[SYCL][NFC] Introduce unit-tests for ONEAPI_DEVICE_SELECTOR

There are E2E tests which are essentially testing the correctness of
`ONEAPI_DEVICE_SELECTOR` env variable testing, but that can be done in
way more efficient way which is unit-tests.

Note that this PR does not aim to cover `ONEAPI_DEVICE_SELECTOR` parsing
with unit-tests in full, but rather aims to replace the most obvious
candidates from E2E tests with unit-tests, providing some foundation for
expanding unit-tests in follow-up PRs.

Author: AlexeySachkov

sycl/include/sycl/detail/device_filter.hpp

@@ -53,6 +53,21 @@ struct ods_target {
   ods_target(backend be) { Backend = be; };
   ods_target(){};
   friend std::ostream &operator<<(std::ostream &Out, const ods_target &Target);
+
+#if __cplusplus >= 202002L
+  bool operator==(const ods_target &Other) const = default;
+#else
+  bool operator==(const ods_target &Other) const {
+    return Backend == Other.Backend && DeviceType == Other.DeviceType &&
+           HasDeviceWildCard == Other.HasDeviceWildCard &&
+           DeviceNum == Other.DeviceNum &&
+           HasSubDeviceWildCard == Other.HasSubDeviceWildCard &&
+           HasSubSubDeviceWildCard == Other.HasSubSubDeviceWildCard &&
+           SubSubDeviceNum == Other.SubSubDeviceNum &&
+           IsNegativeTarget == Other.IsNegativeTarget &&
+           MatchesSeen == Other.MatchesSeen;
+  }
+#endif
 };
 
 class ods_target_list {

sycl/test-e2e/OneapiDeviceSelector/backendonly_error.cpp

@@ -59,3 +59,4 @@ if (NOT WIN32)
 endif()
 add_subdirectory(sampler)
 add_subdirectory(reduction)
+add_subdirectory(OneAPIDeviceSelector)

sycl/test-e2e/OneapiDeviceSelector/case_sensitivity.cpp

@@ -0,0 +1,3 @@
+add_sycl_unittest(OneAPIDeviceSelectorTests OBJECT
+  Tests.cpp
+)

sycl/unittests/CMakeLists.txt

@@ -0,0 +1,57 @@
+//===---------------------------- Tests.cpp -------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <sycl/detail/device_filter.hpp>
+#include <sycl/exception.hpp>
+
+#include <gtest/gtest.h>
+
+#include <vector>
+#include <utility>
+#include <string>
+
+TEST(OneAPIDeviceSelector, IsCaseInsensitive) {
+  ASSERT_EQ(sycl::detail::Parse_ONEAPI_DEVICE_SELECTOR("OPENCL:*"),
+            sycl::detail::Parse_ONEAPI_DEVICE_SELECTOR("opencl:*"))
+      << " backend should be case-insensitive";
+
+  ASSERT_EQ(sycl::detail::Parse_ONEAPI_DEVICE_SELECTOR("*:GPU"),
+            sycl::detail::Parse_ONEAPI_DEVICE_SELECTOR("*:gpu"))
+      << " device type should be case-insensitive";
+}
+
+TEST(OneAPIDeviceSelector, EmitsErrorIfOnlyBackendIsSpecified) {
+  try {
+    std::ignore = sycl::detail::Parse_ONEAPI_DEVICE_SELECTOR("level_zero");
+    FAIL() << "An exception was expected";
+  } catch (const sycl::exception &e) {
+    ASSERT_EQ(e.code(), sycl::errc::invalid);
+    ASSERT_EQ(std::string(e.what()),
+              "Incomplete selector!  Try 'level_zero:*' if all "
+              "devices under the backend was original intention.");
+  }
+}
+
+TEST(OneAPIDeviceSelector, EmitsErrorIfBackendStringIsInvalid) {
+  try {
+    std::ignore = sycl::detail::Parse_ONEAPI_DEVICE_SELECTOR("macaroni:*");
+    FAIL() << "An exception was expected";
+  } catch (const sycl::exception &e) {
+    ASSERT_EQ(e.code(), sycl::errc::invalid);
+    // FIXME: the error below could be better
+    ASSERT_EQ(std::string(e.what()),
+              "ONEAPI_DEVICE_SELECTOR parsing error. Backend is required but "
+              "missing from \"macaroni:*\"");
+  }
+}
+
+// TODO: test case ":"
+// TODO: test case ":cpu"
+// TODO: test case "level_zero:cpu:cpu"
+// TODO: test case "opencl:"
+// TODO: other positive test cases for parsing device, sub-devices, etc.