Document `From` trait for `LhsExpr`

1 files changed, 7 insertions, 0 deletions

diff --git a/src/libsyntax/parse/parser/expr.rs b/src/libsyntax/parse/parser/expr.rs
index 5b9f0f1df67..c38b134154d 100644
--- a/src/libsyntax/parse/parser/expr.rs
+++ b/src/libsyntax/parse/parser/expr.rs
@@ -66,6 +66,10 @@ pub(super) enum LhsExpr {
 }
 
 impl From<Option<ThinVec<Attribute>>> for LhsExpr {
+    /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
+    /// and `None` into `LhsExpr::NotYetParsed`.
+    ///
+    /// This conversion does not allocate.
     fn from(o: Option<ThinVec<Attribute>>) -> Self {
         if let Some(attrs) = o {
             LhsExpr::AttributesParsed(attrs)
@@ -76,6 +80,9 @@ impl From<Option<ThinVec<Attribute>>> for LhsExpr {
 }
 
 impl From<P<Expr>> for LhsExpr {
+    /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
+    ///
+    /// This conversion does not allocate.
     fn from(expr: P<Expr>) -> Self {
         LhsExpr::AlreadyParsed(expr)
     }