From 54604ccb6b96576c0495db48bd6a450dc69bc90b Mon Sep 17 00:00:00 2001
From: Laurenz <laurmaedje@gmail.com>
Date: Wed, 29 May 2024 16:32:20 +0200
Subject: Fix `Default` impls for AST nodes (#4288)

---
 crates/typst-syntax/src/ast.rs  | 22 ++++++++++++++--------
 crates/typst-syntax/src/node.rs | 28 ++++++++++++++++------------
 2 files changed, 30 insertions(+), 20 deletions(-)

(limited to 'crates/typst-syntax')

diff --git a/crates/typst-syntax/src/ast.rs b/crates/typst-syntax/src/ast.rs
index a434e39a..01e0944d 100644
--- a/crates/typst-syntax/src/ast.rs
+++ b/crates/typst-syntax/src/ast.rs
@@ -24,12 +24,6 @@ pub trait AstNode<'a>: Sized {
     }
 }
 
-/// A static syntax node used as a fallback value. This is returned instead of
-/// panicking when the syntactical structure isn't valid. In a normal
-/// compilation, evaluation isn't attempted on a broken file, but for IDE
-/// functionality, it is.
-static ARBITRARY: SyntaxNode = SyntaxNode::arbitrary();
-
 macro_rules! node {
     ($(#[$attr:meta])* $name:ident) => {
         #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
@@ -56,7 +50,9 @@ macro_rules! node {
         impl Default for $name<'_> {
             #[inline]
             fn default() -> Self {
-                Self(&ARBITRARY)
+                static PLACEHOLDER: SyntaxNode
+                    = SyntaxNode::placeholder(SyntaxKind::$name);
+                Self(&PLACEHOLDER)
             }
         }
     };
@@ -392,7 +388,7 @@ impl Expr<'_> {
 
 impl Default for Expr<'_> {
     fn default() -> Self {
-        Expr::Space(Space::default())
+        Expr::None(None::default())
     }
 }
 
@@ -2135,3 +2131,13 @@ impl<'a> FuncReturn<'a> {
         self.0.cast_last_match()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_expr_default() {
+        assert!(Expr::default().to_untyped().cast::<Expr>().is_some());
+    }
+}
diff --git a/crates/typst-syntax/src/node.rs b/crates/typst-syntax/src/node.rs
index b9efde6e..8e623d51 100644
--- a/crates/typst-syntax/src/node.rs
+++ b/crates/typst-syntax/src/node.rs
@@ -39,6 +39,21 @@ impl SyntaxNode {
         Self(Repr::Error(Arc::new(ErrorNode::new(message, text))))
     }
 
+    /// Create a dummy node of the given kind.
+    ///
+    /// Panics if `kind` is `SyntaxKind::Error`.
+    #[track_caller]
+    pub const fn placeholder(kind: SyntaxKind) -> Self {
+        if matches!(kind, SyntaxKind::Error) {
+            panic!("cannot create error placeholder");
+        }
+        Self(Repr::Leaf(LeafNode {
+            kind,
+            text: EcoString::new(),
+            span: Span::detached(),
+        }))
+    }
+
     /// The type of the node.
     pub fn kind(&self) -> SyntaxKind {
         match &self.0 {
@@ -297,17 +312,6 @@ impl SyntaxNode {
             Repr::Error(node) => node.error.span.number() + 1,
         }
     }
-
-    /// An arbitrary node just for filling a slot in memory.
-    ///
-    /// In contrast to `default()`, this is a const fn.
-    pub(super) const fn arbitrary() -> Self {
-        Self(Repr::Leaf(LeafNode {
-            kind: SyntaxKind::End,
-            text: EcoString::new(),
-            span: Span::detached(),
-        }))
-    }
 }
 
 impl Debug for SyntaxNode {
@@ -322,7 +326,7 @@ impl Debug for SyntaxNode {
 
 impl Default for SyntaxNode {
     fn default() -> Self {
-        Self::arbitrary()
+        Self::leaf(SyntaxKind::End, EcoString::new())
     }
 }
 
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