Split out four new crates (#5302)

1 files changed, 107 insertions, 0 deletions

diff --git a/crates/typst-library/src/layout/layout.rs b/crates/typst-library/src/layout/layout.rs
new file mode 100644
index 00000000..c3d112e1
--- /dev/null
+++ b/crates/typst-library/src/layout/layout.rs
@@ -0,0 +1,107 @@
+use comemo::Track;
+use typst_syntax::Span;
+
+use crate::diag::SourceResult;
+use crate::engine::Engine;
+use crate::foundations::{
+    dict, elem, func, Content, Context, Func, NativeElement, Packed, Show, StyleChain,
+};
+use crate::introspection::Locatable;
+use crate::layout::{BlockElem, Size};
+
+/// Provides access to the current outer container's (or page's, if none)
+/// dimensions (width and height).
+///
+/// Accepts a function that receives a single parameter, which is a dictionary
+/// with keys `width` and `height`, both of type [`length`]. The function is
+/// provided [context], meaning you don't need to use it in combination with the
+/// `context` keyword. This is why [`measure`] can be called in the example
+/// below.
+///
+/// ```example
+/// #let text = lorem(30)
+/// #layout(size => [
+///   #let (height,) = measure(
+///     block(width: size.width, text),
+///   )
+///   This text is #height high with
+///   the current page width: \
+///   #text
+/// ])
+/// ```
+///
+/// Note that the `layout` function forces its contents into a [block]-level
+/// container, so placement relative to the page or pagebreaks are not possible
+/// within it.
+///
+/// If the `layout` call is placed inside a box with a width of `{800pt}` and a
+/// height of `{400pt}`, then the specified function will be given the argument
+/// `{(width: 800pt, height: 400pt)}`. If it is placed directly into the page, it
+/// receives the page's dimensions minus its margins. This is mostly useful in
+/// combination with [measurement]($measure).
+///
+/// You can also use this function to resolve [`ratio`] to fixed lengths. This
+/// might come in handy if you're building your own layout abstractions.
+///
+/// ```example
+/// #layout(size => {
+///   let half = 50% * size.width
+///   [Half a page is #half wide.]
+/// })
+/// ```
+///
+/// Note that the width or height provided by `layout` will be infinite if the
+/// corresponding page dimension is set to `{auto}`.
+#[func]
+pub fn layout(
+    /// The call span of this function.
+    span: Span,
+    /// A function to call with the outer container's size. Its return value is
+    /// displayed in the document.
+    ///
+    /// The container's size is given as a [dictionary] with the keys `width`
+    /// and `height`.
+    ///
+    /// This function is called once for each time the content returned by
+    /// `layout` appears in the document. This makes it possible to generate
+    /// content that depends on the dimensions of its container.
+    func: Func,
+) -> Content {
+    LayoutElem::new(func).pack().spanned(span)
+}
+
+/// Executes a `layout` call.
+#[elem(Locatable, Show)]
+struct LayoutElem {
+    /// The function to call with the outer container's (or page's) size.
+    #[required]
+    func: Func,
+}
+
+impl Show for Packed<LayoutElem> {
+    fn show(&self, _: &mut Engine, _: StyleChain) -> SourceResult<Content> {
+        Ok(BlockElem::multi_layouter(
+            self.clone(),
+            |elem, engine, locator, styles, regions| {
+                // Gets the current region's base size, which will be the size of the
+                // outer container, or of the page if there is no such container.
+                let Size { x, y } = regions.base();
+                let loc = elem.location().unwrap();
+                let context = Context::new(Some(loc), Some(styles));
+                let result = elem
+                    .func()
+                    .call(
+                        engine,
+                        context.track(),
+                        [dict! { "width" => x, "height" => y }],
+                    )?
+                    .display();
+                (engine.routines.layout_fragment)(
+                    engine, &result, locator, styles, regions,
+                )
+            },
+        )
+        .pack()
+        .spanned(self.span()))
+    }
+}