com

com.cpp

/* $ clang++ -o # @ -O2 -Wall
 *
 * compile anything
 * original version by Tom Duff: http://www.iq0.com/duffgram/com.html
 * here's my own version, with the purpose to learn exec() syscall.
 *
 *                                                          - 44
 *                                                         2021.11.24
 */

// @TODO: don't force C-style comments at start

#include <fcntl.h>
#include <unistd.h>

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void no_compile_command() {
  printf("no compile command found.\n");
  printf("add your compile command to the first line of your program like:\n");
  printf("    // $ clang @ -o #\n");
  printf("where:\n");
  printf("    $ is the start of the command\n");
  printf("    @ is the source filename\n");
  printf("    # is the source filename without extension\n");
  exit(1);
}

void help(const char *prog) {
  printf("usage: %s [-qg] <source> [more arguments]...\n", prog);
  printf("    -q: don't echo the compile command\n");
  printf("    -g: generate compile_commands.json\n");
}

int main(int argc, char *argv[]) {
  if (argc < 2) {
    help(argv[0]);
    exit(1);
  }

  int arg_index = 1;
  bool quiet_mode = false;
  bool generate_compile_commands_json = false;

  while (argv[arg_index][0] == '-') {
    if (argv[arg_index][0] == '-') {
      if (argv[arg_index][1] == 'q') {
        quiet_mode = true;
      } else if (argv[arg_index][1] == 'g') {
        generate_compile_commands_json = true;
      } else {
        help(argv[0]);
        exit(1);
      }
    }
    arg_index++;
  }

  const char *filename = argv[arg_index];

  int source_fd = open(filename, O_RDONLY);
  if (source_fd == -1) {
    printf("unable to open file: %s\n", argv[arg_index]);
    exit(1);
  }

  // get the first line
  char buffer[8096];
  char *sp = buffer;
  int rc;
  while ((rc = read(source_fd, sp, 1) != 0)) {

    if (rc == -1) {
      printf("read error\n");
      exit(1);
    }

    if (*sp == '\0') {
      no_compile_command();
    } else if (*sp == '\n') {
      *sp = '\0';
      break;
    } else if (*sp == '@') {
      strcpy(sp, argv[arg_index]);
      sp += strlen(sp);
    } else if (*sp == '#') {
      strcpy(sp, argv[arg_index]);
      for (int i = strlen(sp); i >= 0; i--) {
        if (sp[i] == '.') {
          sp[i] = '\0';
          sp += i;
          break;
        }
        if (i == 0) {
          printf("file has no extension.\n");
          exit(1);
        }
      }
    } else {
      sp++;
    }
  }

  close(source_fd);

  arg_index++;
  // concat additional arguments to buffer
  for (int i = arg_index; i < argc; i++) {
    sp += sprintf(sp, " %s", argv[i]);
  }

  // find the command in the first line
  // by skipping // or /*, plus a $,
  // which is the start of the command.

  sp = buffer;
  while (isspace(*sp))
    sp++;
  if (sp[0] != '/' || (sp[1] != '*' && sp[1] != '/')) {
    no_compile_command();
  }
  sp += 2; // skip comment mark

  while (isspace(*sp))
    sp++;
  if (sp[0] != '$') {
    no_compile_command();
  }
  sp += 1; // skip $

  while (isspace(*sp))
    sp++;

  char *command = sp;

  if (!quiet_mode) {
    printf("%s\n", command);
  }

  if (generate_compile_commands_json) {
    int cc = open("compile_commands.json", O_WRONLY | O_CREAT | O_TRUNC, 0655);
    if (cc == -1) {
      printf("unable to open file: compile_commands.json\n");
      exit(1);
    }

    char *abs_path = realpath(filename, NULL);

    if (!abs_path) {
      printf("realpath: error\n");
      exit(1);
    }

    char buf[8096];
    sprintf(buf,
            "[\n"
            "  {\n"
            "    \"command\": \"%s\",\n"
            "    \"directory\": \".\",\n"
            "    \"file\": \"%s\"\n"
            "  }\n"
            "]\n",
            command, abs_path);

    if (write(cc, buf, strlen(buf)) == -1) {
      printf("unable to write file: compile_commands.json\n");
      exit(1);
    }
    close(cc);
    free(abs_path);
  }

  if (execl("/bin/sh", "sh", "-c", command, NULL) == -1) {
    printf("exec error\n");
    exit(1);
  }

  return 0;
}