don't succeed evaluate_obligation query if new opaque types were registered

compiler/rustc_infer/src/infer/mod.rs

@@ -891,6 +891,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
     }
 
+    pub fn opaque_types_added_in_snapshot(&self, snapshot: &CombinedSnapshot<'a, 'tcx>) -> bool {
+        self.inner.borrow().undo_log.opaque_types_in_snapshot(&snapshot.undo_snapshot)
+    }
+
     pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
         self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
     }

compiler/rustc_infer/src/infer/undo_log.rs

@@ -185,6 +185,10 @@ impl<'tcx> InferCtxtUndoLogs<'tcx> {
         })
     }
 
+    pub(crate) fn opaque_types_in_snapshot(&self, s: &Snapshot<'tcx>) -> bool {
+        self.logs[s.undo_len..].iter().any(|log| matches!(log, UndoLog::OpaqueTypes(..)))
+    }
+
     pub(crate) fn region_constraints(
         &self,
     ) -> impl Iterator<Item = &'_ region_constraints::UndoLog<'tcx>> + Clone {

compiler/rustc_infer/src/traits/project.rs

@@ -203,7 +203,7 @@ impl<'tcx> ProjectionCache<'_, 'tcx> {
             Some(&ProjectionCacheEntry::NormalizedTy { ref ty, complete: _ }) => {
                 info!("ProjectionCacheEntry::complete({:?}) - completing {:?}", key, ty);
                 let mut ty = ty.clone();
-                if result == EvaluationResult::EvaluatedToOk {
+                if result.must_apply_considering_regions() {
                     ty.obligations = vec![];
                 }
                 map.insert(key, ProjectionCacheEntry::NormalizedTy { ty, complete: Some(result) });

compiler/rustc_middle/src/traits/select.rs

@@ -176,6 +176,10 @@ pub enum EvaluationResult {
     EvaluatedToOk,
     /// Evaluation successful, but there were unevaluated region obligations.
     EvaluatedToOkModuloRegions,
+    /// Evaluation successful, but need to rerun because opaque types got
+    /// hidden types assigned without it being known whether the opaque types
+    /// are within their defining scope
+    EvaluatedToOkModuloOpaqueTypes,
     /// Evaluation is known to be ambiguous -- it *might* hold for some
     /// assignment of inference variables, but it might not.
     ///
@@ -252,9 +256,11 @@ impl EvaluationResult {
 
     pub fn may_apply(self) -> bool {
         match self {
-            EvaluatedToOk | EvaluatedToOkModuloRegions | EvaluatedToAmbig | EvaluatedToUnknown => {
-                true
-            }
+            EvaluatedToOkModuloOpaqueTypes
+            | EvaluatedToOk
+            | EvaluatedToOkModuloRegions
+            | EvaluatedToAmbig
+            | EvaluatedToUnknown => true,
 
             EvaluatedToErr | EvaluatedToRecur => false,
         }
@@ -264,7 +270,11 @@ impl EvaluationResult {
         match self {
             EvaluatedToUnknown | EvaluatedToRecur => true,
 
-            EvaluatedToOk | EvaluatedToOkModuloRegions | EvaluatedToAmbig | EvaluatedToErr => false,
+            EvaluatedToOkModuloOpaqueTypes
+            | EvaluatedToOk
+            | EvaluatedToOkModuloRegions
+            | EvaluatedToAmbig
+            | EvaluatedToErr => false,
         }
     }
 }

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -777,6 +777,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             Ok(
                 EvaluationResult::EvaluatedToOk
                 | EvaluationResult::EvaluatedToOkModuloRegions
+                | EvaluationResult::EvaluatedToOkModuloOpaqueTypes
                 | EvaluationResult::EvaluatedToAmbig,
             ) => {}
             _ => return false,

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -394,6 +394,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 Err(_) => return Ok(EvaluatedToErr),
             }
 
+            if self.infcx.opaque_types_added_in_snapshot(snapshot) {
+                return Ok(result.max(EvaluatedToOkModuloOpaqueTypes));
+            }
+
             match self.infcx.region_constraints_added_in_snapshot(snapshot) {
                 None => Ok(result),
                 Some(_) => Ok(result.max(EvaluatedToOkModuloRegions)),

compiler/rustc_type_ir/src/lib.rs

@@ -204,14 +204,6 @@ bitflags! {
                                           | TypeFlags::HAS_CT_INFER.bits
                                           | TypeFlags::HAS_TY_PLACEHOLDER.bits
                                           | TypeFlags::HAS_CT_PLACEHOLDER.bits
-                                          // The `evaluate_obligation` query does not return further
-                                          // obligations. If it evaluates an obligation with an opaque
-                                          // type, that opaque type may get compared to another type,
-                                          // constraining it. We would lose this information.
-                                          // FIXME: differentiate between crate-local opaque types
-                                          // and opaque types from other crates, as only opaque types
-                                          // from the local crate can possibly be a local name
-                                          | TypeFlags::HAS_TY_OPAQUE.bits
                                           // We consider 'freshened' types and constants
                                           // to depend on a particular fn.
                                           // The freshening process throws away information,

src/test/ui/impl-trait/auto-trait-leak.rs

@@ -11,7 +11,6 @@ fn main() {
 // return type, which can't depend on the obligation.
 fn cycle1() -> impl Clone {
     //~^ ERROR cycle detected
-    //~| ERROR cycle detected
     send(cycle2().clone());
 
     Rc::new(Cell::new(5))

src/test/ui/impl-trait/auto-trait-leak.stderr

@@ -30,129 +30,47 @@ note: ...which requires building MIR for `cycle1`...
 LL | fn cycle1() -> impl Clone {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires type-checking `cycle1`...
-  --> $DIR/auto-trait-leak.rs:12:1
-   |
-LL | fn cycle1() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires computing type of `cycle2::{opaque#0}`...
-  --> $DIR/auto-trait-leak.rs:20:16
-   |
-LL | fn cycle2() -> impl Clone {
-   |                ^^^^^^^^^^
-note: ...which requires borrow-checking `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
-   |
-LL | fn cycle2() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires processing `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
-   |
-LL | fn cycle2() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires processing MIR for `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
-   |
-LL | fn cycle2() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires unsafety-checking `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
-   |
-LL | fn cycle2() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires building MIR for `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
-   |
-LL | fn cycle2() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires type-checking `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
-   |
-LL | fn cycle2() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: ...which again requires computing type of `cycle1::{opaque#0}`, completing the cycle
-note: cycle used when checking item types in top-level module
-  --> $DIR/auto-trait-leak.rs:1:1
-   |
-LL | / use std::cell::Cell;
-LL | | use std::rc::Rc;
-LL | |
-LL | | fn send<T: Send>(_: T) {}
-...  |
-LL | |     Rc::new(String::from("foo"))
-LL | | }
-   | |_^
-
-error[E0391]: cycle detected when computing type of `cycle1::{opaque#0}`
-  --> $DIR/auto-trait-leak.rs:12:16
+  --> $DIR/auto-trait-leak.rs:14:5
    |
-LL | fn cycle1() -> impl Clone {
-   |                ^^^^^^^^^^
-   |
-note: ...which requires borrow-checking `cycle1`...
-  --> $DIR/auto-trait-leak.rs:12:1
-   |
-LL | fn cycle1() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires processing `cycle1`...
-  --> $DIR/auto-trait-leak.rs:12:1
-   |
-LL | fn cycle1() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires processing MIR for `cycle1`...
-  --> $DIR/auto-trait-leak.rs:12:1
-   |
-LL | fn cycle1() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires unsafety-checking `cycle1`...
-  --> $DIR/auto-trait-leak.rs:12:1
-   |
-LL | fn cycle1() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires building MIR for `cycle1`...
-  --> $DIR/auto-trait-leak.rs:12:1
-   |
-LL | fn cycle1() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires type-checking `cycle1`...
-  --> $DIR/auto-trait-leak.rs:12:1
-   |
-LL | fn cycle1() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     send(cycle2().clone());
+   |     ^^^^
+   = note: ...which requires evaluating trait selection obligation `impl core::clone::Clone: core::marker::Send`...
 note: ...which requires computing type of `cycle2::{opaque#0}`...
-  --> $DIR/auto-trait-leak.rs:20:16
+  --> $DIR/auto-trait-leak.rs:19:16
    |
 LL | fn cycle2() -> impl Clone {
    |                ^^^^^^^^^^
 note: ...which requires borrow-checking `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
+  --> $DIR/auto-trait-leak.rs:19:1
    |
 LL | fn cycle2() -> impl Clone {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires processing `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
+  --> $DIR/auto-trait-leak.rs:19:1
    |
 LL | fn cycle2() -> impl Clone {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires processing MIR for `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
+  --> $DIR/auto-trait-leak.rs:19:1
    |
 LL | fn cycle2() -> impl Clone {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires unsafety-checking `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
+  --> $DIR/auto-trait-leak.rs:19:1
    |
 LL | fn cycle2() -> impl Clone {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires building MIR for `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
+  --> $DIR/auto-trait-leak.rs:19:1
    |
 LL | fn cycle2() -> impl Clone {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires type-checking `cycle2`...
-  --> $DIR/auto-trait-leak.rs:20:1
+  --> $DIR/auto-trait-leak.rs:20:5
    |
-LL | fn cycle2() -> impl Clone {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     send(cycle1().clone());
+   |     ^^^^
+   = note: ...which requires evaluating trait selection obligation `impl core::clone::Clone: core::marker::Send`...
    = note: ...which again requires computing type of `cycle1::{opaque#0}`, completing the cycle
 note: cycle used when checking item types in top-level module
   --> $DIR/auto-trait-leak.rs:1:1
@@ -166,6 +84,6 @@ LL | |     Rc::new(String::from("foo"))
 LL | | }
    | |_^
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0391`.

src/test/ui/type-alias-impl-trait/auto-trait-leakage3.rs

@@ -6,7 +6,6 @@
 mod m {
     type Foo = impl std::fmt::Debug;
     //~^ ERROR: cycle detected when computing type of `m::Foo::{opaque#0}` [E0391]
-    //~| ERROR: cycle detected when computing type of `m::Foo::{opaque#0}` [E0391]
 
     pub fn foo() -> Foo {
         22_u32

src/test/ui/type-alias-impl-trait/auto-trait-leakage3.stderr

@@ -5,35 +5,18 @@ LL |     type Foo = impl std::fmt::Debug;
    |                ^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires type-checking `m::bar`...
-  --> $DIR/auto-trait-leakage3.rs:15:5
+  --> $DIR/auto-trait-leakage3.rs:15:9
    |
-LL |     pub fn bar() {
-   |     ^^^^^^^^^^^^
+LL |         is_send(foo());
+   |         ^^^^^^^
+   = note: ...which requires evaluating trait selection obligation `m::Foo: core::marker::Send`...
    = note: ...which again requires computing type of `m::Foo::{opaque#0}`, completing the cycle
 note: cycle used when checking item types in module `m`
   --> $DIR/auto-trait-leakage3.rs:6:1
    |
 LL | mod m {
    | ^^^^^
 
-error[E0391]: cycle detected when computing type of `m::Foo::{opaque#0}`
-  --> $DIR/auto-trait-leakage3.rs:7:16
-   |
-LL |     type Foo = impl std::fmt::Debug;
-   |                ^^^^^^^^^^^^^^^^^^^^
-   |
-note: ...which requires type-checking `m::bar`...
-  --> $DIR/auto-trait-leakage3.rs:15:5
-   |
-LL |     pub fn bar() {
-   |     ^^^^^^^^^^^^
-   = note: ...which again requires computing type of `m::Foo::{opaque#0}`, completing the cycle
-note: cycle used when checking item types in module `m`
-  --> $DIR/auto-trait-leakage3.rs:6:1
-   |
-LL | mod m {
-   | ^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0391`.

src/test/ui/type-alias-impl-trait/inference-cycle.rs

@@ -4,7 +4,6 @@
 mod m {
     type Foo = impl std::fmt::Debug;
     //~^ ERROR cycle detected
-    //~| ERROR cycle detected
 
     // Cycle: error today, but it'd be nice if it eventually worked
 

src/test/ui/type-alias-impl-trait/inference-cycle.stderr

@@ -5,35 +5,18 @@ LL |     type Foo = impl std::fmt::Debug;
    |                ^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires type-checking `m::bar`...
-  --> $DIR/inference-cycle.rs:15:5
+  --> $DIR/inference-cycle.rs:15:9
    |
-LL |     pub fn bar() {
-   |     ^^^^^^^^^^^^
+LL |         is_send(foo()); // Today: error
+   |         ^^^^^^^
+   = note: ...which requires evaluating trait selection obligation `m::Foo: core::marker::Send`...
    = note: ...which again requires computing type of `m::Foo::{opaque#0}`, completing the cycle
 note: cycle used when checking item types in module `m`
   --> $DIR/inference-cycle.rs:4:1
    |
 LL | mod m {
    | ^^^^^
 
-error[E0391]: cycle detected when computing type of `m::Foo::{opaque#0}`
-  --> $DIR/inference-cycle.rs:5:16
-   |
-LL |     type Foo = impl std::fmt::Debug;
-   |                ^^^^^^^^^^^^^^^^^^^^
-   |
-note: ...which requires type-checking `m::bar`...
-  --> $DIR/inference-cycle.rs:15:5
-   |
-LL |     pub fn bar() {
-   |     ^^^^^^^^^^^^
-   = note: ...which again requires computing type of `m::Foo::{opaque#0}`, completing the cycle
-note: cycle used when checking item types in module `m`
-  --> $DIR/inference-cycle.rs:4:1
-   |
-LL | mod m {
-   | ^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0391`.

src/test/ui/type-alias-impl-trait/issue-98604.rs

@@ -0,0 +1,13 @@
+// edition:2018
+
+type AsyncFnPtr = Box<
+    dyn Fn() -> std::pin::Pin<Box<dyn std::future::Future<Output = ()>>>,
+>;
+
+async fn test() {}
+
+#[allow(unused_must_use)]
+fn main() {
+    Box::new(test) as AsyncFnPtr;
+    //~^ ERROR type mismatch
+}

src/test/ui/type-alias-impl-trait/issue-98604.stderr

@@ -0,0 +1,18 @@
+error[E0271]: type mismatch resolving `<fn() -> impl Future<Output = ()> {test} as FnOnce<()>>::Output == Pin<Box<(dyn Future<Output = ()> + 'static)>>`
+  --> $DIR/issue-98604.rs:11:5
+   |
+LL |     Box::new(test) as AsyncFnPtr;
+   |     ^^^^^^^^^^^^^^ expected struct `Pin`, found opaque type
+   |
+note: while checking the return type of the `async fn`
+  --> $DIR/issue-98604.rs:7:17
+   |
+LL | async fn test() {}
+   |                 ^ checked the `Output` of this `async fn`, found opaque type
+   = note:   expected struct `Pin<Box<(dyn Future<Output = ()> + 'static)>>`
+           found opaque type `impl Future<Output = ()>`
+   = note: required for the cast from `fn() -> impl Future<Output = ()> {test}` to the object type `dyn Fn() -> Pin<Box<(dyn Future<Output = ()> + 'static)>>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0271`.