From 966504c828ded5b6a0a9d4ff5264fb778570005e Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Fri, 3 Feb 2012 17:10:29 -0800
Subject: [PATCH] don't fail if inference is not complete

---
 src/comp/middle/ty.rs  |  1 +
 src/comp/util/ppaux.rs | 17 ++++++++++++-----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/comp/middle/ty.rs b/src/comp/middle/ty.rs
index 02f687cb615..0826eda4cf3 100644
--- a/src/comp/middle/ty.rs
+++ b/src/comp/middle/ty.rs
@@ -167,6 +167,7 @@ export type_structurally_contains;
 export type_structurally_contains_uniques;
 export type_autoderef;
 export type_param;
+export canon_mode;
 export resolved_mode;
 export arg_mode;
 export unify_mode;
diff --git a/src/comp/util/ppaux.rs b/src/comp/util/ppaux.rs
index 512b02ca734..969195a40ac 100644
--- a/src/comp/util/ppaux.rs
+++ b/src/comp/util/ppaux.rs
@@ -12,12 +12,19 @@ import middle::ast_map;
 fn ty_to_str(cx: ctxt, typ: t) -> str {
     fn fn_input_to_str(cx: ctxt, input: {mode: ast::mode, ty: t}) ->
        str {
-        let arg_mode = ty::arg_mode(cx, input);
-        let modestr = {
-            if arg_mode == ty::default_arg_mode_for_ty(cx, input.ty) { "" }
-            else { mode_to_str(input.mode) }
+        let {mode, ty} = input;
+        let modestr = alt canon_mode(cx, mode) {
+          ast::infer(_) { "" }
+          ast::expl(m) {
+            if !ty::type_contains_vars(cx, ty) &&
+                m == ty::default_arg_mode_for_ty(cx, ty) {
+                ""
+            } else {
+                mode_to_str(ast::expl(m))
+            }
+          }
         };
-        modestr + ty_to_str(cx, input.ty)
+        modestr + ty_to_str(cx, ty)
     }
     fn fn_to_str(cx: ctxt, proto: ast::proto, ident: option<ast::ident>,
                  inputs: [arg], output: t, cf: ast::ret_style,