Add `std` module for names in the standard library (#4038)

2 files changed, 27 insertions, 5 deletions

diff --git a/crates/typst/src/foundations/scope.rs b/crates/typst/src/foundations/scope.rs
index caa82e13..870fa5b0 100644
--- a/crates/typst/src/foundations/scope.rs
+++ b/crates/typst/src/foundations/scope.rs
@@ -48,8 +48,14 @@ impl<'a> Scopes<'a> {
     pub fn get(&self, var: &str) -> HintedStrResult<&Value> {
         std::iter::once(&self.top)
             .chain(self.scopes.iter().rev())
-            .chain(self.base.map(|base| base.global.scope()))
             .find_map(|scope| scope.get(var))
+            .or_else(|| {
+                self.base.and_then(|base| match base.global.scope().get(var) {
+                    Some(value) => Some(value),
+                    None if var == "std" => Some(&base.std),
+                    None => None,
+                })
+            })
             .ok_or_else(|| unknown_variable(var))
     }
 
@@ -57,8 +63,14 @@ impl<'a> Scopes<'a> {
     pub fn get_in_math(&self, var: &str) -> HintedStrResult<&Value> {
         std::iter::once(&self.top)
             .chain(self.scopes.iter().rev())
-            .chain(self.base.map(|base| base.math.scope()))
             .find_map(|scope| scope.get(var))
+            .or_else(|| {
+                self.base.and_then(|base| match base.math.scope().get(var) {
+                    Some(value) => Some(value),
+                    None if var == "std" => Some(&base.std),
+                    None => None,
+                })
+            })
             .ok_or_else(|| unknown_variable(var))
     }
 
@@ -69,13 +81,19 @@ impl<'a> Scopes<'a> {
             .find_map(|scope| scope.get_mut(var))
             .ok_or_else(|| {
                 match self.base.and_then(|base| base.global.scope().get(var)) {
-                    Some(_) => eco_format!("cannot mutate a constant: {}", var).into(),
+                    Some(_) => cannot_mutate_constant(var),
+                    _ if var == "std" => cannot_mutate_constant(var),
                     _ => unknown_variable(var),
                 }
             })?
     }
 }
 
+#[cold]
+fn cannot_mutate_constant(var: &str) -> HintedString {
+    eco_format!("cannot mutate a constant: {}", var).into()
+}
+
 /// The error message when a variable is not found.
 #[cold]
 fn unknown_variable(var: &str) -> HintedString {
diff --git a/crates/typst/src/lib.rs b/crates/typst/src/lib.rs
index 35915e2b..f41fb605 100644
--- a/crates/typst/src/lib.rs
+++ b/crates/typst/src/lib.rs
@@ -67,7 +67,7 @@ use crate::diag::{warning, FileResult, SourceDiagnostic, SourceResult};
 use crate::engine::{Engine, Route};
 use crate::eval::Tracer;
 use crate::foundations::{
-    Array, Bytes, Content, Datetime, Dict, Module, Scope, StyleChain, Styles,
+    Array, Bytes, Content, Datetime, Dict, Module, Scope, StyleChain, Styles, Value,
 };
 use crate::introspection::{Introspector, Locator};
 use crate::layout::{Alignment, Dir, LayoutRoot};
@@ -297,6 +297,9 @@ pub struct Library {
     /// The default style properties (for page size, font selection, and
     /// everything else configurable via set and show rules).
     pub styles: Styles,
+    /// The standard library as a value.
+    /// Used to provide the `std` variable.
+    pub std: Value,
 }
 
 impl Library {
@@ -333,7 +336,8 @@ impl LibraryBuilder {
         let math = math::module();
         let inputs = self.inputs.unwrap_or_default();
         let global = global(math.clone(), inputs);
-        Library { global, math, styles: Styles::new() }
+        let std = Value::Module(global.clone());
+        Library { global, math, styles: Styles::new(), std }
     }
 }