Auto merge of #79519 - cjgillot:noattr, r=wesleywiser

Store HIR attributes in a side table

Same idea as #72015 but for attributes.
The objective is to reduce incr-comp invalidations due to modified attributes.
Notably, those due to modified doc comments.

Implementation:
- collect attributes during AST->HIR lowering, in `LocalDefId -> ItemLocalId -> &[Attributes]` nested tables;
- access the attributes through a `hir_owner_attrs` query;
- local refactorings to use this access;
- remove `attrs` from HIR data structures one-by-one.

Change in behaviour:
- the HIR visitor traverses all attributes at once instead of parent-by-parent;
- attribute arrays are sometimes duplicated: for statements and variant constructors;
- as a consequence, attributes are marked as used after unused-attribute lint emission to avoid duplicate lints.

~~Current bug: the lint level is not correctly applied in `std::backtrace_rs`, triggering an unused attribute warning on `#![no_std]`. I welcome suggestions.~~

compiler/rustc_typeck/src/check/method/suggest.rs

@@ -1466,11 +1466,12 @@ impl intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
                     if self.span.map_or(true, |span| item.span < span) {
                         if !item.span.from_expansion() {
                             // Don't insert between attributes and an item.
-                            if item.attrs.is_empty() {
+                            let attrs = self.tcx.hir().attrs(item.hir_id());
+                            if attrs.is_empty() {
                                 self.span = Some(item.span.shrink_to_lo());
                             } else {
                                 // Find the first attribute on the item.
-                                for attr in item.attrs {
+                                for attr in attrs {
                                     if self.span.map_or(true, |span| attr.span < span) {
                                         self.span = Some(attr.span.shrink_to_lo());
                                     }

compiler/rustc_typeck/src/check/regionck.rs

@@ -354,7 +354,7 @@ impl<'a, 'tcx> Visitor<'tcx> for RegionCtxt<'a, 'tcx> {
         hir_id: hir::HirId,
     ) {
         assert!(
-            matches!(fk, intravisit::FnKind::Closure(..)),
+            matches!(fk, intravisit::FnKind::Closure),
             "visit_fn invoked for something other than a closure"
         );
 

compiler/rustc_typeck/src/lib.rs

@@ -201,7 +201,8 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: LocalDefId) {
                         error = true;
                     }
 
-                    for attr in it.attrs {
+                    let attrs = tcx.hir().attrs(main_id);
+                    for attr in attrs {
                         if tcx.sess.check_name(attr, sym::track_caller) {
                             tcx.sess
                                 .struct_span_err(
@@ -300,7 +301,8 @@ fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: LocalDefId) {
                         error = true;
                     }
 
-                    for attr in it.attrs {
+                    let attrs = tcx.hir().attrs(start_id);
+                    for attr in attrs {
                         if tcx.sess.check_name(attr, sym::track_caller) {
                             tcx.sess
                                 .struct_span_err(