From: "andrykonchin (Andrew Konchin)" <noreply@...>
Date: 2022-08-06T11:41:30+00:00
Subject: [ruby-core:109429] [Ruby master Bug#18956] Kernel#sprintf - %c handles negative Integer argument in a confusing way

Issue #18956 has been reported by andrykonchin (Andrew Konchin).

----------------------------------------
Bug #18956: Kernel#sprintf - %c handles negative Integer argument in a confusing way
https://bugs.ruby-lang.org/issues/18956

* Author: andrykonchin (Andrew Konchin)
* Status: Open
* Priority: Normal
* ruby -v: 3.0.3
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
Integer argument for `%c `means a character codepoint.

I've noticed two outcomes:
- exception
- broken/incorrect string

When exception is raised - its message a bit misleading and confusing:

```ruby
sprintf("%c", -1000)
# => invalid character (ArgumentError)

sprintf("%c".encode('ascii'), -1)
# => 4294967295 out of char range (RangeError)
```

`invalid character` means there is a character, but actual argument is a codepoint. `4294967295 out of char range` is about codepoint, but it mentions `4294967295` instead of actual argument `-1`.

```ruby
sprintf("%c", -1)
# => "\xFF"
```

In this case no exception is risen but the string is not valid:

```ruby
sprintf("%c", -1).codepoints
# => invalid byte sequence in UTF-8 (ArgumentError)
sprintf("%c", -1).valid_encoding?
# => false
```



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