Remove unnecessary boxing of ASDL product children

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

ast/asdl_rs.py

@@ -89,6 +89,7 @@ class TypeInfo:
         self.has_userdata = None
         self.children = set()
         self.boxed = False
+        self.product = False
 
     def __repr__(self):
         return f"<TypeInfo: {self.name}>"
@@ -145,6 +146,7 @@ class FindUserdataTypesVisitor(asdl.VisitorBase):
             info.has_userdata = True
         if len(product.fields) > 2:
             info.boxed = True
+        info.product = True
         self.add_children(name, product.fields)
 
     def add_children(self, name, fields):
@@ -236,7 +238,7 @@ class StructVisitor(TypeInfoEmitVisitor):
         if fieldtype and fieldtype.has_userdata:
             typ = f"{typ}<U>"
         # don't box if we're doing Vec<T>, but do box if we're doing Vec<Option<Box<T>>>
-        if fieldtype and fieldtype.boxed and (not field.seq or field.opt):
+        if fieldtype and fieldtype.boxed and (not (parent.product or field.seq) or field.opt):
             typ = f"Box<{typ}>"
         if field.opt:
             typ = f"Option<{typ}>"

ast/src/ast_gen.rs

@@ -337,8 +337,8 @@ pub enum Cmpop {
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct Comprehension<U = ()> {
-    pub target: Box<Expr<U>>,
-    pub iter: Box<Expr<U>>,
+    pub target: Expr<U>,
+    pub iter: Expr<U>,
     pub ifs: Vec<Expr<U>>,
     pub is_async: usize,
 }
@@ -375,7 +375,7 @@ pub type Arg<U = ()> = Located<ArgData<U>, U>;
 #[derive(Clone, Debug, PartialEq)]
 pub struct KeywordData<U = ()> {
     pub arg: Option<Ident>,
-    pub value: Box<Expr<U>>,
+    pub value: Expr<U>,
 }
 pub type Keyword<U = ()> = Located<KeywordData<U>, U>;
 
@@ -388,13 +388,13 @@ pub type Alias<U = ()> = Located<AliasData, U>;
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct Withitem<U = ()> {
-    pub context_expr: Box<Expr<U>>,
+    pub context_expr: Expr<U>,
     pub optional_vars: Option<Box<Expr<U>>>,
 }
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct MatchCase<U = ()> {
-    pub pattern: Box<Pattern<U>>,
+    pub pattern: Pattern<U>,
     pub guard: Option<Box<Expr<U>>>,
     pub body: Vec<Stmt<U>>,
 }