[ruby-core:106194] [Ruby master Bug#18355] require("pathname") within rack application chnages behaviors of Pathname methods, such as absolute?(), when there are two versions of 'pathname' gem installed.

Issue #18355 has been reported by ume-san (Toshi Umehara).

----------------------------------------
Bug #18355: require("pathname") within rack application chnages behaviors of Pathname methods, such as absolute?(), when there are two versions of 'pathname' gem installed.
https://bugs.ruby-lang.org/issues/18355

* Author: ume-san (Toshi Umehara)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
## Environment

Ruby 3.0.2 is installed on Fedora 34 from source.
'gem update' is conducted, and there are two versions of 'pathname' gems (0.2.0, default: 0.1.0) installed as follows.

```
> uname -a
Linux localhost.localdomain 5.14.18-200.fc34.x86_64 #1 SMP Fri Nov 12 16:48:10 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

> ruby -v
ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]

> gem update --system
> gem update

> gem list
...
pathname (0.2.0, default: 0.1.0)
...

```

## Code

The following files, Gemfile and config.ru, are placed in the same directory.

```
# Gemfile

source 'https://rubygems.org/'
gem 'rack'
gem 'webrick'
```

```
# config.ru

class Application
  def call(env)
    status  = 200
    headers = { "Content-Type" => "text/html" }
    path = Dir.pwd()

    pathname1 = Pathname.new(path)

    require("pathname")
    pathname2 = Pathname.new(path)

    body    = ["#{pathname1.absolute?} #{pathname2.absolute?}"]

    [status, headers, body]
  end
end

run Application.new
```

## Command

Web server starts using the following commands.

```
bundle config set --local path 'vendor/bundle'
bundle install
bundle exec rackup -s webrick
```

* Output on the console

```
[2021-11-21 09:44:13] INFO  WEBrick 1.7.0
[2021-11-21 09:44:13] INFO  ruby 3.0.2 (2021-07-07) [x86_64-linux]
[2021-11-21 09:44:13] INFO  WEBrick::HTTPServer#start: pid=2770 port=9292
```


## Expected Result

Accessing localhost:9292 using a web browser , 'true true' is an expected result on the browser, because pathname1 and pathanme2 are generated from the same absolute path in the above code.

```
true true
```


## Actual Result

Accessing localhost:9292 shows the following messages on the browser and the console. After 'require("pathname")', Pathname.absolute?() retuns false, even if represents an absolute path.

* On the browser

```
true false
```

* On the console

```
/home/toshihiro/Ruby3/lib/ruby/3.0.0/pathname.rb:20: warning: already initialized constant Pathname::TO_PATH
/home/toshihiro/Ruby3/lib/ruby/gems/3.0.0/gems/pathname-0.2.0/lib/pathname.rb:20: warning: previous definition of TO_PATH was here
/home/toshihiro/Ruby3/lib/ruby/3.0.0/pathname.rb:22: warning: already initialized constant Pathname::SAME_PATHS
/home/toshihiro/Ruby3/lib/ruby/gems/3.0.0/gems/pathname-0.2.0/lib/pathname.rb:22: warning: previous definition of SAME_PATHS was here
/home/toshihiro/Ruby3/lib/ruby/3.0.0/pathname.rb:34: warning: already initialized constant Pathname::SEPARATOR_LIST
/home/toshihiro/Ruby3/lib/ruby/gems/3.0.0/gems/pathname-0.2.0/lib/pathname.rb:34: warning: previous definition of SEPARATOR_LIST was here
/home/toshihiro/Ruby3/lib/ruby/3.0.0/pathname.rb:35: warning: already initialized constant Pathname::SEPARATOR_PAT
/home/toshihiro/Ruby3/lib/ruby/gems/3.0.0/gems/pathname-0.2.0/lib/pathname.rb:35: warning: previous definition of SEPARATOR_PAT was here
/home/toshihiro/Ruby3/lib/ruby/3.0.0/pathname.rb:41: warning: already initialized constant Pathname::ABSOLUTE_PATH
/home/toshihiro/Ruby3/lib/ruby/gems/3.0.0/gems/pathname-0.2.0/lib/pathname.rb:41: warning: previous definition of ABSOLUTE_PATH was here
127.0.0.1 - - [21/Nov/2021:09:44:20 +0900] "GET / HTTP/1.1" 200 10 0.0339
```

## Segmentation fault

Moreover, press Ctrl-c to stop the Rack application, the application causes a segmentation fault.

The segmentation fault message is attached.


## Notes

Uninstalling version 0.2.0 of pathname gem solves the problem above. Therefore, I guess having two versions of pathname gems causes this behavior.

```
gem uninstall pathname --version=0.2.0
```

* Start the Rack application again

```
bundle exec rackup -s webrick
```

* Output on the browser

The expected output is obtained on the browser, without warning messages on the console.

```
true true
```

---Files--------------------------------
segmentation_fault.txt (51.1 KB)


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