From: janosch-x <noreply@...>
Date: 2022-05-23T10:17:54+00:00
Subject: [ruby-core:108656] [Ruby master Feature#18788] Support passing Regexp options as String to Regexp.new

Issue #18788 has been updated by janosch-x (Janosch M��ller).


@nobu

Thank you for the explanation regarding symbols!

> we'll need migration period to warn anything other than inter and valid string

I think the optional third argument should be also deprecated as described in #18797. Otherwise we might still want to allow `nil` as "stopgap" value for the second argument.

> Regexp.new(code, eval("//#{options}").options)

This feels too unsafe for some of the cases mentioned above.

> Regexp.new("(?#{options}:#{code})")

This is clever and will work for most of the use cases mentioned above. Just a few minor downsides:

1. The group options syntax isn't so well-known and universally understood.
2. A few use cases might need to preserve notation (e.g. codemod).
3. The result may become verbose in case of recursion or nesting of Regexps.

----------------------------------------
Feature #18788: Support passing Regexp options as String to Regexp.new
https://bugs.ruby-lang.org/issues/18788#change-97699

* Author: janosch-x (Janosch M��ller)
* Status: Open
* Priority: Normal
----------------------------------------
## Current situation

`Regexp.new` takes an integer as second argument which needs to be ORed together from multiple constants:

```
Regexp.new('foo', Regexp::IGNORECASE | Regexp::MULTILINE | Regexp::EXTENDED) # => /foo/imx
```

Any other non-nil value is treated as `i` flag:

```
Regexp.new('foo', Object.new) # => /foo/i
```

## Suggestion

`Regexp.new` should support passing the regexp flags not only as an Integer, but also as a String or Symbol, like so:

```
Regexp.new('foo', 'i')   # => /foo/i
Regexp.new('foo', :i)    # => /foo/i
Regexp.new('foo', 'imx') # => /foo/imx
Regexp.new('foo', :imx)  # => /foo/imx

# edge cases
Regexp.new('foo', 'iii') # => /foo/i
Regexp.new('foo', :iii)  # => /foo/i
Regexp.new('foo', '')    # => /foo/
Regexp.new('foo', :'')   # => /foo/

# unsupported flags could be ignored -
# or raise an ArgumentError to reveal changed behavior?
Regexp.new('foo', 'jmq') # => /foo/m
Regexp.new('foo', :jmq)  # => /foo/m
Regexp.new('foo', '-m')  # => /foo/m
Regexp.new('foo', :'-m') # => /foo/m
```

## Reasons

1. The constants are a bit cumbersome to use, particularly when building the regexp from variable data:

```
def make_regexp(regexp_body, opt_string)
  opt_int = 0
  opt_int |= Regexp::IGNORECASE if opt_string.include?('i')
  opt_int |= Regexp::MULTILINE  if opt_string.include?('m')
  opt_int |= Regexp::EXTENDED   if opt_string.include?('x')

  Regexp.new(regexp_body, opt_int)
end
```

2. Passing a String or Symbol is already silently accepted, and people might get the wrong impression that it works:

```
Regexp.new('foo', 'i') # => /foo/i
Regexp.new('foo', :i)  # => /foo/i
```

... but it doesn't really work:

```
Regexp.new('foo', 'x') # => /foo/i
Regexp.new('foo', :x)  # => /foo/i
```

## Backwards compatibility

This change would not be fully backwards compatible.

Code that relies on the second argument being either a String/Symbol or nil to decide whether the Regexp should be case insensitive would break (unless the String or Symbol contains "i").

I can't come up with a scenario where one would write such code, though - except maybe code golfing?




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