Rollup merge of #34213 - josephDunne:trait_item_macros, r=jseyfried

**syntax-[breaking-change]** cc #31645
New `TraitItemKind::Macro` variant

This change adds support for macro expansion inside trait items by adding the new `TraitItemKind::Macro` and associated parsing code.

3 files changed, 66 insertions, 20 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index f2a005573d5..9d467b4095a 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -241,6 +241,11 @@ pub trait MacResult {
         None
     }
 
+    /// Create zero or more trait items.
+    fn make_trait_items(self: Box<Self>) -> Option<SmallVector<ast::TraitItem>> {
+        None
+    }
+
     /// Create a pattern.
     fn make_pat(self: Box<Self>) -> Option<P<ast::Pat>> {
         None
@@ -288,6 +293,7 @@ make_MacEager! {
     pat: P<ast::Pat>,
     items: SmallVector<P<ast::Item>>,
     impl_items: SmallVector<ast::ImplItem>,
+    trait_items: SmallVector<ast::TraitItem>,
     stmts: SmallVector<ast::Stmt>,
     ty: P<ast::Ty>,
 }
@@ -305,6 +311,10 @@ impl MacResult for MacEager {
         self.impl_items
     }
 
+    fn make_trait_items(self: Box<Self>) -> Option<SmallVector<ast::TraitItem>> {
+        self.trait_items
+    }
+
     fn make_stmts(self: Box<Self>) -> Option<SmallVector<ast::Stmt>> {
         match self.stmts.as_ref().map_or(0, |s| s.len()) {
             0 => make_stmts_default!(self),
@@ -413,6 +423,14 @@ impl MacResult for DummyResult {
         }
     }
 
+    fn make_trait_items(self: Box<DummyResult>) -> Option<SmallVector<ast::TraitItem>> {
+        if self.expr_only {
+            None
+        } else {
+            Some(SmallVector::zero())
+        }
+    }
+
     fn make_stmts(self: Box<DummyResult>) -> Option<SmallVector<ast::Stmt>> {
         Some(SmallVector::one(
             codemap::respan(self.span,
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 5beb4937207..126f39bcb0e 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -81,8 +81,11 @@ impl_macro_generable! {
         "statement",  .make_stmts, lift .fold_stmt, lift .visit_stmt, |_span| SmallVector::zero();
     SmallVector<P<ast::Item>>:
         "item",       .make_items, lift .fold_item, lift .visit_item, |_span| SmallVector::zero();
+    SmallVector<ast::TraitItem>:
+        "trait item", .make_trait_items, lift .fold_trait_item, lift .visit_trait_item,
+        |_span| SmallVector::zero();
     SmallVector<ast::ImplItem>:
-        "impl item",  .make_impl_items, lift .fold_impl_item, lift .visit_impl_item,
+        "impl item",  .make_impl_items,  lift .fold_impl_item,  lift .visit_impl_item,
         |_span| SmallVector::zero();
 }
 
@@ -754,25 +757,10 @@ fn expand_multi_modified(a: Annotatable, fld: &mut MacroExpander) -> SmallVector
             _ => noop_fold_item(it, fld),
         }.into_iter().map(|i| Annotatable::Item(i)).collect(),
 
-        Annotatable::TraitItem(it) => match it.node {
-            ast::TraitItemKind::Method(_, Some(_)) => {
-                let ti = it.unwrap();
-                SmallVector::one(ast::TraitItem {
-                    id: ti.id,
-                    ident: ti.ident,
-                    attrs: ti.attrs,
-                    node: match ti.node  {
-                        ast::TraitItemKind::Method(sig, Some(body)) => {
-                            let (sig, body) = expand_and_rename_method(sig, body, fld);
-                            ast::TraitItemKind::Method(sig, Some(body))
-                        }
-                        _ => unreachable!()
-                    },
-                    span: ti.span,
-                })
-            }
-            _ => fold::noop_fold_trait_item(it.unwrap(), fld)
-        }.into_iter().map(|ti| Annotatable::TraitItem(P(ti))).collect(),
+        Annotatable::TraitItem(it) => {
+            expand_trait_item(it.unwrap(), fld).into_iter().
+                map(|it| Annotatable::TraitItem(P(it))).collect()
+        }
 
         Annotatable::ImplItem(ii) => {
             expand_impl_item(ii.unwrap(), fld).into_iter().
@@ -900,6 +888,31 @@ fn expand_impl_item(ii: ast::ImplItem, fld: &mut MacroExpander)
     }
 }
 
+fn expand_trait_item(ti: ast::TraitItem, fld: &mut MacroExpander)
+                     -> SmallVector<ast::TraitItem> {
+    match ti.node {
+        ast::TraitItemKind::Method(_, Some(_)) => {
+            SmallVector::one(ast::TraitItem {
+                id: ti.id,
+                ident: ti.ident,
+                attrs: ti.attrs,
+                node: match ti.node  {
+                    ast::TraitItemKind::Method(sig, Some(body)) => {
+                        let (sig, body) = expand_and_rename_method(sig, body, fld);
+                        ast::TraitItemKind::Method(sig, Some(body))
+                    }
+                    _ => unreachable!()
+                },
+                span: ti.span,
+            })
+        }
+        ast::TraitItemKind::Macro(mac) => {
+            expand_mac_invoc(mac, None, ti.attrs, ti.span, fld)
+        }
+        _ => fold::noop_fold_trait_item(ti, fld)
+    }
+}
+
 /// Given a fn_decl and a block and a MacroExpander, expand the fn_decl, then use the
 /// PatIdents in its arguments to perform renaming in the FnDecl and
 /// the block, returning both the new FnDecl and the new Block.
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index bbe989b0f40..fe98394c3e4 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -100,6 +100,21 @@ impl<'a> MacResult for ParserAnyMacro<'a> {
         Some(ret)
     }
 
+    fn make_trait_items(self: Box<ParserAnyMacro<'a>>)
+                       -> Option<SmallVector<ast::TraitItem>> {
+        let mut ret = SmallVector::zero();
+        loop {
+            let mut parser = self.parser.borrow_mut();
+            match parser.token {
+                token::Eof => break,
+                _ => ret.push(panictry!(parser.parse_trait_item()))
+            }
+        }
+        self.ensure_complete_parse(false, "item");
+        Some(ret)
+    }
+
+
     fn make_stmts(self: Box<ParserAnyMacro<'a>>)
                  -> Option<SmallVector<ast::Stmt>> {
         let mut ret = SmallVector::zero();