From 6824f119fcaef80e6ac377e887cbe6789e587f77 Mon Sep 17 00:00:00 2001
From: Brian Anderson <andersrb@gmail.com>
Date: Fri, 13 May 2011 14:42:23 -0400
Subject: [PATCH] rustc: Allow alt expressions to fail

---
 src/comp/middle/typeck.rs          | 12 +++++++++---
 src/test/run-fail/expr-alt-fail.rs | 13 +++++++++++++
 src/test/run-pass/expr-alt-fail.rs | 30 ++++++++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 3 deletions(-)
 create mode 100644 src/test/run-fail/expr-alt-fail.rs
 create mode 100644 src/test/run-pass/expr-alt-fail.rs

diff --git a/src/comp/middle/typeck.rs b/src/comp/middle/typeck.rs
index 6a37d1d22eba..aedbb89f2a8a 100644
--- a/src/comp/middle/typeck.rs
+++ b/src/comp/middle/typeck.rs
@@ -1457,7 +1457,10 @@ mod Pushdown {
                 for (ast::arm arm_0 in arms_0) {
                     pushdown_block(scx, expected, arm_0.block);
                     auto bty = block_ty(scx.fcx.ccx.tcx, arm_0.block);
-                    t = Demand::simple(scx, e.span, t, bty);
+                    // Failing alt arms don't need to have a matching type
+                    if (!ty::type_is_bot(scx.fcx.ccx.tcx, bty)) {
+                        t = Demand::simple(scx, e.span, t, bty);
+                    }
                 }
                 write::ty_only_fixup(scx, ann.id, t);
             }
@@ -2209,8 +2212,11 @@ fn check_expr(&@stmt_ctxt scx, &@ast::expr expr) {
                 check_block(scx, arm.block);
 
                 auto bty = block_ty(scx.fcx.ccx.tcx, arm.block);
-                result_ty = Demand::simple(scx, arm.block.span, result_ty,
-                                           bty);
+                // Failing alt arms don't need to have a matching type
+                if (!ty::type_is_bot(scx.fcx.ccx.tcx, bty)) {
+                    result_ty = Demand::simple(scx, arm.block.span,
+                                               result_ty, bty);
+                }
             }
 
             auto i = 0u;
diff --git a/src/test/run-fail/expr-alt-fail.rs b/src/test/run-fail/expr-alt-fail.rs
new file mode 100644
index 000000000000..33d09cce8c0f
--- /dev/null
+++ b/src/test/run-fail/expr-alt-fail.rs
@@ -0,0 +1,13 @@
+// xfail-stage0
+// error-pattern:explicit failure
+
+fn main() {
+  auto x = alt(true) {
+    case (false) {
+      0
+    }
+    case (true) {
+      fail
+    }
+  };
+}
diff --git a/src/test/run-pass/expr-alt-fail.rs b/src/test/run-pass/expr-alt-fail.rs
new file mode 100644
index 000000000000..373e0f02b369
--- /dev/null
+++ b/src/test/run-pass/expr-alt-fail.rs
@@ -0,0 +1,30 @@
+// xfail-stage0
+
+fn test_simple() {
+  auto r = alt (true) {
+    case (true) {
+      true
+    }
+    case (false) {
+      fail
+    }
+  };
+  assert (r == true);
+}
+
+fn test_box() {
+  auto r = alt (true) {
+    case (true) {
+      [10]
+    }
+    case (false) {
+      fail
+    }
+  };
+  assert (r.(0) == 10);
+}
+
+fn main() {
+  test_simple();
+  test_box();
+}