Remove guards for built-in elements

The only recursive built-in show rule was the one for equations and that one was unnecessary.

crates/typst/src/foundations/content.rs

@@ -159,11 +159,6 @@ impl Content {
         self.inner.guards.contains(&guard)
     }
 
-    /// Whether no show rule was executed for this content so far.
-    pub fn is_pristine(&self) -> bool {
-        self.inner.guards.is_empty()
-    }
-
     /// Whether this content has already been prepared.
     pub fn is_prepared(&self) -> bool {
         self.inner.prepared

crates/typst/src/foundations/element.rs

@@ -331,9 +331,4 @@ pub enum Behaviour {
 
 /// Guards content against being affected by the same show rule multiple times.
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
-pub enum Guard {
-    /// The nth recipe from the top of the chain.
-    Nth(usize),
-    /// The [base recipe](Show) for a kind of element.
-    Base(Element),
-}
+pub struct Guard(pub usize);

crates/typst/src/math/equation.rs

@@ -3,8 +3,8 @@ use std::num::NonZeroUsize;
 use crate::diag::{bail, SourceResult};
 use crate::engine::Engine;
 use crate::foundations::{
-    elem, Content, Finalize, Guard, NativeElement, Packed, Resolve, Show, Smart,
-    StyleChain, Synthesize,
+    elem, Content, Finalize, NativeElement, Packed, Resolve, Smart, StyleChain,
+    Synthesize,
 };
 use crate::introspection::{Count, Counter, CounterUpdate, Locatable};
 use crate::layout::{
@@ -47,7 +47,6 @@ use crate::World;
 #[elem(
     Locatable,
     Synthesize,
-    Show,
     Finalize,
     LayoutSingle,
     LayoutMath,
@@ -120,17 +119,6 @@ impl Synthesize for Packed<EquationElem> {
     }
 }
 
-impl Show for Packed<EquationElem> {
-    #[typst_macros::time(name = "math.equation", span = self.span())]
-    fn show(&self, _: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
-        let mut realized = self.clone().pack().guarded(Guard::Base(EquationElem::elem()));
-        if self.block(styles) {
-            realized = AlignElem::new(realized).pack().spanned(self.span());
-        }
-        Ok(realized)
-    }
-}
-
 impl Finalize for Packed<EquationElem> {
     fn finalize(&self, realized: Content, style: StyleChain) -> Content {
         let mut realized = realized;

crates/typst/src/realize/mod.rs

@@ -71,11 +71,7 @@ pub fn realize_block<'a>(
 
 /// Whether the target is affected by show rules in the given style chain.
 pub fn applicable(target: &Content, styles: StyleChain) -> bool {
-    if target.needs_preparation() {
-        return true;
-    }
-
-    if target.can::<dyn Show>() && target.is_pristine() {
+    if target.needs_preparation() || target.can::<dyn Show>() {
         return true;
     }
 
@@ -84,7 +80,7 @@ pub fn applicable(target: &Content, styles: StyleChain) -> bool {
 
     // Find out whether any recipe matches and is unguarded.
     for recipe in styles.recipes() {
-        if recipe.applicable(target) && !target.is_guarded(Guard::Nth(n)) {
+        if !target.is_guarded(Guard(n)) && recipe.applicable(target) {
             return true;
         }
         n -= 1;
@@ -136,8 +132,8 @@ pub fn realize(
 
     // Find an applicable show rule recipe.
     for recipe in styles.recipes() {
-        let guard = Guard::Nth(n);
-        if recipe.applicable(target) && !target.is_guarded(guard) {
+        let guard = Guard(n);
+        if !target.is_guarded(guard) && recipe.applicable(target) {
             if let Some(content) = try_apply(engine, target, recipe, guard)? {
                 return Ok(Some(content));
             }
@@ -146,11 +142,8 @@ pub fn realize(
     }
 
     // Apply the built-in show rule if there was no matching recipe.
-    let guard = Guard::Base(target.func());
-    if !target.is_guarded(guard) {
-        if let Some(showable) = target.with::<dyn Show>() {
-            return Ok(Some(showable.show(engine, styles)?));
-        }
+    if let Some(showable) = target.with::<dyn Show>() {
+        return Ok(Some(showable.show(engine, styles)?));
     }
 
     Ok(None)