Objective

Fixes #8906

#8906 reports that the reflect attribute silently fails when using the #[reflect[...]] syntax. I wasn't able to reproduce that issue, so it was likely resolved in a prior change. This pull request addresses only the syntax issue.

Solution

Validate the Meta::List delimiter in reflect macro to allow only MacroDelimiter::Paren

Testing

• Did you test these changes? If so, how?
  I run cargo check --example reflection_types
• Are there any parts that need more testing?
  No
• How can other people (reviewers) test your changes? Is there anything specific they need to know?
  Run cargo check --example reflection_types

Then modify the reflection_types example by changing:

#[reflect(Hash, PartialEq, Clone)]
pub struct E {
    x: usize,
}

to

#[reflect[Hash, PartialEq, Clone]]
pub struct E {
    x: usize,
}

then run cargo check --example reflection_types again it should now fail with this error:

error: `#[reflect = "..."]` must use parenthesis `(` and `)`