lowering: don't rely on parser directly.

src/librustc/hir/lowering.rs

@@ -70,8 +70,8 @@ use syntax::print::pprust;
 use syntax::source_map::{respan, ExpnData, ExpnKind, DesugaringKind, Spanned};
 use syntax::symbol::{kw, sym, Symbol};
 use syntax::tokenstream::{TokenStream, TokenTree};
-use syntax::parse;
-use syntax::parse::token::{self, Token};
+use syntax::parse::token::{self, Nonterminal, Token};
+use syntax::parse::ParseSess;
 use syntax::visit::{self, Visitor};
 use syntax_pos::Span;
 
@@ -87,6 +87,8 @@ pub struct LoweringContext<'a> {
 
     resolver: &'a mut dyn Resolver,
 
+    parser: &'static dyn Parser,
+
     /// The items being lowered are collected here.
     items: BTreeMap<hir::HirId, hir::Item>,
 
@@ -181,6 +183,13 @@ pub trait Resolver {
     fn has_derives(&self, node_id: NodeId, derives: SpecialDerives) -> bool;
 }
 
+/// HACK(Centril): there is a cyclic dependency between the parser and lowering
+/// if we don't have this trait. To avoid that dependency so that librustc is
+/// independent of the parser, we use type erasure here.
+pub trait Parser {
+    fn nt_to_tokenstream(&self, nt: &Nonterminal, sess: &ParseSess, span: Span) -> TokenStream;
+}
+
 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
 /// and if so, what meaning it has.
 #[derive(Debug)]
@@ -237,6 +246,7 @@ pub fn lower_crate(
     dep_graph: &DepGraph,
     krate: &Crate,
     resolver: &mut dyn Resolver,
+    parser: &'static dyn Parser,
 ) -> hir::Crate {
     // We're constructing the HIR here; we don't care what we will
     // read, since we haven't even constructed the *input* to
@@ -250,6 +260,7 @@ pub fn lower_crate(
         sess,
         cstore,
         resolver,
+        parser,
         items: BTreeMap::new(),
         trait_items: BTreeMap::new(),
         impl_items: BTreeMap::new(),
@@ -1023,10 +1034,7 @@ impl<'a> LoweringContext<'a> {
     fn lower_token(&mut self, token: Token) -> TokenStream {
         match token.kind {
             token::Interpolated(nt) => {
-                // FIXME(Centril): Consider indirection `(parse_sess.nt_to_tokenstream)(...)`
-                // to hack around the current hack that requires `nt_to_tokenstream` to live
-                // in the parser.
-                let tts = parse::nt_to_tokenstream(&nt, &self.sess.parse_sess, token.span);
+                let tts = self.parser.nt_to_tokenstream(&nt, &self.sess.parse_sess, token.span);
                 self.lower_token_stream(tts)
             }
             _ => TokenTree::Token(token).into(),

src/librustc_interface/passes.rs

@@ -5,7 +5,7 @@ use crate::proc_macro_decls;
 use log::{info, warn, log_enabled};
 use rustc::dep_graph::DepGraph;
 use rustc::hir;
-use rustc::hir::lowering::lower_crate;
+use rustc::hir::lowering::{lower_crate, Parser};
 use rustc::hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc::lint;
 use rustc::middle::{self, reachable, resolve_lifetime, stability};
@@ -38,9 +38,12 @@ use syntax::early_buffered_lints::BufferedEarlyLint;
 use syntax::ext::base::{NamedSyntaxExtension, ExtCtxt};
 use syntax::mut_visit::MutVisitor;
 use syntax::parse::{self, PResult};
+use syntax::parse::token::Nonterminal;
+use syntax::parse::ParseSess;
+use syntax::tokenstream::TokenStream;
 use syntax::util::node_count::NodeCounter;
 use syntax::symbol::Symbol;
-use syntax_pos::FileName;
+use syntax_pos::{FileName, Span};
 use syntax_ext;
 
 use rustc_serialize::json;
@@ -532,6 +535,16 @@ fn configure_and_expand_inner<'a>(
     Ok((krate, resolver))
 }
 
+fn parser() -> &'static dyn Parser {
+    struct Parse;
+    impl Parser for Parse {
+        fn nt_to_tokenstream(&self, nt: &Nonterminal, sess: &ParseSess, span: Span) -> TokenStream {
+            syntax::parse::nt_to_tokenstream(nt, sess, span)
+        }
+    }
+    &Parse
+}
+
 pub fn lower_to_hir(
     sess: &Session,
     cstore: &CStore,
@@ -541,7 +554,7 @@ pub fn lower_to_hir(
 ) -> Result<hir::map::Forest> {
     // Lower AST to HIR.
     let hir_forest = time(sess, "lowering AST -> HIR", || {
-        let hir_crate = lower_crate(sess, cstore, &dep_graph, &krate, resolver);
+        let hir_crate = lower_crate(sess, cstore, &dep_graph, &krate, resolver, parser());
 
         if sess.opts.debugging_opts.hir_stats {
             hir_stats::print_hir_stats(&hir_crate);