Reame PlaceholderType -> InferType

xtask/src/ast_src.rs

@@ -117,7 +117,7 @@ pub(crate) const KINDS_SRC: KindsSrc = KindsSrc {
         "ARRAY_TYPE",
         "SLICE_TYPE",
         "REFERENCE_TYPE",
-        "PLACEHOLDER_TYPE",
+        "INFER_TYPE",
         "FN_POINTER_TYPE",
         "FOR_TYPE",
         "IMPL_TRAIT_TYPE",

xtask/src/codegen/rust.ungram

@@ -197,7 +197,7 @@ Type =
 | ArrayType
 | SliceType
 | ReferenceType
-| PlaceholderType
+| InferType
 | FnPointerType
 | ForType
 | ImplTraitType
@@ -206,28 +206,28 @@ Type =
 ParenType =
   '(' Type ')'
 
-TupleType =
-  '(' fields:Type* ')'
-
 NeverType =
   '!'
 
 PathType =
   Path
 
+TupleType =
+  '(' fields:(Type (',' Type)* ','?)? ')'
+
 PointerType =
   '*' ('const' | 'mut') Type
 
+ReferenceType =
+  '&' 'lifetime'? 'mut'? Type
+
 ArrayType =
   '[' Type ';' Expr ']'
 
 SliceType =
   '[' Type ']'
 
-ReferenceType =
-  '&' 'lifetime'? 'mut'? Type
-
-PlaceholderType =
+InferType =
    '_'
 
 FnPointerType =