cpprepl.cpp

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#include <dlfcn.h>

#include <readline/readline.h>
#include <readline/history.h>
#include <cstdlib>

// returns stdout and stderr combined
std::string run(std::string exe, std::vector<std::string> args, std::string stdin_s, int &ec) {
	int stdin_pipe[2];
	int stdout_pipe[2];
	pipe(stdin_pipe);
	pipe(stdout_pipe);

	pid_t child = fork();

	std::string stdout_s;

	if (!child) {
		dup2(stdin_pipe[0], STDIN_FILENO);
		dup2(stdout_pipe[1], STDOUT_FILENO);
		dup2(stdout_pipe[1], STDERR_FILENO);

		std::vector<char *> arg_ptrs;
		std::transform(args.begin(), args.end(), std::back_inserter(arg_ptrs), [] (auto &v) { return v.data(); });
		arg_ptrs.push_back(nullptr);

		close(stdin_pipe[0]);
		close(stdin_pipe[1]);
		close(stdout_pipe[0]);
		close(stdout_pipe[1]);
		execv(exe.data(), arg_ptrs.data());
	} else {
		close(stdout_pipe[1]);
		close(stdin_pipe[0]);

		write(stdin_pipe[1], stdin_s.data(), stdin_s.size());
		close(stdin_pipe[1]);

		int wstatus;
		wait(&wstatus);

		ec = WIFEXITED(wstatus) ? WEXITSTATUS(wstatus) : -1;

		ssize_t n;
		char buf[4096];
		while ((n = read(stdout_pipe[0], buf, 4096)) > 0) {
			stdout_s += std::string_view{buf, size_t(n)};
		}

		close(stdout_pipe[0]);
	}

	return stdout_s;
}

int main() {
	using_history();

	while (true) {
		auto input = readline(">>> ");
		if (!input) // EOF
			break;

		add_history(input);

		std::string line{input};
		std::free(input);

		std::string code = "#include <bits/stdc++.h>\n"
			+ ("[[gnu::constructor]] void dont_mind_me_great_code_here___() {"
			+ line + "}");

		int ec;
		auto out = run("/usr/bin/clang++",
				{"clang++", "-std=c++20", "-shared",
				"-fuse-ld=lld", "-x", "c++", "-",
				"-o", "/dev/stdout"}, code, ec);

		if (ec != 0) {
			std::cout << out << std::flush;
		} else {
			int fd = memfd_create("so", MFD_CLOEXEC);
			write(fd, out.data(), out.size());

			char buf[512];
			snprintf(buf, 512, "/proc/self/fd/%d", fd);

			void *dl = dlopen(buf, RTLD_NOW);
			dlclose(dl);
			close(fd);
			std::cout << std::endl;
		}

	}
}