Attempt to try to resolve blocking concerns

compiler/rustc_expand/src/expand.rs

@@ -41,6 +41,7 @@ use std::path::PathBuf;
 use std::rc::Rc;
 use std::{iter, mem};
 
+#[cfg(bootstrap)]
 macro_rules! ast_fragments {
     (
         $($Kind:ident($AstTy:ty) {
@@ -165,6 +166,131 @@ macro_rules! ast_fragments {
     }
 }
 
+#[cfg(not(bootstrap))]
+macro_rules! ast_fragments {
+    (
+        $($Kind:ident($AstTy:ty) {
+            $kind_name:expr;
+            $(one fn $mut_visit_ast:ident; fn $visit_ast:ident;)?
+            $(many fn $flat_map_ast_elt:ident; fn $visit_ast_elt:ident($($args:tt)*);)?
+            fn $make_ast:ident;
+        })*
+    ) => {
+        /// A fragment of AST that can be produced by a single macro expansion.
+        /// Can also serve as an input and intermediate result for macro expansion operations.
+        pub enum AstFragment {
+            OptExpr(Option<P<ast::Expr>>),
+            MethodReceiverExpr(P<ast::Expr>),
+            $($Kind($AstTy),)*
+        }
+
+        /// "Discriminant" of an AST fragment.
+        #[derive(Copy, Clone, PartialEq, Eq)]
+        pub enum AstFragmentKind {
+            OptExpr,
+            MethodReceiverExpr,
+            $($Kind,)*
+        }
+
+        impl AstFragmentKind {
+            pub fn name(self) -> &'static str {
+                match self {
+                    AstFragmentKind::OptExpr => "expression",
+                    AstFragmentKind::MethodReceiverExpr => "expression",
+                    $(AstFragmentKind::$Kind => $kind_name,)*
+                }
+            }
+
+            fn make_from<'a>(self, result: Box<dyn MacResult + 'a>) -> Option<AstFragment> {
+                match self {
+                    AstFragmentKind::OptExpr =>
+                        result.make_expr().map(Some).map(AstFragment::OptExpr),
+                    AstFragmentKind::MethodReceiverExpr =>
+                        result.make_expr().map(AstFragment::MethodReceiverExpr),
+                    $(AstFragmentKind::$Kind => result.$make_ast().map(AstFragment::$Kind),)*
+                }
+            }
+        }
+
+        impl AstFragment {
+            pub fn add_placeholders(&mut self, placeholders: &[NodeId]) {
+                if placeholders.is_empty() {
+                    return;
+                }
+                match self {
+                    $($(AstFragment::$Kind(ast) => ast.extend(placeholders.iter().flat_map(|id| {
+                        ${ignore($flat_map_ast_elt)}
+                        placeholder(AstFragmentKind::$Kind, *id, None).$make_ast()
+                    })),)?)*
+                    _ => panic!("unexpected AST fragment kind")
+                }
+            }
+
+            pub fn make_opt_expr(self) -> Option<P<ast::Expr>> {
+                match self {
+                    AstFragment::OptExpr(expr) => expr,
+                    _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
+                }
+            }
+
+            pub fn make_method_receiver_expr(self) -> P<ast::Expr> {
+                match self {
+                    AstFragment::MethodReceiverExpr(expr) => expr,
+                    _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
+                }
+            }
+
+            $(pub fn $make_ast(self) -> $AstTy {
+                match self {
+                    AstFragment::$Kind(ast) => ast,
+                    _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
+                }
+            })*
+
+            fn make_ast<T: InvocationCollectorNode>(self) -> T::OutputTy {
+                T::fragment_to_output(self)
+            }
+
+            pub fn mut_visit_with<F: MutVisitor>(&mut self, vis: &mut F) {
+                match self {
+                    AstFragment::OptExpr(opt_expr) => {
+                        visit_clobber(opt_expr, |opt_expr| {
+                            if let Some(expr) = opt_expr {
+                                vis.filter_map_expr(expr)
+                            } else {
+                                None
+                            }
+                        });
+                    }
+                    AstFragment::MethodReceiverExpr(expr) => vis.visit_method_receiver_expr(expr),
+                    $($(AstFragment::$Kind(ast) => vis.$mut_visit_ast(ast),)?)*
+                    $($(AstFragment::$Kind(ast) =>
+                        ast.flat_map_in_place(|ast| vis.$flat_map_ast_elt(ast)),)?)*
+                }
+            }
+
+            pub fn visit_with<'a, V: Visitor<'a>>(&'a self, visitor: &mut V) {
+                match self {
+                    AstFragment::OptExpr(Some(expr)) => visitor.visit_expr(expr),
+                    AstFragment::OptExpr(None) => {}
+                    AstFragment::MethodReceiverExpr(expr) => visitor.visit_method_receiver_expr(expr),
+                    $($(AstFragment::$Kind(ast) => visitor.$visit_ast(ast),)?)*
+                    $($(AstFragment::$Kind(ast) => for ast_elt in &ast[..] {
+                        visitor.$visit_ast_elt(ast_elt, $($args)*);
+                    })?)*
+                }
+            }
+        }
+
+        impl<'a> MacResult for crate::mbe::macro_rules::ParserAnyMacro<'a> {
+            $(fn $make_ast(self: Box<crate::mbe::macro_rules::ParserAnyMacro<'a>>)
+                           -> Option<$AstTy> {
+                Some(self.make(AstFragmentKind::$Kind).$make_ast())
+            })*
+        }
+    }
+}
+
 ast_fragments! {
     Expr(P<ast::Expr>) { "expression"; one fn visit_expr; fn visit_expr; fn make_expr; }
     Pat(P<ast::Pat>) { "pattern"; one fn visit_pat; fn visit_pat; fn make_pat; }