Remove custom permission error code and restore path in read error

[rwstauner]

The existing error message says

bootsnap doesn't have permission to write cache entries in '#{cache_path}'
(or, less likely, doesn't have permission to read '#{path}')"

but at this point i think the error will never be about the cache and only for the original file.

We stopped reporting write errors in
d878622
and read errors in
503e9d5

In that case it seems like we may as well remove the wrapper class and let the original error bubble up...
but when I did that the exception message was the code "bs_fetch:open_current_file:open" rather than mentioning what file path failed to be read.

My C is incredibly rusty; I don't know if this is a good idea.

What do you think? Do we want to do it this way?
Are there other places we should replace the "bs:*" code with the file path (like the fstat that follows?)

Another option would be to keep the ruby method and just simplify the message
(in which case the C code wouldn't have to change).

[casperisfine]

So open_current_file is only called from bs_fetch, and path here is RSTRING_PTR of the path_v bs_fetch received.

If we return fd <0, bs_fetch jumps to the fail_errno label, so we're not actually giving more information to the caller here, since it already have path_v on its stack.

If we wish to augment or change the error message, we can directly do it there.

[rwstauner]

Thanks, I like that idea.

In bs_fetch we will goto fail_errno in several cases:

• an error opening (or fstat-ing) the file in open_current_file (the most likely case to be useful to the user)
  

  bootsnap/ext/bootsnap/bootsnap.c

  Line 688 in 34dba5c

  if (current_fd < 0) goto fail_errno;

• after open_cache_file... this returns CACHE_MISS for reading the cache file,
  but will forward the errno from a read in bs_read_key
  

  bootsnap/ext/bootsnap/bootsnap.c

  Line 698 in 34dba5c

  goto fail_errno;

• after bs_read_contents calls read on the fd of the current file
  

  bootsnap/ext/bootsnap/bootsnap.c

  Line 720 in 34dba5c

  if ((input_data = bs_read_contents(current_fd, current_key.size, &errno_provenance)) == Qfalse) goto fail_errno;

  
  and
  

  bootsnap/ext/bootsnap/bootsnap.c

  Line 733 in 34dba5c

  if ((input_data = bs_read_contents(current_fd, current_key.size, &errno_provenance)) == Qfalse) goto fail_errno;

• after fetch_cached_data if it fails to read the rest of the cache file (after the key has been read)
  

  bootsnap/ext/bootsnap/bootsnap.c

  Line 725 in 34dba5c

  else if (res == ERROR_WITH_ERRNO) goto fail_errno;

• after unlink-ing the cache file
  

  bootsnap/ext/bootsnap/bootsnap.c

  Line 770 in 34dba5c

  goto fail_errno;

I updated the code to set the message to the file the operation was on, but I may have gone a little overboard. 😅

[casperisfine]

I like it, thanks.