[ruby-core:117437] [Ruby master Misc#20406] Question about Regexp encoding negotiation

Issue #20406 has been updated by duerst (Martin D=FCrst).


This is a more general comment, but my impression is that the encoding flag=
s on regular expressions may be outdated. They exist since before Ruby intr=
oduced encoding information for Strings,... in Ruby 1.9. It may be time now=
 to look into how/when they can be deprecated.

----------------------------------------
Misc #20406: Question about Regexp encoding negotiation
https://bugs.ruby-lang.org/issues/20406#change-107813

* Author: andrykonchin (Andrew Konchin)
* Status: Open
----------------------------------------
I am wondering what are the rules to calculate Regexp literal encoding in c=
ase an encoding modifier is specified.


>From the documentstion:

> By default, a regexp with only US-ASCII characters has US-ASCII encoding:
> ...
> A regular expression containing non-US-ASCII characters is assumed to use=
 the source encoding. This can be overridden with one of the following modi=
fiers.
> //n ...
> //u ...
> //e ...
> //s ...

Looking at the following examples I would assume that these rules are follo=
wed except one case:

```ruby
 p /\xc2\xa1/e     .encoding # EUC-JP
 p /#{ }\xc2\xa1/e .encoding # EUC-JP

 p /a/e            .encoding # EUC-JP
 p /a #{} a/e      .encoding # EUC-JP
 p /#{} a/e        .encoding # US-ASCII
```

The last Regexp `/#{} a/e` is supposed to have `EUC-JP` encoding but has `U=
S-ASCII`. So I am wondering what rule is applied in this case.



--=20
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