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Diffstat (limited to 'crates/span/src/hygiene.rs')
-rw-r--r--crates/span/src/hygiene.rs1
1 files changed, 1 insertions, 0 deletions
diff --git a/crates/span/src/hygiene.rs b/crates/span/src/hygiene.rs
index 18da689922..4f6d792201 100644
--- a/crates/span/src/hygiene.rs
+++ b/crates/span/src/hygiene.rs
@@ -68,6 +68,7 @@ impl SyntaxContextId {
/// A syntax context describes a hierarchy tracking order of macro definitions.
#[derive(Copy, Clone, Hash, PartialEq, Eq)]
pub struct SyntaxContextData {
+ /// Invariant: Only [`SyntaxContextId::ROOT`] has a [`None`] outer expansion.
pub outer_expn: Option<MacroCallId>,
pub outer_transparency: Transparency,
pub parent: SyntaxContextId,