From fb0c0b63bfa2cf6baecb5d270a1b8d4e78531819 Mon Sep 17 00:00:00 2001
From: Geoff Romer <gromer@google.com>
Date: Tue, 27 Jul 2021 11:14:10 -0700
Subject: [PATCH] Fix `match` bug when no `case` matches (#677)

---
 executable_semantics/interpreter/interpreter.cpp |  2 +-
 executable_semantics/test_list.bzl               |  1 +
 executable_semantics/testdata/no_match.carbon    | 12 ++++++++++++
 executable_semantics/testdata/no_match.golden    |  1 +
 4 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 executable_semantics/testdata/no_match.carbon
 create mode 100644 executable_semantics/testdata/no_match.golden

diff --git a/executable_semantics/interpreter/interpreter.cpp b/executable_semantics/interpreter/interpreter.cpp
index b6ec23ef63c1..244b23df7030 100644
--- a/executable_semantics/interpreter/interpreter.cpp
+++ b/executable_semantics/interpreter/interpreter.cpp
@@ -854,7 +854,7 @@ void StepStmt() {
             clause_num = (act->pos - 1) / 2;
             if (clause_num ==
                 static_cast<int>(stmt->GetMatch().clauses->size())) {
-              frame->todo.Pop(2);
+              frame->todo.Pop(1);
             }
           }
         }
diff --git a/executable_semantics/test_list.bzl b/executable_semantics/test_list.bzl
index 84136a9def3b..cc4989e374ee 100644
--- a/executable_semantics/test_list.bzl
+++ b/executable_semantics/test_list.bzl
@@ -59,6 +59,7 @@ TEST_LIST = [
     "match_placeholder",
     "match_type",
     "next",
+    "no_match",
     "pattern_init",
     "pattern_variable_fail",
     "placeholder_variable",
diff --git a/executable_semantics/testdata/no_match.carbon b/executable_semantics/testdata/no_match.carbon
new file mode 100644
index 000000000000..fc9b2bc4b431
--- /dev/null
+++ b/executable_semantics/testdata/no_match.carbon
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+fn main() -> Int {
+  var x: Int = 0;
+  match (x) {
+    case 1 =>
+      return 1;
+  }
+  return 0;
+}
diff --git a/executable_semantics/testdata/no_match.golden b/executable_semantics/testdata/no_match.golden
new file mode 100644
index 000000000000..2db2755da426
--- /dev/null
+++ b/executable_semantics/testdata/no_match.golden
@@ -0,0 +1 @@
+result: 0