1 files changed, 76 insertions, 0 deletions
diff --git a/crates/typst-eval/src/rules.rs b/crates/typst-eval/src/rules.rs
new file mode 100644
index 00000000..646354d4
--- /dev/null
+++ b/crates/typst-eval/src/rules.rs
@@ -0,0 +1,76 @@
+use typst_library::diag::{warning, At, SourceResult};
+use typst_library::foundations::{
+    Element, Fields, Func, Recipe, Selector, ShowableSelector, Styles, Transformation,
+};
+use typst_library::layout::BlockElem;
+use typst_library::model::ParElem;
+use typst_syntax::ast::{self, AstNode};
+
+use crate::{Eval, Vm};
+
+impl Eval for ast::SetRule<'_> {
+    type Output = Styles;
+
+    fn eval(self, vm: &mut Vm) -> SourceResult<Self::Output> {
+        if let Some(condition) = self.condition() {
+            if !condition.eval(vm)?.cast::<bool>().at(condition.span())? {
+                return Ok(Styles::new());
+            }
+        }
+
+        let target = self.target();
+        let target = target
+            .eval(vm)?
+            .cast::<Func>()
+            .and_then(|func| {
+                func.element().ok_or_else(|| {
+                    "only element functions can be used in set rules".into()
+                })
+            })
+            .at(target.span())?;
+        let args = self.args().eval(vm)?.spanned(self.span());
+        Ok(target.set(&mut vm.engine, args)?.spanned(self.span()).liftable())
+    }
+}
+
+impl Eval for ast::ShowRule<'_> {
+    type Output = Recipe;
+
+    fn eval(self, vm: &mut Vm) -> SourceResult<Self::Output> {
+        let selector = self
+            .selector()
+            .map(|sel| sel.eval(vm)?.cast::<ShowableSelector>().at(sel.span()))
+            .transpose()?
+            .map(|selector| selector.0);
+
+        let transform = self.transform();
+        let transform = match transform {
+            ast::Expr::Set(set) => Transformation::Style(set.eval(vm)?),
+            expr => expr.eval(vm)?.cast::<Transformation>().at(transform.span())?,
+        };
+
+        let recipe = Recipe::new(selector, transform, self.span());
+        check_show_par_set_block(vm, &recipe);
+
+        Ok(recipe)
+    }
+}
+
+/// Migration hint for `show par: set block(spacing: ..)`.
+fn check_show_par_set_block(vm: &mut Vm, recipe: &Recipe) {
+    if_chain::if_chain! {
+        if let Some(Selector::Elem(elem, _)) = recipe.selector();
+        if *elem == Element::of::<ParElem>();
+        if let Transformation::Style(styles) = recipe.transform();
+        if styles.has::<BlockElem>(<BlockElem as Fields>::Enum::Above as _) ||
+           styles.has::<BlockElem>(<BlockElem as Fields>::Enum::Below as _);
+        then {
+            vm.engine.sink.warn(warning!(
+                recipe.span(),
+                "`show par: set block(spacing: ..)` has no effect anymore";
+                hint: "write `set par(spacing: ..)` instead";
+                hint: "this is specific to paragraphs as they are not considered blocks anymore"
+            ))
+        }
+    }
+}