[ruby-core:75450] [Ruby trunk Bug#12359] Named captures "conflict" warning is unnecessary and limits uses of named captures

Issue #12359 has been updated by Charles Nutter.


Related Ruby issue: https://bugs.ruby-lang.org/issues/9623

I think the warning needs to be softened to allow repeat use in literal regexp at the very least.


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Bug #12359: Named captures "conflict" warning is unnecessary and limits uses of named captures
https://bugs.ruby-lang.org/issues/12359#change-58569

* Author: Charles Nutter
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin14]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
There's currently a warning whenever a named capture in a regular expression has the same name as an already-declared local variable:

```
$ ruby23 -v -e 'x = 1; /(?<x>foo)/ =~ "foo"'
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin14]
-e:1: warning: named capture conflicts a local variable - x
```

It also warns if you have two expressions using the same named capture:

```
$ ruby23 -v -e '/(?<x>foo)/ =~ "foo"; /(?<x>foo)/ =~ "foo"'
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin14]
-e:1: warning: named capture conflicts a local variable - x
```

I do not believe either of these warnings are useful, since the only option for fixing them is to use a new variable name for every named capture.

I have a few more reasons, as well:

* Using the same named capture on both the "then" and "else" branches of an "if" statement will produce a warning. Changing one of the names requires additional work to join the to branches back together (since now there's no single variable resulting from them).
* It is not possible to initialize a variable with the same name as a named capture.
* The pattern that results from this warning is renaming a capture something like "name2" and then having "name = name2" after the match. Ugly.

Risks of removing the warning:

* When a named capture writes to an already-declared variable, that may surprise a user.

I think this risk is very low, especially since you'd have to turn on verbose mode to even see the warning.



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