refactor Method definition to make space for macros

This change propagates to many locations, but because of the
Macro Exterminator (or, more properly, the invariant that it
protects), macro invocations can't occur downstream of expansion.
This means that in librustc and librustdoc, extracting the
desired field can simply assume that it can't be a macro
invocation. Functions in ast_util abstract over this check.

src/libsyntax/ast.rs

@@ -633,6 +633,8 @@ pub type Mac = Spanned<Mac_>;
 /// There's only one flavor, now, so this could presumably be simplified.
 #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash)]
 pub enum Mac_ {
+    // NB: the additional ident for a macro_rules-style macro is actually
+    // stored in the enclosing item. Oog.
     MacInvocTT(Path, Vec<TokenTree> , SyntaxContext),   // new macro-invocation
 }
 
@@ -950,19 +952,20 @@ pub enum ExplicitSelf_ {
 
 pub type ExplicitSelf = Spanned<ExplicitSelf_>;
 
-// Represents a method declaration
 #[deriving(PartialEq, Eq, Encodable, Decodable, Hash)]
 pub struct Method {
-    pub ident: Ident,
     pub attrs: Vec<Attribute>,
-    pub generics: Generics,
-    pub explicit_self: ExplicitSelf,
-    pub fn_style: FnStyle,
-    pub decl: P<FnDecl>,
-    pub body: P<Block>,
     pub id: NodeId,
     pub span: Span,
-    pub vis: Visibility,
+    pub node: Method_
+}
+
+#[deriving(PartialEq, Eq, Encodable, Decodable, Hash)]
+pub enum Method_ {
+    /// Represents a method declaration
+    MethDecl(Ident, Generics, ExplicitSelf, FnStyle, P<FnDecl>, P<Block>, Visibility),
+    /// Represents a macro in method position
+    MethMac(Mac),
 }
 
 #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash)]