[ruby-core:82931] [Ruby trunk Feature#13613] Prefer that require/require_relative/load to tell us permission error if the target file is unreadable

Issue #13613 has been updated by sonots (Naotoshi Seo).


I tried to write a patch which just adding `strerror(errno)` to error message. 
https://github.com/sonots/ruby/commit/4af8960b65aec1c4a82d81431ed812bcebcdf7f8

But, I noticed that it was very fragile.

```
$:.replace([IO::NULL])
require 'foo'
```

This tells `cannot load such file -- Not a directory -- foo (LoadError)` rather than `cannot load such file -- No such file or directory -- foo (LoadError)`.
The error message depends on orders of calling syscalls internally, which is very fragile.


----------------------------------------
Feature #13613: Prefer that require/require_relative/load to tell us permission error if the target file is unreadable
https://bugs.ruby-lang.org/issues/13613#change-66832

* Author: sonots (Naotoshi Seo)
* Status: Feedback
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
### Background

https://github.com/google/google-api-ruby-client/issues/205

We've ever met a situation that read-permissions of files in released google-api-client gem were lost as:

```
$ ls -l ~/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/google-api-client-0.8.3/lib/google
-rw-r----- 1 sonots sonots 27249  March 24 18:32 2015 api_client.rb
```

The error message was

```
in `require': cannot load such file -- api_client.rb (LoadError)
```

At that time, it took 30 minutes for me to find the reason why we get LoadError with the gem because the file exists.
I looked the source codes load.c, and finally I found the reason as it is because of permission with my intuition.

### What I Want

If `require` tells us PermissionError in addition to LoadError, I could figure out the reason soon.
I think the additional information is helpful for finding such issues.





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