Add contextual target function

crates/typst-library/src/foundations/mod.rs

@@ -31,6 +31,8 @@ mod selector;
 mod str;
 mod styles;
 mod symbol;
+#[path = "target.rs"]
+mod target_;
 mod ty;
 mod value;
 mod version;
@@ -61,6 +63,7 @@ pub use self::selector::*;
 pub use self::str::*;
 pub use self::styles::*;
 pub use self::symbol::*;
+pub use self::target_::*;
 pub use self::ty::*;
 pub use self::value::*;
 pub use self::version::*;
@@ -79,6 +82,7 @@ use typst_syntax::Spanned;
 use crate::diag::{bail, SourceResult, StrResult};
 use crate::engine::Engine;
 use crate::routines::EvalMode;
+use crate::{Feature, Features};
 
 /// Foundational types and functions.
 ///
@@ -88,7 +92,7 @@ use crate::routines::EvalMode;
 pub static FOUNDATIONS: Category;
 
 /// Hook up all `foundations` definitions.
-pub(super) fn define(global: &mut Scope, inputs: Dict) {
+pub(super) fn define(global: &mut Scope, inputs: Dict, features: &Features) {
     global.category(FOUNDATIONS);
     global.define_type::<bool>();
     global.define_type::<i64>();
@@ -116,6 +120,9 @@ pub(super) fn define(global: &mut Scope, inputs: Dict) {
     global.define_func::<assert>();
     global.define_func::<eval>();
     global.define_func::<style>();
+    if features.is_enabled(Feature::Html) {
+        global.define_func::<target>();
+    }
     global.define_module(calc::module());
     global.define_module(sys::module(inputs));
 }

crates/typst-library/src/foundations/target.rs

@@ -0,0 +1,38 @@
+use comemo::Tracked;
+
+use crate::diag::HintedStrResult;
+use crate::foundations::{elem, func, Cast, Context};
+
+/// The compilation target.
+#[derive(Debug, Default, Copy, Clone, PartialEq, Hash, Cast)]
+pub enum Target {
+    /// The target that is used for paged, fully laid-out content.
+    #[default]
+    Paged,
+    /// The target that is used for HTML export.
+    Html,
+}
+
+impl Target {
+    /// Whether this is the HTML target.
+    pub fn is_html(self) -> bool {
+        self == Self::Html
+    }
+}
+
+/// This element exists solely to host the `target` style chain field.
+/// It is never constructed and not visible to users.
+#[elem]
+pub struct TargetElem {
+    /// The compilation target.
+    pub target: Target,
+}
+
+/// Returns the current compilation target.
+#[func(contextual)]
+pub fn target(
+    /// The callsite context.
+    context: Tracked<Context>,
+) -> HintedStrResult<Target> {
+    Ok(TargetElem::target_in(context.styles()?))
+}

crates/typst-library/src/lib.rs

@@ -193,7 +193,7 @@ impl LibraryBuilder {
     pub fn build(self) -> Library {
         let math = math::module();
         let inputs = self.inputs.unwrap_or_default();
-        let global = global(math.clone(), inputs);
+        let global = global(math.clone(), inputs, &self.features);
         let std = Value::Module(global.clone());
         Library {
             global,
@@ -236,9 +236,9 @@ pub enum Feature {
 }
 
 /// Construct the module with global definitions.
-fn global(math: Module, inputs: Dict) -> Module {
+fn global(math: Module, inputs: Dict, features: &Features) -> Module {
     let mut global = Scope::deduplicating();
-    self::foundations::define(&mut global, inputs);
+    self::foundations::define(&mut global, inputs, features);
     self::model::define(&mut global);
     self::text::define(&mut global);
     global.reset_category();