Function scopes (#1032)

1 files changed, 34 insertions, 0 deletions

diff --git a/macros/src/util.rs b/macros/src/util.rs
index 53a8354e..6b683e5d 100644
--- a/macros/src/util.rs
+++ b/macros/src/util.rs
@@ -18,6 +18,27 @@ macro_rules! bail {
     };
 }
 
+/// For parsing attributes of the form:
+/// #[attr(
+///   statement;
+///   statement;
+///   returned_expression
+/// )]
+pub struct BlockWithReturn {
+    pub prefix: Vec<syn::Stmt>,
+    pub expr: syn::Stmt,
+}
+
+impl Parse for BlockWithReturn {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let mut stmts = syn::Block::parse_within(input)?;
+        let Some(expr) = stmts.pop() else {
+            return Err(input.error("expected at least one expression"));
+        };
+        Ok(Self { prefix: stmts, expr })
+    }
+}
+
 /// Whether an attribute list has a specified attribute.
 pub fn has_attr(attrs: &mut Vec<syn::Attribute>, target: &str) -> bool {
     take_attr(attrs, target).is_some()
@@ -88,3 +109,16 @@ pub fn meta_line<'a>(lines: &mut Vec<&'a str>, key: &str) -> Result<&'a str> {
         None => bail!(callsite, "missing metadata key: {}", key),
     }
 }
+
+/// Creates a block responsible for building a Scope.
+pub fn create_scope_builder(scope_block: Option<&BlockWithReturn>) -> TokenStream {
+    if let Some(BlockWithReturn { prefix, expr }) = scope_block {
+        quote! { {
+            let mut scope = ::typst::eval::Scope::deduplicating();
+            #(#prefix);*
+            #expr
+        } }
+    } else {
+        quote! { ::typst::eval::Scope::new() }
+    }
+}