Keep array types on same line as prefix for statics

[Blackgaurd]

Fix for: #6976

Mimicking how types are rewritten in rewrite_struct_field:

• Try rewriting type by itself on the rest of the line.
• If it doesn't fit one line, use rewrite_assign_rhs.

[ytmimi]

Thanks for the PR. Before we can consider moving forward these changes need to be gated because they could impact stable default formatting.

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[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[Blackgaurd]

@rustbot ready

[ytmimi]

Could you add a test case where the array type is so large that it doesn't fit within the max_width even after we place it on the next line. I'd like to see what happens in that case. You can either make the type really long or you can artificially reduce the max_width on that test case to see what happens.

@rustbot author

[Blackgaurd]

I've added such a test case, where the type has width 104 > 100 if put on the second line. I believe its output is desired since it mirrors how a similar case with struct fields are formatted. That is,

pub struct T {
    field_name_that_is_kind_of_really_long1: 
        [ThisTypeIsReallyLongAbcdefghikjlmnopqrstuvwxyz; usernames::constants::USERNAME_LINK_ENTROPY_SIZE],
}

becomes

pub struct T {
    field_name_that_is_kind_of_really_long1: 
        [ThisTypeIsReallyLongAbcdefghikjlmnopqrstuvwxyz; usernames::constants::USERNAME_LINK_ENTROPY_SIZE],
}

So the array type is still split in two, with the first part on the first line, and the second part on the second line.

@rustbot ready

[ytmimi]

hmmm 🤔 so when the type is too long we still end up with the same formatting that #6976 was hoping to avoid. To be honest, I'm not sure how to handle this right now. I'd like @rust-lang/style to weigh in on this one before moving forward.

---

Edit: Here's the link to the Zulip discussion: #t-style > Guidance on Array Type wrapping

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