parser: not insert dummy field in struct

[bvanjoi]

Fixes #114636

This PR eliminates the dummy field, initially introduced in #113999, thereby enabling unrestricted use of ident.unwrap(). A side effect of this action is that we can only report the error of the first macro invocation field within the struct node.

An alternative solution might be giving a virtual name to the macro, but it appears more complex.(#114636 (comment)). Furthermore, if you think #114636 (comment) is a better solution, feel free to close this PR.

[bvanjoi]

cc @Centri3

[rustbot]

r? @compiler-errors

(rustbot has picked a reviewer for you, use r? to override)

[compiler-errors]

This is a somewhat sad regression but it's fine imo

[compiler-errors]

r=me when ci is green

@bors delegate+ rollup

[bors]

✌️ @bvanjoi, you can now approve this pull request!

If @compiler-errors told you to "r=me" after making some further change, please make that change, then do @bors r=@compiler-errors

[Centri3]

An alternative solution might be giving a virtual name to the macro, but it appears more complex.

It really isn't. You can easily give it its name by using the already parsed name variable, though I think having multiple fields with the same name is probably breaking an invariant of named structs. Maybe not? I'm not sure but I think this is something disallowed really early on, as afaik macro expansion doesn't even happen if there are multiple fields with the same name.

Instead, I think, if you want to go through the trouble, make parse_name_and_ty return an Option<FieldDef> and push it onto the field list only if it's Some. Otherwise, just continue and act as though it never existed.

We'll also need to edit parse_single_struct_field and parse_field_def. After that, since it unwraps the Err there, we can just not push it if it's None.

This shouldn't even be that big of a performance regression since all it is is usually a pointer under the hood, and a single null check after the call.

[bvanjoi]

make parse_name_and_ty return an Option and push it onto the field list only if it's Some

This represents an improved solution.

@rustbot ready

[compiler-errors]

Sorry for the back and forth @bvanjoi, but I thought about this some more and I'm not convinced that all of the changes are worth it. Let's just go with the simple approach and bail eagerly.

[compiler-errors]

@rustbot author

[bvanjoi]

Sorry for the back and forth

Not to worry. As a beginner, every piece of advice is invaluable.

@rustbot ready

[compiler-errors]

@bors r+ rollup

[bors]

📌 Commit 3ed435f has been approved by compiler-errors

It is now in the queue for this repository.