proc_macro: Turn quote into a regular built-in macro

Previously in was implemented using a special hack in the metadata loader

src/libproc_macro/lib.rs

@@ -19,12 +19,15 @@
 
 #![feature(nll)]
 #![feature(staged_api)]
+#![feature(allow_internal_unstable)]
 #![feature(const_fn)]
+#![feature(decl_macro)]
 #![feature(extern_types)]
 #![feature(in_band_lifetimes)]
 #![feature(optin_builtin_traits)]
 #![feature(mem_take)]
 #![feature(non_exhaustive)]
+#![feature(rustc_attrs)]
 #![feature(specialization)]
 
 #![recursion_limit="256"]
@@ -222,11 +225,10 @@ pub mod token_stream {
 ///
 /// Unquoting is done with `$`, and works by taking the single next ident as the unquoted term.
 /// To quote `$` itself, use `$$`.
-///
-/// This is a dummy macro, the actual implementation is in `quote::quote`.`
 #[unstable(feature = "proc_macro_quote", issue = "54722")]
-#[macro_export]
-macro_rules! quote { () => {} }
+#[allow_internal_unstable(proc_macro_def_site)]
+#[cfg_attr(not(bootstrap), rustc_builtin_macro)]
+pub macro quote ($($t:tt)*) { /* compiler built-in */ }
 
 #[unstable(feature = "proc_macro_internals", issue = "27812")]
 #[doc(hidden)]

src/libproc_macro/quote.rs

@@ -57,9 +57,9 @@ macro_rules! quote {
 }
 
 /// Quote a `TokenStream` into a `TokenStream`.
-/// This is the actual `quote!()` proc macro.
+/// This is the actual implementation of the `quote!()` proc macro.
 ///
-/// It is manually loaded in `CStore::load_macro_untracked`.
+/// It is loaded by the compiler in `register_builtin_macros`.
 #[unstable(feature = "proc_macro_quote", issue = "54722")]
 pub fn quote(stream: TokenStream) -> TokenStream {
     if stream.is_empty() {

src/librustc_metadata/cstore_impl.rs

@@ -30,11 +30,9 @@ use syntax::ast;
 use syntax::attr;
 use syntax::source_map;
 use syntax::edition::Edition;
-use syntax::ext::base::{SyntaxExtension, SyntaxExtensionKind};
-use syntax::ext::proc_macro::BangProcMacro;
 use syntax::parse::source_file_to_stream;
 use syntax::parse::parser::emit_unclosed_delims;
-use syntax::symbol::{Symbol, sym};
+use syntax::symbol::Symbol;
 use syntax_pos::{Span, FileName};
 use rustc_data_structures::bit_set::BitSet;
 
@@ -437,14 +435,6 @@ impl cstore::CStore {
         let data = self.get_crate_data(id.krate);
         if data.is_proc_macro_crate() {
             return LoadedMacro::ProcMacro(data.get_proc_macro(id.index, sess).ext);
-        } else if data.name == sym::proc_macro && data.item_name(id.index) == sym::quote {
-            let client = proc_macro::bridge::client::Client::expand1(proc_macro::quote);
-            let kind = SyntaxExtensionKind::Bang(Box::new(BangProcMacro { client }));
-            let ext = SyntaxExtension {
-                allow_internal_unstable: Some([sym::proc_macro_def_site][..].into()),
-                ..SyntaxExtension::default(kind, data.root.edition)
-            };
-            return LoadedMacro::ProcMacro(Lrc::new(ext));
         }
 
         let def = data.get_macro(id.index);

src/libsyntax_ext/lib.rs

@@ -7,13 +7,18 @@
 #![feature(decl_macro)]
 #![feature(mem_take)]
 #![feature(nll)]
+#![feature(proc_macro_internals)]
+#![feature(proc_macro_quote)]
 #![feature(rustc_diagnostic_macros)]
 
+extern crate proc_macro;
+
 use crate::deriving::*;
 
 use syntax::ast::Ident;
 use syntax::edition::Edition;
 use syntax::ext::base::{SyntaxExtension, SyntaxExtensionKind, MacroExpanderFn};
+use syntax::ext::proc_macro::BangProcMacro;
 use syntax::symbol::sym;
 
 mod error_codes;
@@ -100,4 +105,7 @@ pub fn register_builtin_macros(resolver: &mut dyn syntax::ext::base::Resolver, e
         RustcDecodable: decodable::expand_deriving_rustc_decodable,
         RustcEncodable: encodable::expand_deriving_rustc_encodable,
     }
+
+    let client = proc_macro::bridge::client::Client::expand1(proc_macro::quote);
+    register(sym::quote, SyntaxExtensionKind::Bang(Box::new(BangProcMacro { client })));
 }

src/test/ui/auxiliary/cond_plugin.rs

@@ -3,6 +3,7 @@
 
 #![crate_type = "proc-macro"]
 #![feature(proc_macro_hygiene)]
+#![feature(proc_macro_quote)]
 
 extern crate proc_macro;
 

src/test/ui/auxiliary/proc_macro_def.rs

@@ -3,6 +3,7 @@
 
 #![crate_type = "proc-macro"]
 #![feature(proc_macro_hygiene)]
+#![feature(proc_macro_quote)]
 
 extern crate proc_macro;