Add a syntax extension to log syntax, for debugging macros.

src/comp/rustc.rc

@@ -49,6 +49,7 @@ mod middle {
 
 mod syntax {
     mod ast;
+
     mod fold;
     mod visit;
     mod codemap;
@@ -67,6 +68,7 @@ mod syntax {
         mod simplext;
         mod concat_idents;
         mod ident_to_str;
+        mod log_syntax;
     }
     mod print {
         mod pprust;

src/comp/syntax/ext/base.rs

@@ -29,6 +29,8 @@ fn syntax_expander_table() -> hashmap[str, syntax_extension] {
                             normal(ext::concat_idents::expand_syntax_ext));
     syntax_expanders.insert("ident_to_str",
                             normal(ext::ident_to_str::expand_syntax_ext));
+    syntax_expanders.insert("log_syntax",
+                            normal(ext::log_syntax::expand_syntax_ext));
     ret syntax_expanders;
 }
 
@@ -36,6 +38,8 @@ obj ext_ctxt(sess: @session, crate_file_name_hack: str,
              mutable backtrace: span[]) {
     fn crate_file_name() -> str { ret crate_file_name_hack; }
 
+    fn session() -> @session { ret sess; }
+
     fn print_backtrace() {
         for sp: span in backtrace {
             sess.span_note(sp, "(while expanding this)")

src/comp/syntax/ext/log_syntax.rs

@@ -0,0 +1,13 @@
+import std::option;
+import base::*;
+import syntax::ast;
+
+fn expand_syntax_ext(cx: &ext_ctxt, sp: codemap::span, arg: @ast::expr,
+                     body: option::t[str]) -> @ast::expr {
+
+    cx.print_backtrace();
+    std::io::stdout().write_line(print::pprust::expr_to_str(arg));
+
+    //trivial expression
+    ret @{id: cx.next_id(), node: ast::expr_rec(~[], option::none), span: sp};
+}