Add newtype for IsTuple

Author: clubby789

compiler/rustc_builtin_macros/src/deriving/decodable.rs

@@ -198,7 +198,7 @@ where
     match fields {
         Unnamed(fields, is_tuple) => {
             let path_expr = cx.expr_path(outer_pat_path);
-            if !*is_tuple {
+            if matches!(is_tuple, IsTuple::No) {
                 path_expr
             } else {
                 let fields = fields

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -62,8 +62,8 @@ fn default_struct_substructure(
     let default_call = |span| cx.expr_call_global(span, default_ident.clone(), ThinVec::new());
 
     let expr = match summary {
-        Unnamed(_, false) => cx.expr_ident(trait_span, substr.type_ident),
-        Unnamed(fields, true) => {
+        Unnamed(_, IsTuple::No) => cx.expr_ident(trait_span, substr.type_ident),
+        Unnamed(fields, IsTuple::Yes) => {
             let exprs = fields.iter().map(|sp| default_call(*sp)).collect();
             cx.expr_call_ident(trait_span, substr.type_ident, exprs)
         }

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -286,10 +286,16 @@ pub struct FieldInfo {
     pub other_selflike_exprs: Vec<P<Expr>>,
 }
 
+#[derive(Copy, Clone)]
+pub enum IsTuple {
+    No,
+    Yes,
+}
+
 /// Fields for a static method
 pub enum StaticFields {
     /// Tuple and unit structs/enum variants like this.
-    Unnamed(Vec<Span>, bool /*is tuple*/),
+    Unnamed(Vec<Span>, IsTuple),
     /// Normal structs/struct variants.
     Named(Vec<(Ident, Span)>),
 }
@@ -1439,7 +1445,10 @@ impl<'a> TraitDef<'a> {
             }
         }
 
-        let is_tuple = matches!(struct_def, ast::VariantData::Tuple(..));
+        let is_tuple = match struct_def {
+            ast::VariantData::Tuple(..) => IsTuple::Yes,
+            _ => IsTuple::No,
+        };
         match (just_spans.is_empty(), named_idents.is_empty()) {
             (false, false) => cx
                 .dcx()