Auto merge of #27296 - jroesch:type-macros, r=huonw

This pull request implements the functionality for [RFC 873](https://github.com/rust-lang/rfcs/blob/master/text/0873-type-macros.md). This is currently just an update of @freebroccolo's branch from January, the corresponding commits are linked in each commit message.

@nikomatsakis and I had talked about updating the macro language to support a lifetime fragment specifier, and it is possible to do that work on this branch as well. If so we can (collectively) talk about it next week during the pre-RustCamp work week.

3 files changed, 73 insertions, 0 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index b2cff3ed53c..d4b5e67eeb4 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -290,6 +290,10 @@ pub trait MacResult {
     fn make_stmts(self: Box<Self>) -> Option<SmallVector<P<ast::Stmt>>> {
         make_stmts_default!(self)
     }
+
+    fn make_ty(self: Box<Self>) -> Option<P<ast::Ty>> {
+        None
+    }
 }
 
 macro_rules! make_MacEager {
@@ -322,6 +326,7 @@ make_MacEager! {
     items: SmallVector<P<ast::Item>>,
     impl_items: SmallVector<P<ast::ImplItem>>,
     stmts: SmallVector<P<ast::Stmt>>,
+    ty: P<ast::Ty>,
 }
 
 impl MacResult for MacEager {
@@ -359,6 +364,10 @@ impl MacResult for MacEager {
         }
         None
     }
+
+    fn make_ty(self: Box<Self>) -> Option<P<ast::Ty>> {
+        self.ty
+    }
 }
 
 /// Fill-in macro expansion result, to allow compilation to continue
@@ -405,15 +414,24 @@ impl DummyResult {
         }
     }
 
+    pub fn raw_ty(sp: Span) -> P<ast::Ty> {
+        P(ast::Ty {
+            id: ast::DUMMY_NODE_ID,
+            node: ast::TyInfer,
+            span: sp
+        })
+    }
 }
 
 impl MacResult for DummyResult {
     fn make_expr(self: Box<DummyResult>) -> Option<P<ast::Expr>> {
         Some(DummyResult::raw_expr(self.span))
     }
+
     fn make_pat(self: Box<DummyResult>) -> Option<P<ast::Pat>> {
         Some(P(DummyResult::raw_pat(self.span)))
     }
+
     fn make_items(self: Box<DummyResult>) -> Option<SmallVector<P<ast::Item>>> {
         // this code needs a comment... why not always just return the Some() ?
         if self.expr_only {
@@ -422,6 +440,7 @@ impl MacResult for DummyResult {
             Some(SmallVector::zero())
         }
     }
+
     fn make_impl_items(self: Box<DummyResult>) -> Option<SmallVector<P<ast::ImplItem>>> {
         if self.expr_only {
             None
@@ -429,6 +448,7 @@ impl MacResult for DummyResult {
             Some(SmallVector::zero())
         }
     }
+
     fn make_stmts(self: Box<DummyResult>) -> Option<SmallVector<P<ast::Stmt>>> {
         Some(SmallVector::one(P(
             codemap::respan(self.span,
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 66b3768a476..cd60ee0691c 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -1542,6 +1542,45 @@ fn expand_and_rename_method(sig: ast::MethodSig, body: P<ast::Block>,
     }, rewritten_body)
 }
 
+pub fn expand_type(t: P<ast::Ty>, fld: &mut MacroExpander) -> P<ast::Ty> {
+    let t = match t.node.clone() {
+        ast::Ty_::TyMac(mac) => {
+            if fld.cx.ecfg.features.unwrap().type_macros {
+                let expanded_ty = match expand_mac_invoc(mac, t.span,
+                                                         |r| r.make_ty(),
+                                                         mark_ty,
+                                                         fld) {
+                    Some(ty) => ty,
+                    None => {
+                        return DummyResult::raw_ty(t.span);
+                    }
+                };
+
+                // Keep going, outside-in.
+                let fully_expanded = fld.fold_ty(expanded_ty);
+                fld.cx.bt_pop();
+
+                fully_expanded.map(|t| ast::Ty {
+                    id: ast::DUMMY_NODE_ID,
+                    node: t.node,
+                    span: t.span,
+                    })
+            } else {
+                feature_gate::emit_feature_err(
+                    &fld.cx.parse_sess.span_diagnostic,
+                    "type_macros",
+                    t.span,
+                    "type macros are experimental (see issue: #27336)");
+
+                DummyResult::raw_ty(t.span)
+            }
+        }
+        _ => t
+    };
+
+    fold::noop_fold_ty(t, fld)
+}
+
 /// A tree-folder that performs macro expansion
 pub struct MacroExpander<'a, 'b:'a> {
     pub cx: &'a mut ExtCtxt<'b>,
@@ -1592,6 +1631,10 @@ impl<'a, 'b> Folder for MacroExpander<'a, 'b> {
             .into_iter().map(|i| i.expect_impl_item()).collect()
     }
 
+    fn fold_ty(&mut self, ty: P<ast::Ty>) -> P<ast::Ty> {
+        expand_type(ty, self)
+    }
+
     fn new_span(&mut self, span: Span) -> Span {
         new_span(self.cx, span)
     }
@@ -1744,6 +1787,10 @@ fn mark_impl_item(ii: P<ast::ImplItem>, m: Mrk) -> P<ast::ImplItem> {
         .expect_one("marking an impl item didn't return exactly one impl item")
 }
 
+fn mark_ty(ty: P<ast::Ty>, m: Mrk) -> P<ast::Ty> {
+    Marker { mark: m }.fold_ty(ty)
+}
+
 /// Check that there are no macro invocations left in the AST:
 pub fn check_for_macros(sess: &parse::ParseSess, krate: &ast::Crate) {
     visit::walk_crate(&mut MacroExterminator{sess:sess}, krate);
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index adc88c329a3..d16fde7bc39 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -117,6 +117,12 @@ impl<'a> MacResult for ParserAnyMacro<'a> {
         self.ensure_complete_parse(false);
         Some(ret)
     }
+
+    fn make_ty(self: Box<ParserAnyMacro<'a>>) -> Option<P<ast::Ty>> {
+        let ret = self.parser.borrow_mut().parse_ty();
+        self.ensure_complete_parse(true);
+        Some(ret)
+    }
 }
 
 struct MacroRulesMacroExpander {