Rename known_attrs to expanded_inert_attrs and move to rustc_expand

There's no need for this to be (untracked) global state.

compiler/rustc_expand/src/base.rs

@@ -1,6 +1,7 @@
 use crate::expand::{self, AstFragment, Invocation};
 use crate::module::DirOwnership;
 
+use rustc_ast::attr::MarkedAttrs;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Nonterminal};
 use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, TokenStream};
@@ -951,6 +952,10 @@ pub struct ExtCtxt<'a> {
     ///
     /// `Ident` is the module name.
     pub(super) extern_mod_loaded: OnExternModLoaded<'a>,
+    /// When we 'expand' an inert attribute, we leave it
+    /// in the AST, but insert it here so that we know
+    /// not to expand it again.
+    pub(super) expanded_inert_attrs: MarkedAttrs,
 }
 
 impl<'a> ExtCtxt<'a> {
@@ -977,6 +982,7 @@ impl<'a> ExtCtxt<'a> {
             },
             force_mode: false,
             expansions: FxHashMap::default(),
+            expanded_inert_attrs: MarkedAttrs::new(),
         }
     }
 

compiler/rustc_expand/src/expand.rs

@@ -754,7 +754,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     }
                 }
                 SyntaxExtensionKind::NonMacroAttr { mark_used } => {
-                    self.cx.sess.mark_attr_known(&attr);
+                    self.cx.expanded_inert_attrs.mark(&attr);
                     if *mark_used {
                         self.cx.sess.mark_attr_used(&attr);
                     }
@@ -1040,7 +1040,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
         item.visit_attrs(|attrs| {
             attr = attrs
                 .iter()
-                .position(|a| !self.cx.sess.is_attr_known(a) && !is_builtin_attr(a))
+                .position(|a| !self.cx.expanded_inert_attrs.is_marked(a) && !is_builtin_attr(a))
                 .map(|attr_pos| {
                     let attr = attrs.remove(attr_pos);
                     let following_derives = attrs[attr_pos..]

compiler/rustc_session/src/session.rs

@@ -219,7 +219,6 @@ pub struct Session {
     /// Set of enabled features for the current target.
     pub target_features: FxHashSet<Symbol>,
 
-    known_attrs: Lock<MarkedAttrs>,
     used_attrs: Lock<MarkedAttrs>,
 
     /// `Span`s for `if` conditions that we have suggested turning into `if let`.
@@ -1076,14 +1075,6 @@ impl Session {
             == config::InstrumentCoverage::ExceptUnusedFunctions
     }
 
-    pub fn mark_attr_known(&self, attr: &Attribute) {
-        self.known_attrs.lock().mark(attr)
-    }
-
-    pub fn is_attr_known(&self, attr: &Attribute) -> bool {
-        self.known_attrs.lock().is_marked(attr)
-    }
-
     pub fn mark_attr_used(&self, attr: &Attribute) {
         self.used_attrs.lock().mark(attr)
     }
@@ -1389,7 +1380,6 @@ pub fn build_session(
         miri_unleashed_features: Lock::new(Default::default()),
         asm_arch,
         target_features: FxHashSet::default(),
-        known_attrs: Lock::new(MarkedAttrs::new()),
         used_attrs: Lock::new(MarkedAttrs::new()),
         if_let_suggestions: Default::default(),
     };