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.

9 files changed, 105 insertions, 2 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index db173d08308..eefd3da9f4a 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -1471,6 +1471,8 @@ pub enum Ty_ {
     /// TyInfer means the type should be inferred instead of it having been
     /// specified. This can appear anywhere in a type.
     TyInfer,
+    // A macro in the type position.
+    TyMac(Mac)
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
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 {
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 4a1b74d89d0..dd6fc7ebd0c 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -172,6 +172,9 @@ const KNOWN_FEATURES: &'static [(&'static str, &'static str, Status)] = &[
 
     // Allows associated type defaults
     ("associated_type_defaults", "1.2.0", Active),
+    // Allows macros to appear in the type position.
+
+    ("type_macros", "1.3.0", Active),
 ];
 // (changing above list without updating src/doc/reference.md makes @cmr sad)
 
@@ -354,6 +357,7 @@ pub struct Features {
     pub const_fn: bool,
     pub static_recursion: bool,
     pub default_type_parameter_fallback: bool,
+    pub type_macros: bool,
 }
 
 impl Features {
@@ -380,6 +384,7 @@ impl Features {
             const_fn: false,
             static_recursion: false,
             default_type_parameter_fallback: false,
+            type_macros: false,
         }
     }
 }
@@ -883,6 +888,7 @@ fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler,
         const_fn: cx.has_feature("const_fn"),
         static_recursion: cx.has_feature("static_recursion"),
         default_type_parameter_fallback: cx.has_feature("default_type_parameter_fallback"),
+        type_macros: cx.has_feature("type_macros"),
     }
 }
 
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index dab6d41df30..72fe9a7711d 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -429,6 +429,9 @@ pub fn noop_fold_ty<T: Folder>(t: P<Ty>, fld: &mut T) -> P<Ty> {
             TyPolyTraitRef(bounds) => {
                 TyPolyTraitRef(bounds.move_map(|b| fld.fold_ty_param_bound(b)))
             }
+            TyMac(mac) => {
+                TyMac(fld.fold_mac(mac))
+            }
         },
         span: fld.new_span(span)
     })
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index e7ab9a73c0f..7b8ad7d7af6 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -51,6 +51,7 @@ use ast::{SelfExplicit, SelfRegion, SelfStatic, SelfValue};
 use ast::{Delimited, SequenceRepetition, TokenTree, TraitItem, TraitRef};
 use ast::{TtDelimited, TtSequence, TtToken};
 use ast::{TupleVariantKind, Ty, Ty_, TypeBinding};
+use ast::{TyMac};
 use ast::{TyFixedLengthVec, TyBareFn, TyTypeof, TyInfer};
 use ast::{TyParam, TyParamBound, TyParen, TyPath, TyPolyTraitRef, TyPtr};
 use ast::{TyRptr, TyTup, TyU32, TyVec, UnUniq};
@@ -1369,8 +1370,20 @@ impl<'a> Parser<'a> {
         } else if self.check(&token::ModSep) ||
                   self.token.is_ident() ||
                   self.token.is_path() {
-            // NAMED TYPE
-            try!(self.parse_ty_path())
+            let path = try!(self.parse_path(LifetimeAndTypesWithoutColons));
+            if self.check(&token::Not) {
+                // MACRO INVOCATION
+                try!(self.bump());
+                let delim = try!(self.expect_open_delim());
+                let tts = try!(self.parse_seq_to_end(&token::CloseDelim(delim),
+                                                     seq_sep_none(),
+                                                     |p| p.parse_token_tree()));
+                let hi = self.span.hi;
+                TyMac(spanned(lo, hi, MacInvocTT(path, tts, EMPTY_CTXT)))
+            } else {
+                // NAMED TYPE
+                TyPath(None, path)
+            }
         } else if try!(self.eat(&token::Underscore) ){
             // TYPE TO BE INFERRED
             TyInfer
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index f0973e0ba6e..3b8ee91374c 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -734,6 +734,9 @@ impl<'a> State<'a> {
             ast::TyInfer => {
                 try!(word(&mut self.s, "_"));
             }
+            ast::TyMac(ref m) => {
+                try!(self.print_mac(m, token::Paren));
+            }
         }
         self.end()
     }
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 649052d123c..b32ed15b50f 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -405,6 +405,9 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty) {
             visitor.visit_expr(&**expression)
         }
         TyInfer => {}
+        TyMac(ref mac) => {
+            visitor.visit_mac(mac)
+        }
     }
 }