[ruby-core:107514] [Ruby master Feature#18576] Rename `ASCII-8BIT` encoding to `BINARY`

["byroot (Jean Boussier)" <noreply@ruby-lang.org>]

Issue #18576 has been reported by byroot (Jean Boussier).

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Feature #18576: Rename `ASCII-8BIT` encoding to `BINARY`
https://bugs.ruby-lang.org/issues/18576

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
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### Context

I'm now used to it, but something that confused me for years was errors such as:

```ruby
>> "fée" + "\xFF".b
(irb):3:in `+': incompatible character encodings: UTF-8 and ASCII-8BIT (Encoding::CompatibilityError)
```

When you aren't that familiar with Ruby, it's really not evident that `ASCII-8BIT` basically means "no encoding" or "binary".

And even when you know it, if you don't read carefully it's very easily confused with `US-ASCII`.

The `Encoding::BINARY` alias is much more telling IMHO.

### Proposal

Since `Encoding::ASCII_8BIT` has been aliased as `Encoding::BINARY` for years, I think renaming it to `BINARY` and then making asking `ASCII_8BIT` the alias would significantly improve usability without backward compatibility concerns.

The only concern I could see would be the consistency with a handful of C API functions:

  - `rb_encoding *rb_ascii8bit_encoding(void)`
  - `int rb_ascii8bit_encindex(void)`
  - `VALUE rb_io_ascii8bit_binmode(VALUE io)`

But that's for much more advanced users, so I don't think it's much of a concern.




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