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Split out statement attributes changes from #78306 #78326

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merged 1 commit into from
Oct 25, 2020

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Aaron1011
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This is the same as PR #78306, but unused_doc_comments is modified to explicitly ignore statement items (which preserves the current behavior).

This shouldn't have any user-visible effects, so it can be landed without lang team discussion.


When the 'early' and 'late' visitors visit an attribute target, they
activate any lint attributes (e.g. #[allow]) that apply to it.
This can affect warnings emitted on sibiling attributes. For example,
the following code does not produce an unused_attributes for
#[inline], since the sibiling #[allow(unused_attributes)] suppressed
the warning.

trait Foo {
    #[allow(unused_attributes)] #[inline] fn first();
    #[inline] #[allow(unused_attributes)] fn second();
}

However, we do not do this for statements - instead, the lint attributes
only become active when we visit the struct nested inside StmtKind
(e.g. Item).

Currently, this is difficult to observe due to another issue - the
HasAttrs impl for StmtKind ignores attributes for StmtKind::Item.
As a result, the unused_doc_comments lint will never see attributes on
item statements.

This commit makes two interrelated fixes to the handling of inert
(non-proc-macro) attributes on statements:

  • The HasAttr impl for StmtKind now returns attributes for
    StmtKind::Item, treating it just like every other StmtKind
    variant. The only place relying on the old behavior was macro
    which has been updated to explicitly ignore attributes on item
    statements. This allows the unused_doc_comments lint to fire for
    item statements.
  • The early and late lint visitors now activate lint attributes when
    invoking the callback for Stmt. This ensures that a lint
    attribute (e.g. #[allow(unused_doc_comments)]) can be applied to
    sibiling attributes on an item statement.

For now, the unused_doc_comments lint is explicitly disabled on item
statements, which preserves the current behavior. The exact locatiosn
where this lint should fire are being discussed in PR #78306

When the 'early' and 'late' visitors visit an attribute target, they
activate any lint attributes (e.g. `#[allow]`) that apply to it.
This can affect warnings emitted on sibiling attributes. For example,
the following code does not produce an `unused_attributes` for
`#[inline]`, since the sibiling `#[allow(unused_attributes)]` suppressed
the warning.

```rust
trait Foo {
    #[allow(unused_attributes)] #[inline] fn first();
    #[inline] #[allow(unused_attributes)] fn second();
}
```

However, we do not do this for statements - instead, the lint attributes
only become active when we visit the struct nested inside `StmtKind`
(e.g. `Item`).

Currently, this is difficult to observe due to another issue - the
`HasAttrs` impl for `StmtKind` ignores attributes for `StmtKind::Item`.
As a result, the `unused_doc_comments` lint will never see attributes on
item statements.

This commit makes two interrelated fixes to the handling of inert
(non-proc-macro) attributes on statements:

* The `HasAttr` impl for `StmtKind` now returns attributes for
  `StmtKind::Item`, treating it just like every other `StmtKind`
  variant. The only place relying on the old behavior was macro
  which has been updated to explicitly ignore attributes on item
  statements. This allows the `unused_doc_comments` lint to fire for
  item statements.
* The `early` and `late` lint visitors now activate lint attributes when
  invoking the callback for `Stmt`. This ensures that a lint
  attribute (e.g. `#[allow(unused_doc_comments)]`) can be applied to
  sibiling attributes on an item statement.

For now, the `unused_doc_comments` lint is explicitly disabled on item
statements, which preserves the current behavior. The exact locatiosn
where this lint should fire are being discussed in PR rust-lang#78306
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r? @ecstatic-morse

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 24, 2020
@Aaron1011
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r? @petrochenkov

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@bors r+

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bors commented Oct 24, 2020

📌 Commit ac384ac has been approved by petrochenkov

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 24, 2020
@jyn514 jyn514 added A-attributes Area: Attributes (`#[…]`, `#![…]`) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Oct 24, 2020
bors added a commit to rust-lang-ci/rust that referenced this pull request Oct 25, 2020
Rollup of 8 pull requests

Successful merges:

 - rust-lang#77984 (Compute proper module parent during resolution)
 - rust-lang#78085 (MIR validation should check `SwitchInt` values are valid for the type)
 - rust-lang#78208 (replace `#[allow_internal_unstable]` with `#[rustc_allow_const_fn_unstable]` for `const fn`s)
 - rust-lang#78209 (Update `compiler_builtins` to 0.1.36)
 - rust-lang#78276 (Bump backtrace-rs to enable Mach-O support on iOS.)
 - rust-lang#78320 (Link to cargo's `build-std` feature instead of `xargo` in custom target docs)
 - rust-lang#78322 (BTreeMap: stop mistaking node::MIN_LEN for a node level constraint)
 - rust-lang#78326 (Split out statement attributes changes from rust-lang#78306)

Failed merges:

r? `@ghost`
@bors bors merged commit 0a26e4b into rust-lang:master Oct 25, 2020
@rustbot rustbot added this to the 1.49.0 milestone Oct 25, 2020
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7 participants