chore(core): update core to C++17

- use utfcodec.hpp's convert<>() instead of codecvt

Fixes: #8800

core/meson.build

@@ -9,7 +9,7 @@ project('keyman_core', 'cpp', 'c',
         version: run_command(find_program('getversion.bat', 'getversion.sh'), check:true).stdout().strip(),
         license: 'MIT',
         default_options : ['buildtype=release',
-                           'cpp_std=c++14',
+                           'cpp_std=c++17',
                            'b_vscrt=static_from_buildtype',
                            'warning_level=2',
                            'debug=true'],

core/src/km_core_state_api.cpp

@@ -13,7 +13,6 @@
 #include <sstream>
 #include <memory>
 #include <iomanip>
-#include <codecvt>
 
 #include "keyman_core.h"
 #include "jsonpp.hpp"
@@ -22,6 +21,7 @@
 #include "state.hpp"
 #include "vkey_to_contextreset.hpp"
 #include "kmx_file.h"
+#include "utfcodec.hpp"
 
 using namespace km::core;
 
@@ -357,7 +357,7 @@ km_core_cu * km_core_state_context_debug(
 
   km_core_context_items_dispose(context_items);
 
-  std::u16string s = std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t>{}.from_bytes(buffer.str());
+  std::u16string s = convert<char, char16_t>(buffer.str());
 
   km_core_cu* result = new km_core_cu[s.size() + 1];
   s.copy(result, s.size());

core/src/kmx/kmx_xstring.cpp

@@ -4,7 +4,6 @@
 */
 #include <vector>
 #include <iterator>
-#include <codecvt>
 #include <locale>
 #include "kmx_processevent.h"
 #include "utfcodec.hpp"

core/tests/unit/ldml/ldml_test_source.cpp

@@ -8,7 +8,6 @@
 #include <sstream>
 #include <string>
 #include <type_traits>
-#include <codecvt>
 
 #if 0
 // TODO-LDML If we need to avoid exceptions in JSON
@@ -200,7 +199,7 @@ LdmlTestSource::parse_source_string(std::string const &s) {
 std::u16string
 LdmlTestSource::parse_u8_source_string(std::string const &u8s) {
   // convert from utf-8 to utf-16 first
-  std::u16string s = std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t>{}.from_bytes(u8s);
+  std::u16string s = convert<char, char16_t>(u8s);
   std::u16string t;
   for (auto p = s.begin(); p != s.end(); p++) {
     if (*p == '\\') {
@@ -219,7 +218,7 @@ LdmlTestSource::parse_u8_source_string(std::string const &u8s) {
         size_t n;
         std::u16string s1 = s.substr(p - s.begin(), 8);
         // TODO-LDML: convert back first?
-        std::string s1b = std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t>{}.to_bytes(s1);
+        std::string s1b = convert<char16_t, char>(s1);
         v              = std::stoul(s1b, &n, 16);
         // Allow deadkey_number (U+0001) characters and onward
         assert(v >= 0x0001 && v <= 0x10FFFF);

docs/build/old/core-desktop-notes.md

@@ -6,7 +6,7 @@ WARNING: these are old configuration notes. See [index.md](../index.md) for curr
 - Python 3
 - Meson build system 0.45+ (0.56+ for WASM)
 - ninja 1.8+
-- C++14 or later compiler (VC++ 2019 or later for Windows).
+- C++17 or later compiler (VC++ 2019 or later for Windows).
 - lib std::fs
 - kmc (for tests) -- must be added to path