[ruby-core:118973] [Ruby master Bug#20700] `warn_cr_in_shebang()` doesn't fire if there's no `\n`

["nobu (Nobuyoshi Nakada) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20700 has been updated by nobu (Nobuyoshi Nakada).

Status changed from Open to Feedback

First of all, not all operating systems consider a line that doesn't end with a newline to be a shebang.

For example, a file with `"#!/x\n"` fails as "cannot execute: required file not found" both on Linux and macOS.
However, a file with `"#!/x"`, no newline, just runs silently on macOS while fails on Linux as well as the above.

In addition, prism does not consider a line like macOS.
```shell-session
$ echo -ne $'#!ruby -Ex' | ruby -wc
ruby: unknown encoding name - x (RuntimeError)
bash: exit 1
```
```shell-session
$ echo -ne $'#!ruby -Ex' | ruby -wc --parser=prism
Syntax OK
```

----------------------------------------
Bug #20700: `warn_cr_in_shebang()` doesn't fire if there's no `\n`
https://bugs.ruby-lang.org/issues/20700#change-109546

* Author: AMomchilov (Alexander Momchilov)
* Status: Feedback
* ruby -v: ruby 3.3.4 (2024-07-09 revision be1089c8ec) [arm64-darwin23]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
The `warn_cr_in_shebang()` function looks for `\r\n` together, but the `\r` should emit a warning, regardless if there's also a `\n` or not.

```ruby
#!/usr/bin/ruby

require "tempfile"
require "open3"

def run_rb(ruby_src)
  puts "===== Output of #{ruby_src.inspect}:"
  Tempfile.create("script.rb") do |f|
    f.print(ruby_src)
    f.close
    
    stdout_and_stderr_str, status = Open3.capture2e("/opt/rubies/3.3.4/bin/ruby", f.path)
    raise unless status.success?
    puts stdout_and_stderr_str
  end
end

run_rb("#!ruby")     # ✅ no warning
run_rb("#!ruby\r")   # ❌ no warning!
run_rb("#!ruby\r\n") # ✅ warns
run_rb("#!ruby -Eutf-8\r\n123") # ✅ warns
```



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