Replace LetSyntaxTT with MacroRulesTT

The implementation of LetSyntaxTT was specialized to macro_rules! in various
ways. This gets rid of the false generality and simplifies the code.

3 files changed, 30 insertions, 57 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 91cc8a24622..4b38e6c0cb2 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -328,13 +328,8 @@ pub enum SyntaxExtension {
     ///
     IdentTT(Box<IdentMacroExpander + 'static>, Option<Span>),
 
-    /// An ident macro that has two properties:
-    /// - it adds a macro definition to the environment, and
-    /// - the definition it adds doesn't introduce any new
-    ///   identifiers.
-    ///
-    /// `macro_rules!` is a LetSyntaxTT
-    LetSyntaxTT(Box<IdentMacroExpander + 'static>, Option<Span>),
+    /// Represents `macro_rules!` itself.
+    MacroRulesTT,
 }
 
 pub type NamedSyntaxExtension = (Name, SyntaxExtension);
@@ -364,8 +359,7 @@ fn initial_syntax_expander_table(ecfg: &expand::ExpansionConfig) -> SyntaxEnv {
     }
 
     let mut syntax_expanders = SyntaxEnv::new();
-    syntax_expanders.insert(intern("macro_rules"),
-                            LetSyntaxTT(box ext::tt::macro_rules::add_new_extension, None));
+    syntax_expanders.insert(intern("macro_rules"), MacroRulesTT);
     syntax_expanders.insert(intern("fmt"),
                             builtin_normal_expander(
                                 ext::fmt::expand_syntax_ext));
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index b3f30dd4581..a1a13f23064 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -7,7 +7,6 @@
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
-use self::Either::*;
 
 use ast::{Block, Crate, DeclLocal, ExprMac, PatMac};
 use ast::{Local, Ident, MacInvocTT};
@@ -18,6 +17,7 @@ use ast;
 use ast_util::path_to_ident;
 use ext::mtwt;
 use ext::build::AstBuilder;
+use ext::tt::macro_rules;
 use attr;
 use attr::AttrMetaMethods;
 use codemap;
@@ -33,11 +33,6 @@ use util::small_vector::SmallVector;
 use visit;
 use visit::Visitor;
 
-enum Either<L,R> {
-    Left(L),
-    Right(R)
-}
-
 pub fn expand_type(t: P<ast::Ty>,
                    fld: &mut MacroExpander,
                    impl_ty: Option<P<ast::Ty>>)
@@ -548,8 +543,8 @@ pub fn expand_item_mac(it: P<ast::Item>, fld: &mut MacroExpander)
 
     let extnamestr = token::get_ident(extname);
     let fm = fresh_mark();
-    let def_or_items = {
-        let mut expanded = match fld.cx.syntax_env.find(&extname.name) {
+    let items = {
+        let expanded = match fld.cx.syntax_env.find(&extname.name) {
             None => {
                 fld.cx.span_err(path_span,
                                 format!("macro undefined: '{}!'",
@@ -600,11 +595,10 @@ pub fn expand_item_mac(it: P<ast::Item>, fld: &mut MacroExpander)
                     let marked_tts = mark_tts(tts[], fm);
                     expander.expand(fld.cx, it.span, it.ident, marked_tts)
                 }
-                LetSyntaxTT(ref expander, span) => {
+                MacroRulesTT => {
                     if it.ident.name == parse::token::special_idents::invalid.name {
                         fld.cx.span_err(path_span,
-                                        format!("macro {}! expects an ident argument",
-                                                extnamestr.get())[]);
+                                        format!("macro_rules! expects an ident argument")[]);
                         return SmallVector::zero();
                     }
                     fld.cx.bt_push(ExpnInfo {
@@ -612,11 +606,21 @@ pub fn expand_item_mac(it: P<ast::Item>, fld: &mut MacroExpander)
                         callee: NameAndSpan {
                             name: extnamestr.get().to_string(),
                             format: MacroBang,
-                            span: span
+                            span: None,
                         }
                     });
-                    // DON'T mark before expansion:
-                    expander.expand(fld.cx, it.span, it.ident, tts)
+                    // DON'T mark before expansion.
+                    let MacroDef { name, ext }
+                        = macro_rules::add_new_extension(fld.cx, it.span, it.ident, tts);
+
+                    fld.cx.syntax_env.insert(intern(name.as_slice()), ext);
+                    if attr::contains_name(it.attrs.as_slice(), "macro_export") {
+                        fld.cx.exported_macros.push(it);
+                    }
+
+                    // macro_rules! has a side effect but expands to nothing.
+                    fld.cx.bt_pop();
+                    return SmallVector::zero();
                 }
                 _ => {
                     fld.cx.span_err(it.span,
@@ -627,31 +631,17 @@ pub fn expand_item_mac(it: P<ast::Item>, fld: &mut MacroExpander)
             }
         };
 
-        match expanded.make_def() {
-            Some(def) => Left(def),
-            None => Right(expanded.make_items())
-        }
+        expanded.make_items()
     };
 
-    let items = match def_or_items {
-        Left(MacroDef { name, ext }) => {
-            // hidden invariant: this should only be possible as the
-            // result of expanding a LetSyntaxTT, and thus doesn't
-            // need to be marked. Not that it could be marked anyway.
-            // create issue to recommend refactoring here?
-            fld.cx.syntax_env.insert(intern(name[]), ext);
-            if attr::contains_name(it.attrs[], "macro_export") {
-                fld.cx.exported_macros.push(it);
-            }
-            SmallVector::zero()
-        }
-        Right(Some(items)) => {
+    let items = match items {
+        Some(items) => {
             items.into_iter()
                 .map(|i| mark_item(i, fm))
                 .flat_map(|i| fld.fold_item(i).into_iter())
                 .collect()
         }
-        Right(None) => {
+        None => {
             fld.cx.span_err(path_span,
                             format!("non-item macro in item position: {}",
                                     extnamestr.get())[]);
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 08014dc1338..15b75442ca2 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -129,15 +129,6 @@ impl TTMacroExpander for MacroRulesMacroExpander {
     }
 }
 
-struct MacroRulesDefiner {
-    def: Option<MacroDef>
-}
-impl MacResult for MacroRulesDefiner {
-    fn make_def(&mut self) -> Option<MacroDef> {
-        Some(self.def.take().expect("empty MacroRulesDefiner"))
-    }
-}
-
 /// Given `lhses` and `rhses`, this is the new macro we create
 fn generic_extension<'cx>(cx: &'cx ExtCtxt,
                           sp: Span,
@@ -219,7 +210,7 @@ pub fn add_new_extension<'cx>(cx: &'cx mut ExtCtxt,
                               sp: Span,
                               name: Ident,
                               arg: Vec<ast::TokenTree> )
-                              -> Box<MacResult+'cx> {
+                              -> MacroDef {
 
     let lhs_nm =  gensym_ident("lhs");
     let rhs_nm =  gensym_ident("rhs");
@@ -279,10 +270,8 @@ pub fn add_new_extension<'cx>(cx: &'cx mut ExtCtxt,
         rhses: rhses,
     };
 
-    box MacroRulesDefiner {
-        def: Some(MacroDef {
-            name: token::get_ident(name).to_string(),
-            ext: NormalTT(exp, Some(sp))
-        })
-    } as Box<MacResult+'cx>
+    MacroDef {
+        name: token::get_ident(name).to_string(),
+        ext: NormalTT(exp, Some(sp))
+    }
 }