syntax: unify all MacResult's into a single trait.

There's now one unified way to return things from a macro, instead of
being able to choose the `AnyMacro` trait or the `MRItem`/`MRExpr`
variants of the `MacResult` enum. This does simplify the logic handling
the expansions, but the biggest value of this is it makes macros in (for
example) type position easier to implement, as there's this single thing
to modify.

By my measurements (using `-Z time-passes` on libstd and librustc etc.),
this appears to have little-to-no impact on expansion speed. There are
presumably larger costs than the small number of extra allocations and
virtual calls this adds (notably, all `macro_rules!`-defined macros have
not changed in behaviour, since they had to use the `AnyMacro` trait
anyway).

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libsyntax/ext/cfg.rs b/src/libsyntax/ext/cfg.rs
index d83a386554e..8cd899738bf 100644
--- a/src/libsyntax/ext/cfg.rs
+++ b/src/libsyntax/ext/cfg.rs
@@ -26,7 +26,7 @@ use parse::token::InternedString;
 use parse::token;
 use parse;
 
-pub fn expand_cfg(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree]) -> base::MacResult {
+pub fn expand_cfg(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree]) -> ~base::MacResult {
     let mut p = parse::new_parser_from_tts(cx.parse_sess(),
                                            cx.cfg(),
                                            tts.iter()
@@ -47,5 +47,5 @@ pub fn expand_cfg(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree]) -> base::M
     let matches_cfg = attr::test_cfg(cx.cfg().as_slice(),
                                      in_cfg.iter().map(|&x| x));
     let e = cx.expr_bool(sp, matches_cfg);
-    MRExpr(e)
+    MacExpr::new(e)
 }