Fix golden tests to use the "target" Bazel configuration (#581)

In practice, this means that `executable_semantics` will be built and run using the configuration specified on the command line, rather than e.g. always using `-c opt`.

Also fix a bug exposed by this change.

bazel/testing/BUILD

@@ -2,4 +2,4 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-exports_files(["golden_test.sh"])
+exports_files(["golden_test.py"])

bazel/testing/golden_test.bzl

@@ -4,22 +4,27 @@
 
 """Rule for a golden test."""
 
-def golden_test(name, golden, subject, **kwargs):
+def golden_test(name, golden, cmd, data, **kwargs):
     """Compares two files. Passes if they are identical.
 
     Args:
       name: Name of the build rule.
-      subject: The generated file to be compared.
-      golden: The golden file to be compared.
-      **kwargs: Any additional parameters for the generated sh_test.
+      cmd: The command whose output is being tested.
+      golden: The golden file to be compared against the command output.
+      **kwargs: Any additional parameters for the generated py_test.
     """
-    native.sh_test(
+    native.py_test(
         name = name,
-        srcs = ["//bazel/testing:golden_test.sh"],
+        srcs = ["//bazel/testing:golden_test.py"],
+        main = "//bazel/testing:golden_test.py",
         args = [
             "$(location %s)" % golden,
-            "$(location %s)" % subject,
+            cmd,
         ],
-        data = [golden, subject],
+        data = [golden] + data,
+        env = {
+            # TODO(#580): Remove this when leaks are fixed.
+            "ASAN_OPTIONS": "detect_leaks=0",
+        },
         **kwargs
     )

bazel/testing/golden_test.py

@@ -0,0 +1,81 @@
+#!/usr/bin/env python3
+
+"""Compare a command's output against an expected "golden" output file.
+
+Usage:
+
+golden_test.py <golden path> <command> [--update]
+
+<golden path> is the path to the golden file, and <command> is
+the command to run, including any arguments. If --update is specified,
+the command will be run and its output stored in the golden file.
+Otherwise, the command will be run and its output compared against
+the contents of the golden file.
+
+For these purposes, the command's output consists of the interleaved
+contents of stdout and stderr, as well as the command's exit code. Thus,
+golden tests can provide coverage of cases where the command is expected
+to fail, as well as cases where it's expected to succeed.
+
+This script is designed to be run by a `golden_test` Bazel rule,
+and may not work when run outside that context.
+"""
+
+__copyright__ = """
+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
+"""
+
+import os
+import subprocess
+import sys
+
+golden_path = sys.argv[1]
+subject_cmd_args = sys.argv[2].split()
+
+subject_cmd = subprocess.run(
+    args=subject_cmd_args,
+    stdout=subprocess.PIPE,  # Capture stdout as a string
+    stderr=subprocess.STDOUT,  # Send stderr to the same place as stdout
+    universal_newlines=True,
+)
+
+subject = subject_cmd.stdout
+if subject_cmd.returncode != 0:
+    subject += "EXIT CODE: {0}\n".format(subject_cmd.returncode)
+
+if len(sys.argv) == 4 and sys.argv[3] == "--update":
+    with open(golden_path, "w") as golden:
+        golden.write(subject)
+        sys.exit(0)
+
+# TODO: consider using difflib instead of a subprocess
+diff_cmd = subprocess.run(
+    args=["diff", "-u", golden_path, "-"],
+    input=subject,
+    universal_newlines=True,
+)
+if diff_cmd.returncode == 0:
+    print("PASS")
+    sys.exit(0)
+
+error_output = """When running under:
+  {dir}
+the golden contents of:
+  {golden_path}
+do not match generated output of:
+  {subject_cmd_args}
+
+To update the golden file, run the following:
+
+  bazel run ${test_target} -- --update
+""".format(
+    dir=os.getenv("TEST_SRCDIR"),
+    golden_path=golden_path,
+    subject_cmd_args=sys.argv[2],
+    test_target=os.getenv("TEST_TARGET"),
+)
+
+print(error_output)
+sys.exit(1)

bazel/testing/golden_test.sh

@@ -1,36 +0,0 @@
-#!/bin/bash
-# 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
-
-set -e -u -o pipefail
-
-GOLDEN=$1
-SUBJECT=$2
-
-if [[ $# == 3 && $3 == "--update" ]]; then
-  cp "${SUBJECT}" "${GOLDEN}"
-  exit $?
-fi
-
-CMD=("diff" "-u" "${GOLDEN}" "${SUBJECT}")
-
-if "${CMD[@]}"; then
-  echo "PASS"
-  exit 0
-fi
-
-cat <<EOT
-When running under:
-  ${TEST_SRCDIR}
-the golden contents of:
-  ${GOLDEN}
-do not match generated target:
-  ${SUBJECT}
-
-To update the golden file, run the following:
-
-  bazel run ${TEST_TARGET} -- --update
-EOT
-
-exit 1

executable_semantics/BUILD

@@ -92,17 +92,12 @@ EXAMPLES = [
     "experimental_continuation9",
 ]
 
-[genrule(
-    name = "%s_out" % e,
-    srcs = ["testdata/%s.carbon" % e],
-    outs = ["testdata/%s.out" % e],
-    # Suppress command errors.
-    cmd = "$(location executable_semantics) $< > $@ 2>&1 || echo EXIT CODE: $$? >> $@",
-    tools = [":executable_semantics"],
-) for e in EXAMPLES]
-
 [golden_test(
     name = "%s_test" % e,
+    cmd = "'$(location executable_semantics) $(location testdata/%s.carbon)'" % e,
+    data = [
+        ":executable_semantics",
+        "testdata/%s.carbon" % e,
+    ],
     golden = "testdata/%s.golden" % e,
-    subject = "testdata/%s.out" % e,
 ) for e in EXAMPLES]

executable_semantics/interpreter/typecheck.cpp

@@ -149,8 +149,8 @@ auto TypeCheckExp(const Expression* e, TypeEnv types, Env values,
       return TCResult(new_e, t, types);
     }
     case ExpressionKind::Index: {
-      auto res = TypeCheckExp(e->GetFieldAccess().aggregate, types, values,
-                              nullptr, TCContext::ValueContext);
+      auto res = TypeCheckExp(e->GetIndex().aggregate, types, values, nullptr,
+                              TCContext::ValueContext);
       auto t = res.type;
       switch (t->tag) {
         case ValKind::TupleV: {

executable_semantics/syntax/BUILD

@@ -47,7 +47,7 @@ cc_test(
     name = "paren_contents_test",
     srcs = ["paren_contents_test.cpp"],
     env = {
-        # FIXME: Remove this when leaks are fixed.
+        # TODO(#580): Remove this when leaks are fixed.
         "ASAN_OPTIONS": "detect_leaks=0",
     },
     deps = [