Auto merge of rust-lang#146919 - lcnr:yeet-fast-path, r=fee1-dead

remove incorrect fast path

Using `tcx.is_copy_modulo_regions` drops information from the current `typing_env`. Writing a regression test for this is really hard. We need to prove `Copy` of something that doesn't directly reference a coroutine or an opaque, but does so indirectly.

cc rust-lang#146813.

Author: bors

compiler/rustc_trait_selection/src/infer.rs

@@ -9,7 +9,7 @@ use rustc_middle::infer::canonical::{
     Canonical, CanonicalQueryInput, CanonicalQueryResponse, QueryResponse,
 };
 use rustc_middle::traits::query::NoSolution;
-use rustc_middle::ty::{self, GenericArg, Ty, TyCtxt, TypeFoldable, TypeVisitableExt, Upcast};
+use rustc_middle::ty::{self, GenericArg, Ty, TyCtxt, TypeFoldable, Upcast};
 use rustc_span::DUMMY_SP;
 use tracing::instrument;
 
@@ -31,19 +31,7 @@ impl<'tcx> InferCtxt<'tcx> {
 
     fn type_is_copy_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
         let ty = self.resolve_vars_if_possible(ty);
-
-        // FIXME(#132279): This should be removed as it causes us to incorrectly
-        // handle opaques in their defining scope, and stalled coroutines.
-        if !self.next_trait_solver() && !(param_env, ty).has_infer() && !ty.has_coroutines() {
-            return self.tcx.type_is_copy_modulo_regions(self.typing_env(param_env), ty);
-        }
-
         let copy_def_id = self.tcx.require_lang_item(LangItem::Copy, DUMMY_SP);
-
-        // This can get called from typeck (by euv), and `moves_by_default`
-        // rightly refuses to work with inference variables, but
-        // moves_by_default has a cache, which we want to use in other
-        // cases.
         traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, copy_def_id)
     }
 

tests/ui/coroutine/copy-fast-path-query-cycle.rs

@@ -0,0 +1,40 @@
+//@ edition: 2024
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ check-pass
+
+// Regression test for #146813. We previously used a pseudo-canonical
+// query during HIR typeck which caused a query cycle when looking at the
+// witness of a coroutine.
+
+use std::future::Future;
+
+trait ConnectMiddleware {}
+
+trait ConnectHandler: Sized {
+    fn with<M>(self, _: M) -> impl ConnectHandler
+    where
+        M: ConnectMiddleware,
+    {
+        LayeredConnectHandler
+    }
+}
+
+struct LayeredConnectHandler;
+impl ConnectHandler for LayeredConnectHandler {}
+impl<F> ConnectHandler for F where F: FnOnce() {}
+
+impl<F, Fut> ConnectMiddleware for F
+where
+    F: FnOnce() -> Fut,
+    Fut: Future<Output = ()> + Send,
+{
+}
+
+pub async fn fails() {
+    { || {} }
+        .with(async || ())
+        .with(async || ())
+        .with(async || ());
+}
+fn main() {}