[ruby-core:111037] [Ruby master Misc#19155] documentation of Pathname#join with absolute path

["sawa (Tsuyoshi Sawada)" <noreply@ruby-lang.org>]

Issue #19155 has been updated by sawa (Tsuyoshi Sawada).


There is a description.

The doc https://docs.ruby-lang.org/ja/latest/class/Pathname.html#I_JOIN says:

```ruby
path0 = Pathname("/usr")                # Pathname:/usr
path0 = path0.join("bin/ruby")          # Pathname:/usr/bin/ruby
   # 上記の path0 の処理は下記の path1 と同様のパスになります
path1 = Pathname("/usr") + "bin/ruby"   # Pathname:/usr/bin/ruby
path0 == path1                          #=> true
```

where "上記の `path0` の処理は下記の `path1` と同様のパスになります" translates to English as "the path of `path0` above is handled on a par with `path1` below", which means that `join` follows the specification of `+`. And here https://docs.ruby-lang.org/ja/latest/class/Pathname.html#I_--2B it says:

> self + other -> Pathname[permalink][rdoc][edit]
> self / other -> Pathname
> パス名を連結します。つまり、other を self からの相対パスとした新しい Pathname オブジェクトを生成して返します。
> other が絶対パスなら単に other と同じ内容の Pathname オブジェクトが返されます。

where "`other` が絶対パスなら単に `other` と同じ内容の `Pathname` オブジェクトが返されます。" translates to English as "if `other` is an absolute path, then simply a `Pathname` object with the same content as `other` would be returned".

----------------------------------------
Misc #19155: documentation of Pathname#join with absolute path
https://bugs.ruby-lang.org/issues/19155#change-100290

* Author: colorbox (box color)
* Status: Open
* Priority: Normal
----------------------------------------
Pathname#join ignores previous directory name before absolute path

Is this intentional?

```irb
irb(main):002:0> require 'pathname'
=> true
irb(main):003:0> Pathname('/foo').join('bar', 'baz')
=> #<Pathname:/foo/bar/baz>
irb(main):004:0> Pathname('/foo').join('bar', '/baz')
=> #<Pathname:/baz>
irb(main):005:0> 

➜✗ ruby -v
ruby 3.0.4p208 (2022-04-12 revision 3fa771dded) [x86_64-darwin19]
```

I found that this behavior is intentional from test code but I cannot found reason.
https://github.com/ruby/pathname/blob/master/test/pathname/test_pathname.rb#L248-L261

There was no description of this behavior in the documentation.




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