Auto merge of #2567 - RalfJung:ci-sparse, r=RalfJung

CI: use cargo sparse registry

CI spends a few minutes downloading the index so this could help.

src/tools/miri/.github/workflows/ci.yml

@@ -12,6 +12,9 @@ on:
   schedule:
     - cron: '5 15 * * *' # At 15:05 UTC every day.
 
+env:
+  CARGO_UNSTABLE_SPARSE_REGISTRY: 'true'
+
 jobs:
   build:
     runs-on: ${{ matrix.os }}
@@ -61,8 +64,8 @@ jobs:
         if: ${{ steps.cache.outputs.cache-hit == 'false' }}
         shell: bash
         run: |
-          cargo install rustup-toolchain-install-master
-          cargo install xargo
+          cargo install -f rustup-toolchain-install-master
+          cargo install -f xargo
 
       - name: Install "master" toolchain
         shell: bash

src/tools/miri/src/concurrency/thread.rs

@@ -386,6 +386,7 @@ impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
         data_race: Option<&mut data_race::GlobalState>,
     ) -> InterpResult<'tcx> {
         if self.threads[joined_thread_id].join_status == ThreadJoinStatus::Detached {
+            // On Windows this corresponds to joining on a closed handle.
             throw_ub_format!("trying to join a detached thread");
         }