Auto merge of rust-lang#119531 - petrochenkov:cmpctxt, r=cjgillot

rustc_span: Optimize syntax context comparisons

Including comparisons with root context.

- `eq_ctxt` doesn't require retrieving full `SpanData`, or taking the span interner lock twice.
- Checking `SyntaxContext` for "rootness" is cheaper than extracting a full outer `ExpnData` for it and checking *it* for rootness.

The internal lint for `eq_ctxt` is also tweaked to detect `a.ctxt() != b.ctxt()` in addition to `a.ctxt() == b.ctxt()`.

clippy_lints/src/casts/unnecessary_cast.rs

@@ -145,7 +145,7 @@ pub(super) fn check<'tcx>(
     if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
         if let Some(id) = path_to_local(cast_expr)
             && let Some(span) = cx.tcx.hir().opt_span(id)
-            && span.ctxt() != cast_expr.span.ctxt()
+            && !span.eq_ctxt(cast_expr.span)
         {
             // Binding context is different than the identifiers context.
             // Weird macro wizardry could be involved here.

clippy_lints/src/implicit_hasher.rs

@@ -118,7 +118,7 @@ impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
                 vis.visit_ty(impl_.self_ty);
 
                 for target in &vis.found {
-                    if item.span.ctxt() != target.span().ctxt() {
+                    if !item.span.eq_ctxt(target.span()) {
                         return;
                     }
 

clippy_lints/src/implicit_return.rs

@@ -225,7 +225,7 @@ impl<'tcx> LateLintPass<'tcx> for ImplicitReturn {
         _: LocalDefId,
     ) {
         if (!matches!(kind, FnKind::Closure) && matches!(decl.output, FnRetTy::DefaultReturn(_)))
-            || span.ctxt() != body.value.span.ctxt()
+            || !span.eq_ctxt(body.value.span)
             || in_external_macro(cx.sess(), span)
         {
             return;

clippy_lints/src/methods/option_map_unwrap_or.rs

@@ -67,7 +67,7 @@ pub(super) fn check<'tcx>(
             }
         }
 
-        if unwrap_arg.span.ctxt() != map_span.ctxt() {
+        if !unwrap_arg.span.eq_ctxt(map_span) {
             return;
         }