[Drop Tracking] Allow uninhabited types in generator interiors

compiler/rustc_mir_transform/src/generator.rs

@@ -740,24 +740,36 @@ fn sanitize_witness<'tcx>(
         }
     };
 
-    for (local, decl) in body.local_decls.iter_enumerated() {
-        // Ignore locals which are internal or not saved between yields.
-        if !saved_locals.contains(local) || decl.internal {
-            continue;
-        }
-        let decl_ty = tcx.normalize_erasing_regions(param_env, decl.ty);
+    // First check if any of the locals are an uninhabited type. If so, we don't need to do the
+    // rest of this check because this code unreachable.
+    let any_uninhabited = body.local_decls.iter_enumerated().any(|(_, decl)| {
+        tcx.is_ty_uninhabited_from(
+            tcx.parent_module(tcx.hir().local_def_id_to_hir_id(did.expect_local())).to_def_id(),
+            tcx.normalize_erasing_regions(param_env, decl.ty),
+            param_env,
+        )
+    });
 
-        // Sanity check that typeck knows about the type of locals which are
-        // live across a suspension point
-        if !allowed.contains(&decl_ty) && !allowed_upvars.contains(&decl_ty) {
-            span_bug!(
-                body.span,
-                "Broken MIR: generator contains type {} in MIR, \
+    if !any_uninhabited {
+        for (local, decl) in body.local_decls.iter_enumerated() {
+            // Ignore locals which are internal or not saved between yields.
+            if !saved_locals.contains(local) || decl.internal {
+                continue;
+            }
+            let decl_ty = tcx.normalize_erasing_regions(param_env, decl.ty);
+
+            // Sanity check that typeck knows about the type of locals which are
+            // live across a suspension point
+            if !allowed.contains(&decl_ty) && !allowed_upvars.contains(&decl_ty) {
+                span_bug!(
+                    body.span,
+                    "Broken MIR: generator contains type {} in MIR, \
                        but typeck only knows about {} and {:?}",
-                decl_ty,
-                allowed,
-                allowed_upvars
-            );
+                    decl_ty,
+                    allowed,
+                    allowed_upvars
+                );
+            }
         }
     }
 }

src/test/ui/async-await/async-fn-nonsend.rs

@@ -47,13 +47,6 @@ async fn non_sync_with_method_call() {
     }
 }
 
-async fn non_sync_with_method_call_panic() {
-    let f: &mut std::fmt::Formatter = panic!();
-    if non_sync().fmt(f).unwrap() == () {
-        fut().await;
-    }
-}
-
 async fn non_sync_with_method_call_infinite_loop() {
     let f: &mut std::fmt::Formatter = loop {};
     if non_sync().fmt(f).unwrap() == () {
@@ -69,6 +62,5 @@ pub fn pass_assert() {
     //~^ ERROR future cannot be sent between threads safely
     assert_send(non_sync_with_method_call());
     //~^ ERROR future cannot be sent between threads safely
-    assert_send(non_sync_with_method_call_panic());
     assert_send(non_sync_with_method_call_infinite_loop());
 }

src/test/ui/async-await/async-fn-nonsend.stderr

@@ -1,5 +1,5 @@
 error: future cannot be sent between threads safely
-  --> $DIR/async-fn-nonsend.rs:68:17
+  --> $DIR/async-fn-nonsend.rs:61:17
    |
 LL |     assert_send(non_send_temporary_in_match());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `non_send_temporary_in_match` is not `Send`
@@ -16,13 +16,13 @@ LL |         Some(_) => fut().await,
 LL | }
    | - `Some(non_send())` is later dropped here
 note: required by a bound in `assert_send`
-  --> $DIR/async-fn-nonsend.rs:64:24
+  --> $DIR/async-fn-nonsend.rs:57:24
    |
 LL | fn assert_send(_: impl Send) {}
    |                        ^^^^ required by this bound in `assert_send`
 
 error: future cannot be sent between threads safely
-  --> $DIR/async-fn-nonsend.rs:70:17
+  --> $DIR/async-fn-nonsend.rs:63:17
    |
 LL |     assert_send(non_sync_with_method_call());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `non_sync_with_method_call` is not `Send`
@@ -40,7 +40,7 @@ LL |     }
 LL | }
    | - `get_formatter()` is later dropped here
 note: required by a bound in `assert_send`
-  --> $DIR/async-fn-nonsend.rs:64:24
+  --> $DIR/async-fn-nonsend.rs:57:24
    |
 LL | fn assert_send(_: impl Send) {}
    |                        ^^^^ required by this bound in `assert_send`

src/test/ui/async-await/drop-never.rs

@@ -0,0 +1,17 @@
+// build-pass
+// compile-flags: -Zdrop-tracking
+// edition:2021
+
+enum Never {}
+
+fn f() -> Never { todo!() }
+
+fn main() {
+    let _ = async {
+        let a = String::new();
+        let b = f();
+        async {}.await;
+        drop(a);
+        drop(b);
+    };
+}

src/test/ui/async-await/issue-93161.rs

@@ -0,0 +1,26 @@
+// edition:2021
+// build-pass
+// compile-flags: -Zdrop-tracking
+
+#![feature(never_type)]
+
+enum Never {}
+fn never() -> Never {
+    panic!()
+}
+
+async fn includes_never(crash: bool, x: u32) -> u32 {
+    let mut result = async { x * x }.await;
+    if !crash {
+        return result;
+    }
+    #[allow(unused)]
+    let bad = never();
+    result *= async { x + x }.await;
+    drop(bad);
+    result
+}
+
+fn main() {
+    let _ = includes_never(false, 4);
+}