[lit] Internal shell will hang when fork outlives parent with a file descriptor

[boomanaiden154]

If we take the minimal following c program:

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <time.h>

int main() {
    int test = fork();
    if (test == 0) {
        printf("Exiting parent\n");
        return 0;
    } else if (test > 0) {
        struct timespec test5 = {1, 0};
        int fd = open("/tmp/test10", O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
        nanosleep(&test5, NULL);
        write(fd, "test", 4);
        write(fd, "test", 4);
        close(fd);
    }
    printf("Exiting fork\n");
    exit(0);
    return 0;
}

and try to execute it with lit using the internal shell with a test file like the following:

// RUN: %clang %S/test.c -o %t.exe
// RUN: %t.exe

lit will end up hanging in a Popen.communicate() call for unknown reasons. A workaround for now is to just invoke the test with bash and have a wait call:

// RUN: %clang %S/test.c -o %t.exe
// RUN: bash -c "%t.exe; wait"