From edb925a91f4fafb9056d181dd620937992ad6c1b Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Thu, 6 Jun 2019 23:21:44 +0300
Subject: [PATCH] syntax: Use `MultiItemModifier` for built-in derives

---
 src/libsyntax/ext/base.rs         |  7 ++----
 src/libsyntax/ext/expand.rs       | 40 +++++++++++++++----------------
 src/libsyntax_ext/deriving/mod.rs | 24 +++++++++++++++----
 3 files changed, 42 insertions(+), 29 deletions(-)

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 9979f5d0a0edf..4a357b0f3121a 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -1,6 +1,6 @@
 pub use SyntaxExtension::*;
 
-use crate::ast::{self, Attribute, Name, PatKind, MetaItem};
+use crate::ast::{self, Attribute, Name, PatKind};
 use crate::attr::HasAttrs;
 use crate::source_map::{SourceMap, Spanned, respan};
 use crate::edition::Edition;
@@ -519,9 +519,6 @@ impl MacResult for DummyResult {
     }
 }
 
-pub type BuiltinDeriveFn =
-    for<'cx> fn(&'cx mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable));
-
 /// Represents different kinds of macro invocations that can be resolved.
 #[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum MacroKind {
@@ -607,7 +604,7 @@ pub enum SyntaxExtension {
                     Vec<Symbol> /* inert attribute names */, Edition),
 
     /// An attribute-like procedural macro that derives a builtin trait.
-    BuiltinDerive(BuiltinDeriveFn),
+    BuiltinDerive(Box<dyn MultiItemModifier + sync::Sync + sync::Send>),
 
     /// A declarative macro, e.g., `macro m() {}`.
     DeclMacro {
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 715303db17378..892c59bbc0446 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -893,29 +893,29 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             edition: ext.edition(self.cx.parse_sess.edition),
         };
 
-        match *ext {
-            ProcMacroDerive(ref ext, ..) => {
-                invoc.expansion_data.mark.set_expn_info(expn_info);
-                let span = span.with_ctxt(self.cx.backtrace());
-                let dummy = ast::MetaItem { // FIXME(jseyfried) avoid this
-                    path: Path::from_ident(Ident::invalid()),
-                    span: DUMMY_SP,
-                    node: ast::MetaItemKind::Word,
+        match ext {
+            ProcMacroDerive(expander, ..) | BuiltinDerive(expander) => {
+                let meta = match ext {
+                    ProcMacroDerive(..) => ast::MetaItem { // FIXME(jseyfried) avoid this
+                        path: Path::from_ident(Ident::invalid()),
+                        span: DUMMY_SP,
+                        node: ast::MetaItemKind::Word,
+                    },
+                    _ => {
+                        expn_info.allow_internal_unstable = Some(vec![
+                            sym::rustc_attrs,
+                            Symbol::intern("derive_clone_copy"),
+                            Symbol::intern("derive_eq"),
+                            // RustcDeserialize and RustcSerialize
+                            Symbol::intern("libstd_sys_internals"),
+                        ].into());
+                        attr.meta()?
+                    }
                 };
-                let items = ext.expand(self.cx, span, &dummy, item);
-                Some(invoc.fragment_kind.expect_from_annotatables(items))
-            }
-            BuiltinDerive(func) => {
-                expn_info.allow_internal_unstable = Some(vec![
-                    sym::rustc_attrs,
-                    Symbol::intern("derive_clone_copy"),
-                    Symbol::intern("derive_eq"),
-                    Symbol::intern("libstd_sys_internals"), // RustcDeserialize and RustcSerialize
-                ].into());
+
                 invoc.expansion_data.mark.set_expn_info(expn_info);
                 let span = span.with_ctxt(self.cx.backtrace());
-                let mut items = Vec::new();
-                func(self.cx, span, &attr.meta()?, &item, &mut |a| items.push(a));
+                let items = expander.expand(self.cx, span, &meta, item);
                 Some(invoc.fragment_kind.expect_from_annotatables(items))
             }
             _ => {
diff --git a/src/libsyntax_ext/deriving/mod.rs b/src/libsyntax_ext/deriving/mod.rs
index ac41f30e6b39f..2f09ab2087e41 100644
--- a/src/libsyntax_ext/deriving/mod.rs
+++ b/src/libsyntax_ext/deriving/mod.rs
@@ -1,8 +1,8 @@
 //! The compiler code necessary to implement the `#[derive]` extensions.
 
 use rustc_data_structures::sync::Lrc;
-use syntax::ast;
-use syntax::ext::base::{Annotatable, ExtCtxt, SyntaxExtension, Resolver};
+use syntax::ast::{self, MetaItem};
+use syntax::ext::base::{Annotatable, ExtCtxt, SyntaxExtension, Resolver, MultiItemModifier};
 use syntax::ext::build::AstBuilder;
 use syntax::ext::hygiene::{Mark, SyntaxContext};
 use syntax::ptr::P;
@@ -39,9 +39,25 @@ pub mod partial_ord;
 #[path="cmp/ord.rs"]
 pub mod ord;
 
-
 pub mod generic;
 
+struct BuiltinDerive(
+    fn(&mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable))
+);
+
+impl MultiItemModifier for BuiltinDerive {
+    fn expand(&self,
+              ecx: &mut ExtCtxt<'_>,
+              span: Span,
+              meta_item: &MetaItem,
+              item: Annotatable)
+              -> Vec<Annotatable> {
+        let mut items = Vec::new();
+        (self.0)(ecx, span, meta_item, &item, &mut |a| items.push(a));
+        items
+    }
+}
+
 macro_rules! derive_traits {
     ($( $name:expr => $func:path, )+) => {
         pub fn is_builtin_trait(name: ast::Name) -> bool {
@@ -55,7 +71,7 @@ macro_rules! derive_traits {
             $(
                 resolver.add_builtin(
                     ast::Ident::with_empty_ctxt(Symbol::intern($name)),
-                    Lrc::new(SyntaxExtension::BuiltinDerive($func))
+                    Lrc::new(SyntaxExtension::BuiltinDerive(Box::new(BuiltinDerive($func))))
                 );
             )*
         }