Don't create a new inference context for checking pattern ranges.

Ugly fix -- it would be better to refactor and consolidate the various
"make sure these types are the same" fns scattered around typeck.

src/rustc/middle/typeck.rs

@@ -203,6 +203,23 @@ fn require_same_types(
     }
 }
 
+fn require_same_types_in_infcx(
+    infcx: infer::infer_ctxt,
+    span: span,
+    t1: ty::t,
+    t2: ty::t,
+    msg: fn() -> str) -> bool {
+
+    alt infer::compare_tys_in_infcx(infcx, t1, t2) {
+      result::ok(()) { true }
+      result::err(terr) {
+        infcx.tcx.sess.span_err(span, msg() + ": " +
+            ty::type_err_to_str(infcx.tcx, terr));
+        false
+      }
+    }
+}
+
 fn arg_is_argv_ty(_tcx: ty::ctxt, a: ty::arg) -> bool {
     alt ty::get(a.ty).struct {
       ty::ty_vec(mt) {

src/rustc/middle/typeck/check/alt.rs

@@ -137,9 +137,12 @@ fn check_pat(pcx: pat_ctxt, pat: @ast::pat, expected: ty::t) {
         check_expr_with(fcx, end, expected);
         let b_ty =
             fcx.infcx.resolve_type_vars_if_possible(fcx.expr_ty(begin));
-        if !require_same_types(
-            tcx, pat.span, b_ty,
-            fcx.infcx.resolve_type_vars_if_possible(fcx.expr_ty(end)),
+        let e_ty =
+            fcx.infcx.resolve_type_vars_if_possible(fcx.expr_ty(end));
+        #debug["pat_range beginning type: %?", b_ty];
+        #debug["pat_range ending type: %?", e_ty];
+        if !require_same_types_in_infcx(
+            fcx.infcx, pat.span, b_ty, e_ty,
             {|| "mismatched types in range" }) {
             // no-op
         } else if !ty::type_is_numeric(b_ty) {

src/rustc/middle/typeck/infer.rs

@@ -172,6 +172,7 @@ export resolve_deep_var;
 export methods; // for infer_ctxt
 export unify_methods; // for infer_ctxt
 export compare_tys;
+export compare_tys_in_infcx;
 export fixup_err, fixup_err_to_str;
 export assignment;
 export root, to_str;
@@ -381,6 +382,10 @@ fn compare_tys(tcx: ty::ctxt, a: ty::t, b: ty::t) -> ures {
     mk_eqty(infcx, a, b)
 }
 
+fn compare_tys_in_infcx(infcx: infer_ctxt, a: ty::t, b: ty::t) -> ures {
+    mk_eqty(infcx, a, b)
+}
+
 // See comment on the type `resolve_state` below
 fn resolve_shallow(cx: infer_ctxt, a: ty::t,
                    force_vars: force_level) -> fres<ty::t> {