[ruby-core:79791] [Ruby trunk Bug#13196] Improve keyword argument errors when non-keyword arguments given

Issue #13196 has been updated by Marcus Stollsteimer.


Olivier Lacan wrote:
> ```diff
> +   if (req_key_num > 0) {
> +       VALUE mesg = rb_attr_get(exc, idMesg);
> +       rb_str_resize(mesg, RSTRING_LEN(mesg)-1);
> +       rb_str_cat_cstr(mesg, "; required keyword");
> +       if (req_key_num > 1) rb_str_cat_cstr(mesg, "s");
> +       do {
> +       rb_str_cat_cstr(mesg, ": ");
> +       rb_str_append(mesg, rb_id2str(*keywords++));
> +       rb_str_cat_cstr(mesg, ",");
> +       } while (--req_key_num);
> ```

* I think `rb_str_cat_cstr(mesg, ": ");` in the while-loop doesn't work; ":" must be added before the loop, in the loop only " " to separate different entries

* suggestion: s/keyword/keyword argument/, since "keyword" might be confused with language keywords like `def`, `end`, ...

Regarding `code` vs. `:code`, IMHO for beginners it's much easier to understand without leading ":", similar to the usage in the call sequence, it's _not_ `explode(:code: 123)` but `explode(code: 123)`, and in the method body.

----------------------------------------
Bug #13196: Improve keyword argument errors when non-keyword arguments given
https://bugs.ruby-lang.org/issues/13196#change-63217

* Author: Olivier Lacan
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
Given the following method definition:


```ruby
def explode(code:)
  puts "Boom!"
end
```

If a Ruby user doesn't provide any arguments when calling the `explode` method, the following helpful feedback is given:

```ruby
explode
ArgumentError: missing keyword: code
```

But when a Ruby user mistakenly provides a regular argument, the exception message is obtuse and unhelpful: 

```ruby
explode "1234"
ArgumentError: wrong number of arguments (given 1, expected 0)
```

This does not provide information to properly recover from the error. Worse, it's incorrect. It is not true that the method expected 0 arguments. The method expected 1 keyword argument.

Instead, Ruby should respond something like: 

```ruby
explode "1234"
ArgumentError: missing keyword: code, given "1234" which is not a keyword argument.
```

One could argue that this situation would call for a different error class, perhaps a `KeywordArgumentError` that would inherit from `ArgumentError`, but that would extend the scope of this feature request a bit too far in my mind. 

---Files--------------------------------
missing_kwargs.diff (1.2 KB)


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