From 41baa090ad1c40a7fc96f96664543ce4c26746c2 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 26 Sep 2020 18:43:19 -0700
Subject: [PATCH] Skip dropck::check_drop_impl in
 is_const_item_without_destructor

adt_destructor by default also validates the Drop impl using
dropck::check_drop_impl, which contains an expect_local(). This
leads to ICE in check_const_item_mutation if the const's type is
not a local type.

    thread 'rustc' panicked at 'DefId::expect_local: `DefId(5:4805 ~ alloc[d7e9]::vec::{impl#50})` isn't local', compiler/rustc_span/src/def_id.rs:174:43
    stack backtrace:
       0: rust_begin_unwind
       1: rustc_span::def_id::DefId::expect_local::{{closure}}
       2: rustc_typeck::check::dropck::check_drop_impl
       3: rustc_middle::ty::util::<impl rustc_middle::ty::context::TyCtxt>::calculate_dtor::{{closure}}
       4: rustc_middle::ty::trait_def::<impl rustc_middle::ty::context::TyCtxt>::for_each_relevant_impl
       5: rustc_middle::ty::util::<impl rustc_middle::ty::context::TyCtxt>::calculate_dtor
       6: rustc_typeck::check::adt_destructor
       7: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::adt_destructor>::compute
       8: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
       9: rustc_query_system::query::plumbing::get_query_impl
      10: rustc_mir::transform::check_const_item_mutation::ConstMutationChecker::is_const_item_without_destructor
---
 compiler/rustc_mir/src/transform/check_const_item_mutation.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_mir/src/transform/check_const_item_mutation.rs b/compiler/rustc_mir/src/transform/check_const_item_mutation.rs
index 112c25a312930..98477b032372e 100644
--- a/compiler/rustc_mir/src/transform/check_const_item_mutation.rs
+++ b/compiler/rustc_mir/src/transform/check_const_item_mutation.rs
@@ -34,6 +34,7 @@ impl<'a, 'tcx> ConstMutationChecker<'a, 'tcx> {
 
     fn is_const_item_without_destructor(&self, local: Local) -> Option<DefId> {
         let def_id = self.is_const_item(local)?;
+        let mut any_dtor = |_tcx, _def_id| Ok(());
 
         // We avoid linting mutation of a const item if the const's type has a
         // Drop impl. The Drop logic observes the mutation which was performed.
@@ -46,7 +47,7 @@ impl<'a, 'tcx> ConstMutationChecker<'a, 'tcx> {
         //
         //     LOG.msg = "wow";  // prints "wow"
         //
-        match self.tcx.adt_destructor(def_id) {
+        match self.tcx.calculate_dtor(def_id, &mut any_dtor) {
             Some(_) => None,
             None => Some(def_id),
         }