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Fix inconsistencies in handling of inert attributes on statements

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 #78306
This commit is contained in:
Aaron Hill 2020-10-23 18:17:00 -04:00
parent 07a63e6d1f
commit ac384ac2db
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GPG key ID: B4087E510E98B164
12 changed files with 94 additions and 22 deletions

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@ -623,7 +623,8 @@ impl HasAttrs for StmtKind {
match *self {
StmtKind::Local(ref local) => local.attrs(),
StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => expr.attrs(),
StmtKind::Empty | StmtKind::Item(..) => &[],
StmtKind::Item(ref item) => item.attrs(),
StmtKind::Empty => &[],
StmtKind::MacCall(ref mac) => mac.attrs.attrs(),
}
}
@ -632,7 +633,8 @@ impl HasAttrs for StmtKind {
match self {
StmtKind::Local(local) => local.visit_attrs(f),
StmtKind::Expr(expr) | StmtKind::Semi(expr) => expr.visit_attrs(f),
StmtKind::Empty | StmtKind::Item(..) => {}
StmtKind::Item(item) => item.visit_attrs(f),
StmtKind::Empty => {}
StmtKind::MacCall(mac) => {
mac.attrs.visit_attrs(f);
}