Issue #13798 has been reported by shyouhei (Shyouhei Urabe).

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Bug #13798: Strange "invalid subexp call" warning happens inside of comment
https://bugs.ruby-lang.org/issues/13798

* Author: shyouhei (Shyouhei Urabe)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.5.0dev (2017-08-10 trunk 59556) [x86_64-darwin15]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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Attached script renders "invalid subexp call" warning.

```
zsh % ruby warn.rb
warn.rb:4: warning: invalid subexp call
```

This is strange in several ways:

 - The warning is triggered by Regexp#to_s, not by the compilation.
 - There is no such thing like a subexp call in the regular expression.

---Files--------------------------------
warn.rb (82 Bytes)


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