Add helper to wrap result of std::filesystem::path::u8string() (#2535)

In C++17 the return type of std::filesystem::path::u8string() is
std::string, but in C++20 the return type changed to std::u8string.

Add a helper to copy a std::u8string to a std::string, to be used when a
std::string is required. This fixes the build for C++20.

test_common/harness/stringHelpers.h

@@ -39,4 +39,20 @@ inline std::string str_sprintf(const std::string &str, Args... args)
     return std::string(buffer.get(), buffer.get() + s - 1);
 }
 
+// Returns the argument, converted to std::string.
+// The return type of std::filesystem::path::u8string() was
+// std::string in C++17, but became std::u8string in C++20.
+// Use this method to wrap the result when a std::string
+// is desired.
+//
+// Use a template with a specialization for std::string,
+// so the generic template applies when std::u8string exists
+// and is used.
+template <typename STRING_TYPE>
+inline std::string to_string(const STRING_TYPE &str)
+{
+    return std::string(str.begin(), str.end());
+}
+inline std::string to_string(const std::string &str) { return str; }
+
 #endif // STRING_HELPERS_H

test_conformance/compiler/main.cpp

@@ -17,9 +17,10 @@
 #include <filesystem>
 
 #include "harness/testHarness.h"
+#include "harness/stringHelpers.h"
 
 std::string spvBinariesPath =
-    (std::filesystem::path("compiler") / "spirv_bin").u8string();
+    to_string((std::filesystem::path("compiler") / "spirv_bin").u8string());
 const std::string spvBinariesPathArg = "--spirv-binaries-path";
 
 void printUsage()

test_conformance/compiler/test_compile.cpp

@@ -24,6 +24,7 @@
 #include <unistd.h>
 #endif
 #include "harness/conversions.h"
+#include "harness/stringHelpers.h"
 
 #define MAX_LINE_SIZE_IN_PROGRAM 1024
 #define MAX_LOG_SIZE_IN_PROGRAM 2048
@@ -3059,12 +3060,13 @@ REGISTER_TEST(execute_after_included_header_link)
     }
 
     const auto simple_header_path = temp_dir_path / simple_header_name;
-    FILE *simple_header_file =
+    const std::string simple_header_path_str =
-        fopen(simple_header_path.u8string().c_str(), "w");
+        to_string(simple_header_path.u8string());
+    FILE *simple_header_file = fopen(simple_header_path_str.c_str(), "w");
     if (simple_header_file == NULL)
     {
         log_error("ERROR: Unable to create simple header file %s! (in %s:%d)\n",
-                  simple_header_path.u8string().c_str(), __FILE__, __LINE__);
+                  simple_header_path_str.c_str(), __FILE__, __LINE__);
         return -1;
     }
     if (fprintf(simple_header_file, "%s", simple_header) < 0)
@@ -3082,7 +3084,7 @@ REGISTER_TEST(execute_after_included_header_link)
     }
 
     const std::string include_path =
-        std::string("-I") + temp_dir_path.generic_u8string();
+        std::string("-I") + to_string(temp_dir_path.generic_u8string());
     error = clCompileProgram(program, 1, &device, include_path.c_str(), 0, NULL,
                              NULL, NULL, NULL);
     test_error(error,