Try to convert OS::execute() output to Unicode on Windows

(cherry picked from commit a71e8081124eaf4eac6059bfeb3550a400bc2002)

platform/windows/os_windows.cpp

@@ -2803,6 +2803,31 @@ String OS_Windows::_quote_command_line_argument(const String &p_text) const {
 	return p_text;
 }
 
+static void _append_to_pipe(char *p_bytes, int p_size, String *r_pipe, Mutex *p_pipe_mutex) {
+	// Try to convert from default ANSI code page to Unicode.
+	LocalVector<wchar_t> wchars;
+	int total_wchars = MultiByteToWideChar(CP_ACP, 0, p_bytes, p_size, nullptr, 0);
+	if (total_wchars > 0) {
+		wchars.resize(total_wchars);
+		if (MultiByteToWideChar(CP_ACP, 0, p_bytes, p_size, wchars.ptr(), total_wchars) == 0) {
+			wchars.clear();
+		}
+	}
+
+	if (p_pipe_mutex) {
+		p_pipe_mutex->lock();
+	}
+	if (wchars.empty()) {
+		// Let's hope it's compatible with UTF-8.
+		(*r_pipe) += String::utf8(p_bytes, p_size);
+	} else {
+		(*r_pipe) += String(wchars.ptr(), total_wchars);
+	}
+	if (p_pipe_mutex) {
+		p_pipe_mutex->unlock();
+	}
+}
+
 Error OS_Windows::execute(const String &p_path, const List<String> &p_arguments, bool p_blocking, ProcessID *r_child_id, String *r_pipe, int *r_exitcode, bool read_stderr, Mutex *p_pipe_mutex, bool p_open_console) {
 	String path = p_path.replace("/", "\\");
 
@@ -2861,21 +2886,44 @@ Error OS_Windows::execute(const String &p_path, const List<String> &p_arguments,
 	if (p_blocking) {
 		if (r_pipe) {
 			CloseHandle(pipe[1]); // Close pipe write handle (only child process is writing).
-			char buf[4096];
+
+			LocalVector<char> bytes;
+			int bytes_in_buffer = 0;
+
+			const int CHUNK_SIZE = 4096;
 			DWORD read = 0;
 			for (;;) { // Read StdOut and StdErr from pipe.
-				bool success = ReadFile(pipe[0], buf, 4096, &read, NULL);
+				bytes.resize(bytes_in_buffer + CHUNK_SIZE);
+				const bool success = ReadFile(pipe[0], bytes.ptr() + bytes_in_buffer, CHUNK_SIZE, &read, NULL);
 				if (!success || read == 0) {
 					break;
 				}
-				if (p_pipe_mutex) {
-					p_pipe_mutex->lock();
+				// Assume that all possible encodings are ASCII-compatible.
+				// Break at newline to allow receiving long output in portions.
+				int newline_index = -1;
+				for (int i = read - 1; i >= 0; i--) {
+					if (bytes[bytes_in_buffer + i] == '\n') {
+						newline_index = i;
+						break;
+					}
 				}
-				(*r_pipe) += String::utf8(buf, read);
-				if (p_pipe_mutex) {
-					p_pipe_mutex->unlock();
+
+				if (newline_index == -1) {
+					bytes_in_buffer += read;
+					continue;
 				}
-			};
+
+				const int bytes_to_convert = bytes_in_buffer + (newline_index + 1);
+				_append_to_pipe(bytes.ptr(), bytes_to_convert, r_pipe, p_pipe_mutex);
+
+				bytes_in_buffer = read - (newline_index + 1);
+				memmove(bytes.ptr(), bytes.ptr() + bytes_to_convert, bytes_in_buffer);
+			}
+
+			if (bytes_in_buffer > 0) {
+				_append_to_pipe(bytes.ptr(), bytes_in_buffer, r_pipe, p_pipe_mutex);
+			}
+
 			CloseHandle(pipe[0]); // Close pipe read handle.
 		} else {
 			WaitForSingleObject(pi.pi.hProcess, INFINITE);
@@ -2897,7 +2945,7 @@ Error OS_Windows::execute(const String &p_path, const List<String> &p_arguments,
 		process_map->insert(pid, pi);
 	}
 	return OK;
-};
+}
 
 Error OS_Windows::kill(const ProcessID &p_pid) {
 	ERR_FAIL_COND_V(!process_map->has(p_pid), FAILED);