Rollup merge of rust-lang#144534 - RalfJung:should_check_for_sync, r=compiler-errors

check_static_item: explain should_check_for_sync choices

Follow-up to rust-lang#144226.

r? ``@oli-obk``

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/check/check.rs

@@ -768,7 +768,9 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(),
                     check_static_inhabited(tcx, def_id);
                     check_static_linkage(tcx, def_id);
                     let ty = tcx.type_of(def_id).instantiate_identity();
-                    res = res.and(wfcheck::check_static_item(tcx, def_id, ty, true));
+                    res = res.and(wfcheck::check_static_item(
+                        tcx, def_id, ty, /* should_check_for_sync */ true,
+                    ));
                 }
                 DefKind::Const => res = res.and(wfcheck::check_const_item(tcx, def_id)),
                 _ => unreachable!(),

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -221,7 +221,9 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_
                     let ty = icx.lower_ty(ty);
                     // MIR relies on references to statics being scalars.
                     // Verify that here to avoid ill-formed MIR.
-                    match check_static_item(tcx, def_id, ty, false) {
+                    // We skip the `Sync` check to avoid cycles for type-alias-impl-trait,
+                    // relying on the fact that non-Sync statics don't ICE the rest of the compiler.
+                    match check_static_item(tcx, def_id, ty, /* should_check_for_sync */ false) {
                         Ok(()) => ty,
                         Err(guar) => Ty::new_error(tcx, guar),
                     }
@@ -286,7 +288,9 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_
                 let ty = icx.lower_ty(ty);
                 // MIR relies on references to statics being scalars.
                 // Verify that here to avoid ill-formed MIR.
-                match check_static_item(tcx, def_id, ty, false) {
+                // We skip the `Sync` check to avoid cycles for type-alias-impl-trait,
+                // relying on the fact that non-Sync statics don't ICE the rest of the compiler.
+                match check_static_item(tcx, def_id, ty, /* should_check_for_sync */ false) {
                     Ok(()) => ty,
                     Err(guar) => Ty::new_error(tcx, guar),
                 }