From: "Dan0042 (Daniel DeLorme) via ruby-core" <ruby-core@...>
Date: 2025-06-01T13:02:13+00:00
Subject: [ruby-core:122360] [Ruby Bug#21391] Inconsistent trailing slash behavior of File.join and Pathname#join with empty strings

Issue #21391 has been updated by Dan0042 (Daniel DeLorme).


It's not the only inconsistent behavior:
```ruby
File.join("/usr","/var")               #=> "/usr/var"
Pathname.new("/usr").join("/var").to_s #=> "/var"

File.join("/usr","../var")               #=> "/usr/../var"
Pathname.new("/usr").join("../var").to_s #=> "/var"

File.join("/usr","/../var")               #=> "/usr/../var"
Pathname.new("/usr").join("/../var").to_s #=> "/../var"
```

`File.join` simply joins two strings together with a separator, whereas `Pathname#join` is a logical operation on two paths. It's normal for there to be differences.

That being said, I feel that `Pathname.new('/usr').join('')` is a nonsensical operation. It seems to result in a no-op, but it might be better to warn or raise an error.

----------------------------------------
Bug #21391: Inconsistent trailing slash behavior of File.join and Pathname#join with empty strings
https://bugs.ruby-lang.org/issues/21391#change-113503

* Author: lovro-bikic (Lovro Biki��)
* Status: Open
* ruby -v: ruby 3.4.4 (2025-05-14 revision a38531fd3f) +PRISM [x86_64-darwin23]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
```ruby
File.join('/usr', '')
# => "/usr/"

Pathname.new('/usr').join('').to_s
# => "/usr" # no trailing slash

File.join('/usr', ' ')
# => "/usr/ "

Pathname.new('/usr').join(' ').to_s
# => "/usr/ "
```

`File.join` with an empty string adds a trailing slash, `Pathname#join` doesn't.
When `Pathname#join` argument is a string with empty whitespace, a trailing slash is added (plus whitespace).

I think it's a common use-case to append a trailing slash to `Pathname`, and currently you have to resort to other methods such as string interpolation (e.g. in Rails, `"#{Rails.root}/"`) or `File.join` (e.g. `File.join(Rails.root, '')`).

In other popular languages, both approaches have been taken:
- [`os.path.join` in Python](https://docs.python.org/3.12/library/os.path.html#os.path.join) adds a trailing slash:
```python
import os
os.path.join('/usr', '')
# '/usr/'
```
- [Path.join in Rust](https://doc.rust-lang.org/std/path/struct.Path.html#method.join) adds a trailing slash:
```rust
use std::path::{Path};

fn main() {
    println!("{}", Path::new("/usr").join("").display());
    // prints "/usr/"
}
```
- [path.join in Node](https://nodejs.org/api/path.html#pathjoinpaths) doesn't add a trailing slash:
```js
const path = require('path');

path.join('/usr', '');
// '/usr'
```
- [filepath.Join in Go](https://pkg.go.dev/path/filepath#Join) doesn't add a trailing slash:
```go
package main

import ("fmt"; "path/filepath")

func main() {
  fmt.Println(filepath.Join("/usr", ""))
  // prints "/usr"
}
```



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