Remove `Session.used_attrs` and move logic to `CheckAttrVisitor`

Instead of updating global state to mark attributes as used,
we now explicitly emit a warning when an attribute is used in
an unsupported position. As a side effect, we are to emit more
detailed warning messages (instead of just a generic "unused" message).

`Session.check_name` is removed, since its only purpose was to mark
the attribute as used. All of the callers are modified to use
`Attribute.has_name`

Additionally, `AttributeType::AssumedUsed` is removed - an 'assumed
used' attribute is implemented by simply not performing any checks
in `CheckAttrVisitor` for a particular attribute.

We no longer emit unused attribute warnings for the `#[rustc_dummy]`
attribute - it's an internal attribute used for tests, so it doesn't
mark sense to treat it as 'unused'.

With this commit, a large source of global untracked state is removed.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_middle/src/middle/limits.rs b/compiler/rustc_middle/src/middle/limits.rs
index 7ea4902f4bc..20dcb670cd6 100644
--- a/compiler/rustc_middle/src/middle/limits.rs
+++ b/compiler/rustc_middle/src/middle/limits.rs
@@ -48,7 +48,7 @@ pub fn get_recursion_limit(krate_attrs: &[Attribute], sess: &Session) -> Limit {
 
 fn get_limit(krate_attrs: &[Attribute], sess: &Session, name: Symbol, default: usize) -> Limit {
     for attr in krate_attrs {
-        if !sess.check_name(attr, name) {
+        if !attr.has_name(name) {
             continue;
         }