Prevent dependency cycle with -Zthir-unsafeck

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -399,21 +399,31 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 fake_reads: _,
             } => {
                 let closure_id = closure_id.expect_local();
-                let closure_def = if let Some((did, const_param_id)) =
-                    ty::WithOptConstParam::try_lookup(closure_id, self.tcx)
-                {
-                    ty::WithOptConstParam { did, const_param_did: Some(const_param_id) }
-                } else {
-                    ty::WithOptConstParam::unknown(closure_id)
-                };
-                let (closure_thir, expr) = self.tcx.thir_body(closure_def);
-                let closure_thir = &closure_thir.borrow();
-                let hir_context = self.tcx.hir().local_def_id_to_hir_id(closure_id);
-                let mut closure_visitor =
-                    UnsafetyVisitor { thir: closure_thir, hir_context, ..*self };
-                closure_visitor.visit_expr(&closure_thir[expr]);
-                // Unsafe blocks can be used in closures, make sure to take it into account
-                self.safety_context = closure_visitor.safety_context;
+                let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(closure_id);
+
+                // Closures in AnonConsts are handled separately to avoid cycles (issue #87414).
+                if !matches!(
+                    self.tcx.hir().get(self.tcx.hir().enclosing_body_owner(closure_hir_id)),
+                    hir::Node::AnonConst(_)
+                ) {
+                    let closure_def = if let Some((did, const_param_id)) =
+                        ty::WithOptConstParam::try_lookup(closure_id, self.tcx)
+                    {
+                        ty::WithOptConstParam { did, const_param_did: Some(const_param_id) }
+                    } else {
+                        ty::WithOptConstParam::unknown(closure_id)
+                    };
+                    let (closure_thir, expr) = self.tcx.thir_body(closure_def);
+                    let closure_thir = &closure_thir.borrow();
+                    let mut closure_visitor = UnsafetyVisitor {
+                        thir: closure_thir,
+                        hir_context: closure_hir_id,
+                        ..*self
+                    };
+                    closure_visitor.visit_expr(&closure_thir[expr]);
+                    // Unsafe blocks can be used in closures, make sure to take it into account
+                    self.safety_context = closure_visitor.safety_context;
+                }
             }
             ExprKind::Field { lhs, .. } => {
                 let lhs = &self.thir[lhs];
@@ -597,11 +607,19 @@ pub fn check_unsafety<'tcx>(tcx: TyCtxt<'tcx>, def: ty::WithOptConstParam<LocalD
         return;
     }
 
-    // Closures are handled by their owner, if it has a body
+    let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
+
+    // Closures are handled by their owner, if it has a body, except if the
+    // closure occurs in an AnonConst body to avoid a cycle (issue #87414)
     if tcx.is_closure(def.did.to_def_id()) {
-        let owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;
-        let owner_hir_id = tcx.hir().local_def_id_to_hir_id(owner);
+        let encl_body_owner = tcx.hir().enclosing_body_owner(hir_id);
+        if matches!(tcx.hir().get(encl_body_owner), hir::Node::AnonConst(_)) {
+            tcx.ensure().thir_check_unsafety(tcx.hir().local_def_id(encl_body_owner));
+            return;
+        }
 
+        let owner = hir_id.owner;
+        let owner_hir_id = tcx.hir().local_def_id_to_hir_id(owner);
         if tcx.hir().maybe_body_owned_by(owner_hir_id).is_some() {
             tcx.ensure().thir_check_unsafety(owner);
             return;
@@ -615,7 +633,6 @@ pub fn check_unsafety<'tcx>(tcx: TyCtxt<'tcx>, def: ty::WithOptConstParam<LocalD
         return;
     }
 
-    let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
     let body_unsafety = tcx.hir().fn_sig_by_hir_id(hir_id).map_or(BodyUnsafety::Safe, |fn_sig| {
         if fn_sig.header.unsafety == hir::Unsafety::Unsafe {
             BodyUnsafety::Unsafe(fn_sig.span)

src/test/ui/unsafe/issue-87414-query-cycle.rs

@@ -0,0 +1,15 @@
+// Regression test for #87414.
+
+// check-pass
+// compile-flags: -Zthir-unsafeck
+
+fn bad<T>() -> Box<dyn Iterator<Item = [(); { |x: u32| { x }; 4 }]>> { todo!() }
+
+fn foo() -> [(); { |x: u32| { x }; 4 }] { todo!() }
+fn bar() { let _: [(); { |x: u32| { x }; 4 }]; }
+
+// This one should not cause any errors either:
+unsafe fn unsf() {}
+fn bad2<T>() -> Box<dyn Iterator<Item = [(); { unsafe { || { unsf() } }; 4 }]>> { todo!() }
+
+fn main() {}