No allocation for empty Punctuated

dtolnay · Mar 17, 2023 · 0833223 · 0833223
1 parent 0844a62
commit 0833223
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Showing 3 changed files with 204 additions and 95 deletions.
diff --git a/src/expr.rs b/src/expr.rs
@@ -673,6 +673,16 @@ ast_struct! {
 }
 
 impl Expr {
+    #[cfg(feature = "parsing")]
+    const DUMMY: Self = Expr::Path(ExprPath {
+        attrs: Vec::new(),
+        qself: None,
+        path: Path {
+            leading_colon: None,
+            segments: Punctuated::new(),
+        },
+    });
+
     #[cfg(all(feature = "parsing", feature = "full"))]
     pub(crate) fn replace_attrs(&mut self, new: Vec<Attribute>) -> Vec<Attribute> {
         match self {
@@ -2700,26 +2710,15 @@ pub(crate) mod parsing {
         if trailing_dot {
             float_repr.truncate(float_repr.len() - 1);
         }
-        let mut dummy = Expr::Path(ExprPath {
-            attrs: Vec::new(),
-            qself: None,
-            path: Path {
-                leading_colon: None,
-                segments: Punctuated::new(),
-            },
-        });
         for part in float_repr.split('.') {
             let index = crate::parse_str(part).map_err(|err| Error::new(float.span(), err))?;
-            let base = mem::replace(e, dummy);
-            dummy = mem::replace(
-                e,
-                Expr::Field(ExprField {
-                    attrs: Vec::new(),
-                    base: Box::new(base),
-                    dot_token: Token![.](dot_token.span),
-                    member: Member::Unnamed(index),
-                }),
-            );
+            let base = mem::replace(e, Expr::DUMMY);
+            *e = Expr::Field(ExprField {
+                attrs: Vec::new(),
+                base: Box::new(base),
+                dot_token: Token![.](dot_token.span),
+                member: Member::Unnamed(index),
+            });
             *dot_token = Token![.](float.span());
         }
         Ok(!trailing_dot)