[ruby-core:110155] [Ruby master Bug#19033] One-liner pattern match as Boolean arg syntax error

["baweaver (Brandon Weaver)" <noreply@ruby-lang.org>]

Issue #19033 has been updated by baweaver (Brandon Weaver).


Addendum: We did find that `expect((value in pattern))` works, but not `expect(value in pattern)`, which is where we find things to be confusing

----------------------------------------
Bug #19033: One-liner pattern match as Boolean arg syntax error
https://bugs.ruby-lang.org/issues/19033#change-99412

* Author: baweaver (Brandon Weaver)
* Status: Open
* Priority: Normal
* ruby -v: 3.0.2
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
I was chatting earlier with Seb Wilgosz about pattern matching in tests, and suggested that he might consider the following:

```ruby
expect result in pattern
```

...but he reported back this will syntax error, including with parens:

```ruby
res = [:not_found, 999]
expect(res in [:not_found, *payload])
# => SyntaxError:
# /spec/app/interactors/articles/publish_spec.rb:13: syntax error, unexpected `in', expecting ')'
```

Interestingly though the following work:

```ruby
res = [:not_found, 999]

expect(res) in([:not_found, *payload])
# 1 example, 0 failures
expect(res) in([:not_found, 1, 3])
# 1 example, 0 failures
```

While this appears like an RSpec issue I would contend that it is reproducible with any other method that takes a boolean-like argument.

For me this feels like a syntax bug, but could see a case where it may be interpreted as ambiguous depending on the precedence of `in` relative to method arguments much like `method_name value if condition` is vague between `method_name(value) if condition` and `method_name(value if condition)`. That'll be especially difficult if it's `method_name value in pattern if condition`, so I do not envy parser writers here.

Would be curious for thoughts on that, or if we're looking at that wrong.



-- 
https://bugs.ruby-lang.org/