@ -6,11 +6,8 @@ use super::*;
 #[derive(Debug)]
 #[cfg_attr(feature = "layout-cache", derive(Hash))]
 pub struct StackNode {
-    /// The inline and block directions of this stack.
+    /// The stacking direction.
-    ///
+    pub dir: Dir,
-    /// The children are stacked along the block direction. The inline direction
-    /// is required for aligning the children.
-    pub dirs: Gen<Dir>,
     /// The nodes to be stacked.
     pub children: Vec<StackChild>,
 }
@@ -21,7 +18,7 @@ pub enum StackChild {
     /// Spacing between other nodes.
     Spacing(Linear),
     /// Any child node and how to align it in the stack.
-    Any(LayoutNode, Gen<Align>),
+    Any(LayoutNode, Align),
 }
 
 impl Layout for StackNode {
@@ -72,7 +69,7 @@ struct StackLayouter<'a> {
     overflowing: bool,
     /// Offset, alignment and frame for all children that fit into the current
     /// region. The exact positions are not known yet.
-    frames: Vec<(Length, Gen<Align>, Rc<Frame>)>,
+    frames: Vec<(Length, Align, Rc<Frame>)>,
     /// Finished frames for previous regions.
     finished: Vec<Constrained<Rc<Frame>>>,
 }
@@ -80,7 +77,7 @@ struct StackLayouter<'a> {
 impl<'a> StackLayouter<'a> {
     /// Create a new stack layouter.
     fn new(stack: &'a StackNode, mut regions: Regions) -> Self {
-        let block = stack.dirs.block.axis();
+        let block = stack.dir.axis();
         let full = regions.current;
         let expand = regions.expand;
 
@@ -107,14 +104,14 @@ impl<'a> StackLayouter<'a> {
         for child in &self.stack.children {
             match *child {
                 StackChild::Spacing(amount) => self.space(amount),
-                StackChild::Any(ref node, aligns) => {
+                StackChild::Any(ref node, align) => {
                     let nodes = node.layout(ctx, &self.regions);
                     let len = nodes.len();
                     for (i, frame) in nodes.into_iter().enumerate() {
                         if i + 1 < len {
                             self.constraints.exact = self.full.to_spec().map(Some);
                         }
-                        self.push_frame(frame.item, aligns);
+                        self.push_frame(frame.item, align);
                     }
                 }
             }
@@ -142,11 +139,11 @@ impl<'a> StackLayouter<'a> {
 
     /// Push a frame into the current or next fitting region, finishing regions
     /// if necessary.
-    fn push_frame(&mut self, frame: Rc<Frame>, aligns: Gen<Align>) {
+    fn push_frame(&mut self, frame: Rc<Frame>, align: Align) {
         let size = frame.size.to_gen(self.block);
 
         // Don't allow `Start` after `End` in the same region.
-        if aligns.block < self.ruler {
+        if align < self.ruler {
             self.finish_region();
         }
 
@@ -172,10 +169,10 @@ impl<'a> StackLayouter<'a> {
         let offset = self.used.block;
         self.used.block += size.block;
         self.used.inline.set_max(size.inline);
-        self.ruler = aligns.block;
+        self.ruler = align;
 
         // Remember the frame with offset and alignment.
-        self.frames.push((offset, aligns, frame));
+        self.frames.push((offset, align, frame));
     }
 
     /// Finish the frame for one region.
@@ -211,20 +208,14 @@ impl<'a> StackLayouter<'a> {
         let mut first = true;
 
         // Place all frames.
-        for (offset, aligns, frame) in self.frames.drain(..) {
+        for (offset, align, frame) in self.frames.drain(..) {
             let stack_size = size.to_gen(self.block);
             let child_size = frame.size.to_gen(self.block);
 
-            // Align along the inline axis.
-            let inline = aligns.inline.resolve(
-                self.stack.dirs.inline,
-                Length::zero() .. stack_size.inline - child_size.inline,
-            );
-
             // Align along the block axis.
-            let block = aligns.block.resolve(
+            let block = align.resolve(
-                self.stack.dirs.block,
+                self.stack.dir,
-                if self.stack.dirs.block.is_positive() {
+                if self.stack.dir.is_positive() {
                     offset .. stack_size.block - self.used.block + offset
                 } else {
                     let offset_with_self = offset + child_size.block;
@@ -233,7 +224,7 @@ impl<'a> StackLayouter<'a> {
                 },
             );
 
-            let pos = Gen::new(inline, block).to_point(self.block);
+            let pos = Gen::new(Length::zero(), block).to_point(self.block);
 
             // The baseline of the stack is that of the first frame.
             if first {

src/library/layout.rs

@@ -204,27 +204,11 @@ pub fn stack(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
         Value::Template(v) => Self::Any(v),
     }
 
-    let dir = args.named("dir")?;
+    let dir = args.named("dir")?.unwrap_or(Dir::TTB);
     let spacing = args.named("spacing")?;
     let list: Vec<Child> = args.all().collect();
 
     Ok(Value::Template(Template::from_block(move |style| {
-        let mut dirs = Gen::new(style.dir, dir.unwrap_or(Dir::TTB));
-
-        // If the directions become aligned, fix up the inline direction since
-        // that's the one that is not user-defined.
-        if dirs.inline.axis() == dirs.block.axis() {
-            dirs.inline = Dir::TTB;
-        }
-
-        // Use the current alignments for all children, but take care to apply
-        // them to the correct axes (by swapping them if the stack axes are
-        // different from the style axes).
-        let mut aligns = style.aligns;
-        if dirs.inline.axis() != style.dir.axis() {
-            aligns = Gen::new(aligns.block, aligns.inline);
-        }
-
         let mut children = vec![];
         let mut delayed = None;
 
@@ -241,13 +225,13 @@ pub fn stack(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
                     }
 
                     let node = template.to_stack(style).into();
-                    children.push(StackChild::Any(node, aligns));
+                    children.push(StackChild::Any(node, style.aligns.block));
                     delayed = spacing;
                 }
             }
         }
 
-        StackNode { dirs, children }
+        StackNode { dir, children }
     })))
 }
 

tests/typ/layout/stack.typ

@@ -20,9 +20,6 @@
 #stack(dir: btt, ..items)
 #pagebreak()
 
-// Currently stack works like flexbox apparently.
-#stack(dir: ltr, ..items)
-
 ---
 // Test spacing.
 #page(width: 50pt, margins: 0pt)