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, 3 insertions, 3 deletions

diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 8b41a0ff176..6b64614363f 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -488,13 +488,13 @@ pub fn get_codegen_sysroot(
 }
 
 pub(crate) fn check_attr_crate_type(
-    sess: &Session,
+    _sess: &Session,
     attrs: &[ast::Attribute],
     lint_buffer: &mut LintBuffer,
 ) {
     // Unconditionally collect crate types from attributes to make them used
     for a in attrs.iter() {
-        if sess.check_name(a, sym::crate_type) {
+        if a.has_name(sym::crate_type) {
             if let Some(n) = a.value_str() {
                 if categorize_crate_type(n).is_some() {
                     return;
@@ -552,7 +552,7 @@ pub fn collect_crate_types(session: &Session, attrs: &[ast::Attribute]) -> Vec<C
     let attr_types: Vec<CrateType> = attrs
         .iter()
         .filter_map(|a| {
-            if session.check_name(a, sym::crate_type) {
+            if a.has_name(sym::crate_type) {
                 match a.value_str() {
                     Some(s) => categorize_crate_type(s),
                     _ => None,