From 194d357e03dcee73bfdb32a45175c97f4c3ce422 Mon Sep 17 00:00:00 2001
From: Charles Gleason <charles_gleason@alumni.brown.edu>
Date: Tue, 3 Sep 2019 18:42:58 -0400
Subject: [PATCH] Document `From` trait for `LhsExpr`

---
 src/libsyntax/parse/parser/expr.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/libsyntax/parse/parser/expr.rs b/src/libsyntax/parse/parser/expr.rs
index 5b9f0f1df6718..c38b134154d62 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)
     }