Prevent to compute Item attributes twice

[GuillaumeGomez]

I came across this case when working on another part of rustdoc. Not a game changer but a nice little improvement.

cc @camelid

r? @jyn514

[pickfire]

Looks good to me although I am not quite sure where are we calculating item attributes twice.

[GuillaumeGomez]

@pickfire We compute them in Item::from_hir_id_and_parts and then we replace the attrs field with the value returned by merged_attrs. :)

[bugadani]

How common is the case where attrs are empty? That box I think can be optimized (by turning the field into Option<Box<>>). I was planning on doing that, but unless it's a bigger change, it could probably be part of this PR.

Not entirely sure, though.

[GuillaumeGomez]

I wouldn't bet on that to be honest. Trying to be too clever never ends well.

[bugadani]

We'll see, I guess I'll submit a PR anyway. But true, the additional complexity might backfire a bit.

[jyn514]

I don't think I'd call that too clever. @bugadani I'd be interested in seeing that PR :)

[jyn514]

@bors r+

[bors]

📌 Commit 0e07904 has been approved by jyn514

[GuillaumeGomez]

@bors: rollup

[jyn514]

@bors rollup=iffy

This affects perf.

[Dylan-DPC-zz]

failed in rollup

@bors r-

[jyn514]

error[E0308]: mismatched types
   --> src/librustdoc/clean/types.rs:175:34
    |
175 |             source: source.clean(cx),
    |                                  ^^ types differ in mutability
    |
    = note: expected mutable reference `&mut DocContext<'_>`
                       found reference `&DocContext<'_>`
error[E0308]: mismatched types
   --> src/librustdoc/clean/types.rs:177:57
    |
    |
177 |             visibility: cx.tcx.visibility(def_id).clean(cx),
    |                                                         ^^ types differ in mutability
    |
    = note: expected mutable reference `&mut DocContext<'_>`
                       found reference `&DocContext<'_>`
error: aborting due to 2 previous errors

@GuillaumeGomez this had a semantic conflict, it needs to be rebased.

[GuillaumeGomez]

Rebased!

@bors: r=jyn514

[bors]

📌 Commit cc0d531 has been approved by jyn514

[bors]

⌛ Testing commit cc0d531 with merge b36f770...

[bors]

☀️ Test successful - checks-actions
Approved by: jyn514
Pushing b36f770 to master...