[SYCL] Fix for sycl::detail::string and tests

sycl/include/sycl/detail/string.hpp

@@ -58,7 +58,7 @@ class string {
 
   const char *c_str() const noexcept { return str ? str : ""; }
   const char *data() const noexcept { return c_str(); }
-  bool empty() { return str ? str[0] : false; }
+  bool empty() const noexcept { return str == nullptr || *str == '\0'; }
 
   friend bool operator==(const string &lhs, std::string_view rhs) noexcept {
     return rhs == lhs.c_str();

sycl/unittests/misc/CMakeLists.txt

@@ -6,6 +6,7 @@ add_sycl_unittest(MiscTests SHARED
   CircularBuffer.cpp
   OsUtils.cpp
   PropertyUtils.cpp
+  SYCLString.cpp
 )
 endif()
 add_subdirectory(LinkGraph)

sycl/unittests/misc/SYCLString.cpp

@@ -0,0 +1,89 @@
+#include <gtest/gtest.h>
+#include <sycl/sycl.hpp>
+
+class SYCLDetailStringTest : public ::testing::Test {};
+
+TEST_F(SYCLDetailStringTest, DefaultConstructor) {
+  sycl::detail::string empty_s;
+  EXPECT_TRUE(empty_s.empty());
+  EXPECT_STREQ(empty_s.c_str(), "");
+}
+
+TEST_F(SYCLDetailStringTest, StringViewConstructor) {
+  std::string_view sv = "Hello, World!";
+  sycl::detail::string s1(sv);
+  EXPECT_STREQ(s1.c_str(), "Hello, World!");
+}
+
+TEST_F(SYCLDetailStringTest, CopyConstructor) {
+  sycl::detail::string s1("Hello, World!");
+  sycl::detail::string s2(s1);
+  EXPECT_STREQ(s2.c_str(), "Hello, World!");
+
+  // Check for deep copy: modifying the original should not affect the copy.
+  s1 = "Changed";
+  EXPECT_STREQ(s2.c_str(), "Hello, World!");
+}
+
+TEST_F(SYCLDetailStringTest, MoveConstructor) {
+  sycl::detail::string s1("Changed");
+  sycl::detail::string s2(std::move(s1));
+  EXPECT_STREQ(s2.c_str(), "Changed");
+}
+
+TEST_F(SYCLDetailStringTest, StringViewAssignment) {
+  sycl::detail::string s;
+  s = "New String";
+  EXPECT_STREQ(s.c_str(), "New String");
+}
+
+TEST_F(SYCLDetailStringTest, CopyAssignment) {
+  sycl::detail::string s1("Hello, World!");
+  sycl::detail::string s2;
+  s2 = s1;
+  EXPECT_STREQ(s2.c_str(), "Hello, World!");
+
+  // Check for deep copy.
+  s1 = "Changed";
+  EXPECT_STREQ(s2.c_str(), "Hello, World!");
+}
+
+TEST_F(SYCLDetailStringTest, MoveAssignment) {
+  sycl::detail::string s1("Changed");
+  sycl::detail::string s2;
+  s2 = std::move(s1);
+  EXPECT_STREQ(s2.c_str(), "Changed");
+}
+
+TEST_F(SYCLDetailStringTest, Methods) {
+  sycl::detail::string s_not_empty("not empty");
+  sycl::detail::string s_empty;
+  // Test c_str() and data().
+  EXPECT_STREQ(s_not_empty.data(), "not empty");
+  EXPECT_STREQ(s_not_empty.c_str(), "not empty");
+  EXPECT_EQ(s_not_empty.data(), s_not_empty.c_str());
+
+  // Test empty(). Like really.
+  EXPECT_FALSE(s_not_empty.empty());
+  EXPECT_TRUE(sycl::detail::string("").empty());
+  EXPECT_TRUE(sycl::detail::string().empty());
+  EXPECT_TRUE(s_empty.empty());
+}
+
+TEST_F(SYCLDetailStringTest, Swap) {
+  sycl::detail::string s1("first");
+  sycl::detail::string s2("second");
+  swap(s1, s2);
+  EXPECT_STREQ(s1.c_str(), "second");
+  EXPECT_STREQ(s2.c_str(), "first");
+}
+
+TEST_F(SYCLDetailStringTest, ComparisonOperators) {
+  sycl::detail::string s("match");
+  std::string_view sv_match("match");
+  std::string_view sv_no_match("no match");
+
+  EXPECT_EQ(s, sv_match);
+  EXPECT_EQ(sv_match, s);
+  EXPECT_FALSE(s == sv_no_match);
+}