Merge pull request #1786 from dtolnay/fieldcall

Fix parenthesization of field expressions in function calls

Author: dtolnay

src/expr.rs

@@ -1036,6 +1036,16 @@ impl IdentFragment for Member {
     }
 }
 
+#[cfg(any(feature = "parsing", feature = "printing"))]
+impl Member {
+    pub(crate) fn is_named(&self) -> bool {
+        match self {
+            Member::Named(_) => true,
+            Member::Unnamed(_) => false,
+        }
+    }
+}
+
 ast_struct! {
     /// The index of an unnamed tuple struct field.
     #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
@@ -3021,15 +3031,6 @@ pub(crate) mod parsing {
         Ok(!trailing_dot)
     }
 
-    impl Member {
-        pub(crate) fn is_named(&self) -> bool {
-            match self {
-                Member::Named(_) => true,
-                Member::Unnamed(_) => false,
-            }
-        }
-    }
-
     #[cfg(feature = "full")]
     #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
     impl Parse for PointerMutability {
@@ -3405,22 +3406,17 @@ pub(crate) mod printing {
     fn print_expr_call(e: &ExprCall, tokens: &mut TokenStream, fixup: FixupContext) {
         outer_attrs_to_tokens(&e.attrs, tokens);
 
-        let call_precedence = if let Expr::Field(_) = &*e.func {
-            Precedence::MIN
-        } else {
-            Precedence::Unambiguous
-        };
         let func_fixup = fixup.leftmost_subexpression_with_begin_operator(
             #[cfg(feature = "full")]
             true,
             false,
         );
-        print_subexpression(
-            &e.func,
-            func_fixup.leading_precedence(&e.func) < call_precedence,
-            tokens,
-            func_fixup,
-        );
+        let needs_group = if let Expr::Field(func) = &*e.func {
+            func.member.is_named()
+        } else {
+            func_fixup.leading_precedence(&e.func) < Precedence::Unambiguous
+        };
+        print_subexpression(&e.func, needs_group, tokens, func_fixup);
 
         e.paren_token.surround(tokens, |tokens| {
             e.args.to_tokens(tokens);

tests/test_expr.rs

@@ -703,6 +703,7 @@ fn test_fixup() {
         quote! { (1 < 2) == (3 < 4) },
         quote! { { (let _ = ()) } },
         quote! { (#[attr] thing).field },
+        quote! { (self.f)() },
     ] {
         let original: Expr = syn::parse2(tokens).unwrap();