From f50a582126e35300bba5a3a8bec001ae6c301ed5 Mon Sep 17 00:00:00 2001
From: Paul Stansifer <paul.stansifer@gmail.com>
Date: Mon, 8 Aug 2011 14:17:33 -0700
Subject: [PATCH] Add a syntax extension to log syntax, for debugging macros.

---
 src/comp/rustc.rc                 |  2 ++
 src/comp/syntax/ext/base.rs       | 10 +++++++---
 src/comp/syntax/ext/log_syntax.rs | 13 +++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)
 create mode 100644 src/comp/syntax/ext/log_syntax.rs

diff --git a/src/comp/rustc.rc b/src/comp/rustc.rc
index e47c6337e32..a0505f870b4 100644
--- a/src/comp/rustc.rc
+++ b/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;
diff --git a/src/comp/syntax/ext/base.rs b/src/comp/syntax/ext/base.rs
index 5aad9c5cd14..62c480ad96b 100644
--- a/src/comp/syntax/ext/base.rs
+++ b/src/comp/syntax/ext/base.rs
@@ -29,19 +29,23 @@ 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;
 }
 
-obj ext_ctxt(sess: @session, crate_file_name_hack: str, 
+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)")
         }
     }
-    
+
     fn bt_push(sp: span) { backtrace += ~[sp]; }
     fn bt_pop() { ivec::pop(backtrace); }
 
@@ -59,7 +63,7 @@ obj ext_ctxt(sess: @session, crate_file_name_hack: str,
     }
     fn span_bug(sp:span, msg: str) -> ! {
         self.print_backtrace();
-        sess.span_bug(sp, msg); 
+        sess.span_bug(sp, msg);
     }
     fn bug(msg: str) -> ! {
         self.print_backtrace();
diff --git a/src/comp/syntax/ext/log_syntax.rs b/src/comp/syntax/ext/log_syntax.rs
new file mode 100644
index 00000000000..9cd745f07f7
--- /dev/null
+++ b/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};
+}
\ No newline at end of file