From a9d84ab28a3e234d69c5bb7068d60d3f16c126fd Mon Sep 17 00:00:00 2001
From: Brian Anderson <banderson@mozilla.com>
Date: Tue, 5 Jul 2011 14:34:31 -0700
Subject: [PATCH] Make type unification failures non-fatal

Add a failure checkpoint after the typechecking pass. There are still many
fatal errors in typeck, but loosening up this one makes it easier to lean on
the compiler when making changes to types.

Issue #440.
---
 src/comp/middle/typeck.rs | 40 +++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/src/comp/middle/typeck.rs b/src/comp/middle/typeck.rs
index 214d2f9581e..330c1fd3884 100644
--- a/src/comp/middle/typeck.rs
+++ b/src/comp/middle/typeck.rs
@@ -942,29 +942,36 @@ mod demand {
             ty_param_subst_var_ids += [ty::ty_var_id(fcx.ccx.tcx, t_0)];
             simple(fcx, sp, ty_param_subst, t_0);
         }
+
+        fn mk_result(&@fn_ctxt fcx, &ty::t result_ty,
+                     &vec[int] ty_param_subst_var_ids,
+                     uint implicit_boxes) -> ty_param_substs_and_ty {
+            let vec[ty::t] result_ty_param_substs = [];
+            for (int var_id in ty_param_subst_var_ids) {
+                auto tp_subst = ty::mk_var(fcx.ccx.tcx, var_id);
+                result_ty_param_substs += [tp_subst];
+            }
+            ret tup(result_ty_param_substs,
+                    add_boxes(fcx.ccx, implicit_boxes, result_ty));
+        }
+
         alt (unify::simple(fcx, expected_1, actual_1)) {
             case (ures_ok(?t)) {
-                let vec[ty::t] result_ty_param_substs = [];
-                for (int var_id in ty_param_subst_var_ids) {
-                    auto tp_subst = ty::mk_var(fcx.ccx.tcx, var_id);
-                    result_ty_param_substs += [tp_subst];
-                }
-                ret tup(result_ty_param_substs,
-                        add_boxes(fcx.ccx, implicit_boxes, t));
+                ret mk_result(fcx, t, ty_param_subst_var_ids,
+                              implicit_boxes);
             }
             case (ures_err(?err)) {
                 auto e_err = resolve_type_vars_if_possible(fcx, expected_1);
                 auto a_err = resolve_type_vars_if_possible(fcx, actual_1);
-                fcx.ccx.tcx.sess.span_fatal(sp,
+                fcx.ccx.tcx.sess.span_err(sp,
                                           "mismatched types: expected " +
-                                              ty_to_str(fcx.ccx.tcx, e_err) +
-                                              " but found " +
-                                              ty_to_str(fcx.ccx.tcx, a_err) +
-                                              " (" + ty::type_err_to_str(err)
-                                              + ")");
-                // TODO: In the future, try returning "expected", reporting
-                // the error, and continue.
-
+                                          ty_to_str(fcx.ccx.tcx, e_err) +
+                                          " but found " +
+                                          ty_to_str(fcx.ccx.tcx, a_err) +
+                                          " (" + ty::type_err_to_str(err)
+                                          + ")");
+                ret mk_result(fcx, expected_1,
+                              ty_param_subst_var_ids, implicit_boxes);
             }
         }
     }
@@ -2502,6 +2509,7 @@ fn check_crate(&ty::ctxt tcx, &@ast::crate crate) {
         rec(visit_item_pre=bind check_item(ccx, _)
             with walk::default_visitor());
     walk::walk_crate(visit, *crate);
+    tcx.sess.abort_if_errors();
 }
 //
 // Local Variables: