feat(syntex): Squash #[derive_X]#[derive_Y] into #[derive(X,Y)]

This avoids rust-lang/rust#32655.

syntex/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "syntex"
-version = "0.30.0"
+version = "0.30.1"
 authors = [ "erick.tryzelaar@gmail.com" ]
 license = "MIT/Apache-2.0"
 description = "A library that enables compile time syntax extension expansion"

syntex/src/lib.rs

@@ -1,5 +1,7 @@
 extern crate syntex_syntax;
 
+mod squash_derive;
+
 use std::fs::File;
 use std::io::{self, Write};
 use std::path::Path;
@@ -147,6 +149,7 @@ impl Registry {
         let ecx = ExtCtxt::new(&sess, cfg, ecfg, &mut gated_cfgs);
 
         let (krate, _) = expand::expand_crate(ecx, self.macros, self.syntax_exts, krate);
+        let krate = squash_derive::squash_derive(krate);
 
         let krate = self.post_expansion_passes.iter()
             .fold(krate, |krate, f| (f)(krate));

syntex/src/squash_derive.rs

@@ -0,0 +1,219 @@
+/// This crate exposes a simple folder that squashes:
+///
+/// ```rust,ignore
+/// #[derive_Foo]
+/// #[derive_Bar]
+/// struct Baz;
+/// ```
+///
+/// Into:
+///
+/// ```rust,ignore
+/// #[derive(Foo, Bar)]
+/// struct Baz;
+/// ```
+
+use syntex_syntax::ast;
+use syntex_syntax::codemap::{Span, Spanned};
+use syntex_syntax::fold::{self, Folder};
+use syntex_syntax::parse::token;
+use syntex_syntax::ptr::P;
+use syntex_syntax::util::move_map::MoveMap;
+
+/// Squash all the `#[derive_*]` into `#[derive(*)]` together.
+pub fn squash_derive(krate: ast::Crate) -> ast::Crate {
+    SquashDeriveFolder.fold_crate(krate)
+}
+
+struct SquashDeriveFolder;
+
+impl Folder for SquashDeriveFolder {
+    fn fold_item_simple(&mut self, mut item: ast::Item) -> ast::Item {
+        let mut attr_folder = SquashDeriveAttrFolder { derive_attr: None };
+        item.attrs = item.attrs.move_flat_map(|x| attr_folder.fold_attribute(x));
+
+        if let Some(derive_attr) = attr_folder.into_attr() {
+            item.attrs.push(derive_attr);
+        }
+
+        fold::noop_fold_item_simple(item, self)
+    }
+
+    fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
+        fold::noop_fold_mac(mac, self)
+    }
+}
+
+struct SquashDeriveAttrFolder {
+    derive_attr: Option<DeriveAttr>,
+}
+
+impl SquashDeriveAttrFolder {
+    fn into_attr(self) -> Option<ast::Attribute> {
+        match self.derive_attr {
+            Some(derive_attr) => {
+                let meta_item = ast::MetaItemKind::List(
+                    token::intern_and_get_ident("derive"),
+                    derive_attr.meta_items,
+                );
+
+                let meta_item = Spanned {
+                    node: meta_item,
+                    span: derive_attr.span,
+                };
+
+                Some(Spanned {
+                    node: ast::Attribute_ {
+                        id: derive_attr.id,
+                        style: derive_attr.style,
+                        value: P(meta_item),
+                        is_sugared_doc: derive_attr.is_sugared_doc,
+                    },
+                    span: derive_attr.span,
+                })
+            }
+            None => None,
+        }
+    }
+}
+
+struct DeriveAttr {
+    id: ast::AttrId,
+    style: ast::AttrStyle,
+    is_sugared_doc: bool,
+    meta_items: Vec<P<ast::MetaItem>>,
+    span: Span,
+}
+
+impl Folder for SquashDeriveAttrFolder {
+    fn fold_attribute(&mut self,
+                      Spanned {
+                          node: ast::Attribute_ { id, style, value, is_sugared_doc },
+                          span,
+                      }: ast::Attribute) -> Option<ast::Attribute> {
+        match value.node {
+            ast::MetaItemKind::Word(ref name) if name.starts_with("derive_") => {
+                let (_, derive_name) = name.split_at("derive_".len());
+                let derive_name = token::intern_and_get_ident(derive_name);
+
+                let meta_word = P(Spanned {
+                    node: ast::MetaItemKind::Word(derive_name),
+                    span: value.span,
+                });
+
+                match self.derive_attr {
+                    Some(ref mut derive_attr) => {
+                        derive_attr.meta_items.push(meta_word);
+                    }
+                    None => {
+                        self.derive_attr = Some(DeriveAttr {
+                            id: id,
+                            style: style,
+                            is_sugared_doc: is_sugared_doc,
+                            meta_items: vec![meta_word],
+                            span: value.span,
+                        });
+                    }
+                }
+
+                return None;
+            }
+            _ => { }
+        }
+
+        Some(Spanned {
+            node: ast::Attribute_ {
+                id: id,
+                style: style,
+                value: value,
+                is_sugared_doc: is_sugared_doc,
+            },
+            span: span,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use syntex_syntax::ast;
+    use syntex_syntax::codemap::{DUMMY_SP, Spanned};
+    use syntex_syntax::fold::Folder;
+    use syntex_syntax::parse::token;
+    use syntex_syntax::ptr::P;
+
+    fn mk_meta_word(name: &str) -> P<ast::MetaItem> {
+        let name = token::intern_and_get_ident(name);
+
+        P(Spanned {
+            node: ast::MetaItemKind::Word(name),
+            span: DUMMY_SP,
+        })
+    }
+
+    fn mk_meta_list(name: &str,
+                    meta_items: Vec<P<ast::MetaItem>>) -> P<ast::MetaItem> {
+        let name = token::intern_and_get_ident(name);
+
+        P(Spanned {
+            node: ast::MetaItemKind::List(name, meta_items),
+            span: DUMMY_SP,
+        })
+    }
+
+    fn mk_attr(meta_item: P<ast::MetaItem>) -> ast::Attribute {
+        Spanned {
+            node: ast::Attribute_ {
+                id: ast::AttrId(0),
+                style: ast::AttrStyle::Outer,
+                value: meta_item,
+                is_sugared_doc: false,
+            },
+            span: DUMMY_SP,
+        }
+    }
+
+    #[test]
+    fn test_squash() {
+        let variant_data = ast::VariantData::Unit(ast::DUMMY_NODE_ID);
+
+        let generics = ast::Generics {
+            lifetimes: vec![],
+            ty_params: P::empty(),
+            where_clause: ast::WhereClause {
+                id: ast::DUMMY_NODE_ID,
+                predicates: vec![],
+            },
+        };
+
+        let item_kind = ast::ItemKind::Struct(variant_data, generics);
+
+        let item = ast::Item {
+            id: ast::DUMMY_NODE_ID,
+            ident: token::str_to_ident("Foo"),
+            attrs: vec![
+                mk_attr(mk_meta_word("derive_A")),
+                mk_attr(mk_meta_word("derive_B")),
+            ],
+            node: item_kind.clone(),
+            vis: ast::Visibility::Inherited,
+            span: DUMMY_SP,
+        };
+
+        assert_eq!(
+            super::SquashDeriveFolder.fold_item_simple(item.clone()),
+            ast::Item {
+                id: ast::DUMMY_NODE_ID,
+                ident: token::str_to_ident("Foo"),
+                attrs: vec![
+                    mk_attr(mk_meta_list(
+                        "derive",
+                        vec![mk_meta_word("A"), mk_meta_word("B")],
+                    )),
+                ],
+                node: item_kind,
+                vis: ast::Visibility::Inherited,
+                span: DUMMY_SP,
+            }
+        );
+    }
+}