[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/test/basic_tests/sycl_string.cpp

@@ -0,0 +1,77 @@
+// RUN: %clangxx -fsycl %s -o %t.out
+// RUN: %t.out
+#include <sycl/sycl.hpp>
+
+int main() {
+  // Default constructor
+  sycl::detail::string empty_s;
+  assert(empty_s.empty() && "Default constructed string should be empty");
+  assert(strcmp(empty_s.c_str(), "") == 0 &&
+         "Default constructed string should be empty string");
+
+  // std::string_view constructor
+  std::string_view sv = "Hello, World!";
+  sycl::detail::string s1(sv);
+  assert(strcmp(s1.c_str(), "Hello, World!") == 0 &&
+         "String from string_view constructor should match view content");
+
+  // Copy constructor
+  sycl::detail::string s2(s1);
+  assert(strcmp(s2.c_str(), "Hello, World!") == 0 &&
+         "Copied string should match original");
+  // Check for deep copy
+  s1 = "Changed";
+  assert(strcmp(s2.c_str(), "Hello, World!") == 0 &&
+         "Copied string should be a deep copy");
+
+  // Move constructor
+  sycl::detail::string s3(std::move(s1));
+  assert(strcmp(s3.c_str(), "Changed") == 0 &&
+         "Moved string should have original content");
+
+  // string_view assignment
+  sycl::detail::string s4;
+  s4 = "New String";
+  assert(strcmp(s4.c_str(), "New String") == 0 &&
+         "String_view assignment should update content");
+
+  // Copy assignment
+  sycl::detail::string s5;
+  s5 = s2;
+  assert(strcmp(s5.c_str(), "Hello, World!") == 0 &&
+         "Copy assignment should work correctly");
+
+  // Move assignment
+  sycl::detail::string s6;
+  s6 = std::move(s3);
+  assert(strcmp(s6.c_str(), "Changed") == 0 &&
+         "Move assignment should work correctly");
+
+  // Test c_str() and data()
+  assert(strcmp(s6.data(), "Changed") == 0 &&
+         "data() should return same as c_str()");
+
+  // Test empty(). Thrice.
+  sycl::detail::string s_not_empty("not empty");
+  sycl::detail::string s_empty;
+  assert(!s_not_empty.empty() && "String with content should not be empty");
+  assert(sycl::detail::string("").empty() && "Empty string should be empty");
+  assert(s_empty.empty() && "Default constructed string should be empty");
+
+  // Test swap.
+  sycl::detail::string swap_s1("first");
+  sycl::detail::string swap_s2("second");
+  swap(swap_s1, swap_s2);
+  assert(strcmp(swap_s1.c_str(), "second") == 0 &&
+         "swap should exchange content");
+  assert(strcmp(swap_s2.c_str(), "first") == 0 &&
+         "swap should exchange content");
+
+  // Comparison operators
+  sycl::detail::string compare_s("match");
+  assert((compare_s == "match") && "string == string_view should work");
+  assert(("match" == compare_s) && "string_view == string should work");
+  assert(!(compare_s == "no match") && "string == string_view should fail");
+
+  return 0;
+}