Backport: Implement WStringFromUTF8 to simplify code that creates wstring objects for

regular expressions and calling the Win32 API.

Backport of changeset 7325:6148329fb2f3, but replaced std::string_view usage
with const char* and size_t components. Also used #ifdef instead of C++17
`if constexpr` at suggestion of Neil.

1 files changed, 25 insertions, 0 deletions

diff --git a/src/UniConversion.cxx b/src/UniConversion.cxx
index 6cd6a8ba9..8cbb3cdd2 100644
--- a/src/UniConversion.cxx
+++ b/src/UniConversion.cxx
@@ -162,6 +162,17 @@ size_t UTF16FromUTF8(const char *s, size_t len, wchar_t *tbuf, size_t tlen) {
 	return ui;
 }
 
+size_t UTF32Length(const char *s, size_t len) noexcept {
+	size_t ulen = 0;
+	for (size_t i = 0; i < len;) {
+		const unsigned char ch = s[i];
+		const unsigned int byteCount = UTF8BytesOfLead[ch];
+		i += byteCount;
+		ulen++;
+	}
+	return ulen;
+}
+
 size_t UTF32FromUTF8(const char *s, size_t len, unsigned int *tbuf, size_t tlen) {
 	size_t ui = 0;
 	for (size_t i = 0; i < len;) {
@@ -215,6 +226,20 @@ size_t UTF32FromUTF8(const char *s, size_t len, unsigned int *tbuf, size_t tlen)
 	return ui;
 }
 
+std::wstring WStringFromUTF8(const char *s, size_t len) {
+#ifdef _WIN32
+		const size_t len16 = UTF16Length(s, len);
+		std::wstring ws(len16, 0);
+		UTF16FromUTF8(s, len, &ws[0], len16);
+		return ws;
+#else
+		const size_t len32 = UTF32Length(s, len);
+		std::wstring ws(len32, 0);
+		UTF32FromUTF8(s, len, reinterpret_cast<unsigned int *>(&ws[0]), len32);
+		return ws;
+#endif
+}
+
 unsigned int UTF16FromUTF32Character(unsigned int val, wchar_t *tbuf) noexcept {
 	if (val < SUPPLEMENTAL_PLANE_FIRST) {
 		tbuf[0] = static_cast<wchar_t>(val);