Rollup merge of #123962 - oli-obk:define_opaque_types5, r=lcnr

change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? ```@compiler-errors```

fixes  #121404

cc #116652

Author: matthiaskrgr

compiler/rustc_hir_typeck/src/callee.rs

@@ -628,7 +628,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 return;
             };
 
-            let pick = self.confirm_method(
+            let pick = self.confirm_method_for_diagnostic(
                 call_expr.span,
                 callee_expr,
                 call_expr,

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1418,7 +1418,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let impl_ty = self.normalize(span, tcx.type_of(impl_def_id).instantiate(tcx, args));
             let self_ty = self.normalize(span, self_ty);
             match self.at(&self.misc(span), self.param_env).eq(
-                DefineOpaqueTypes::No,
+                DefineOpaqueTypes::Yes,
                 impl_ty,
                 self_ty,
             ) {

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -497,7 +497,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                 args,
             })),
         );
-        match self.at(&cause, self.param_env).sup(DefineOpaqueTypes::No, method_self_ty, self_ty) {
+        match self.at(&cause, self.param_env).sup(DefineOpaqueTypes::Yes, method_self_ty, self_ty) {
             Ok(InferOk { obligations, value: () }) => {
                 self.register_predicates(obligations);
             }

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -634,8 +634,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
-        debug!("assemble_probe: self_ty={:?}", self_ty);
         let raw_self_ty = self_ty.value.value;
         match *raw_self_ty.kind() {
             ty::Dynamic(data, ..) if let Some(p) = data.principal() => {
@@ -713,13 +713,12 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
         if !self.impl_dups.insert(impl_def_id) {
             return; // already visited
         }
 
-        debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
-
         for item in self.impl_or_trait_item(impl_def_id) {
             if !self.has_applicable_self(&item) {
                 // No receiver declared. Not a candidate.
@@ -737,9 +736,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
-        debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
-
         let principal = match self_ty.kind() {
             ty::Dynamic(ref data, ..) => Some(data),
             _ => None,
@@ -768,9 +766,9 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         });
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
         // FIXME: do we want to commit to this behavior for param bounds?
-        debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
 
         let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
             let bound_predicate = predicate.kind();
@@ -826,6 +824,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn assemble_extension_candidates_for_traits_in_scope(&mut self) {
         let mut duplicates = FxHashSet::default();
         let opt_applicable_traits = self.tcx.in_scope_traits(self.scope_expr_id);
@@ -842,6 +841,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn assemble_extension_candidates_for_all_traits(&mut self) {
         let mut duplicates = FxHashSet::default();
         for trait_info in suggest::all_traits(self.tcx) {
@@ -863,12 +863,12 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn assemble_extension_candidates_for_trait(
         &mut self,
         import_ids: &SmallVec<[LocalDefId; 1]>,
         trait_def_id: DefId,
     ) {
-        debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
         let trait_args = self.fresh_args_for_item(self.span, trait_def_id);
         let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, trait_args);
 
@@ -958,6 +958,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     ///////////////////////////////////////////////////////////////////////////
     // THE ACTUAL SEARCH
 
+    #[instrument(level = "debug", skip(self))]
     fn pick(mut self) -> PickResult<'tcx> {
         assert!(self.method_name.is_some());
 
@@ -1386,6 +1387,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "trace", skip(self, possibly_unsatisfied_predicates), ret)]
     fn consider_probe(
         &self,
         self_ty: Ty<'tcx>,
@@ -1415,15 +1417,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     (xform_self_ty, xform_ret_ty) =
                         self.xform_self_ty(probe.item, impl_ty, impl_args);
                     xform_self_ty = ocx.normalize(cause, self.param_env, xform_self_ty);
-                    // FIXME: Make this `ocx.sup` once we define opaques more eagerly.
-                    match self.at(cause, self.param_env).sup(
-                        DefineOpaqueTypes::No,
-                        xform_self_ty,
-                        self_ty,
-                    ) {
-                        Ok(infer_ok) => {
-                            ocx.register_infer_ok_obligations(infer_ok);
-                        }
+                    match ocx.sup(cause, self.param_env, xform_self_ty, self_ty) {
+                        Ok(()) => {}
                         Err(err) => {
                             debug!("--> cannot relate self-types {:?}", err);
                             return ProbeResult::NoMatch;
@@ -1484,19 +1479,23 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     (xform_self_ty, xform_ret_ty) =
                         self.xform_self_ty(probe.item, trait_ref.self_ty(), trait_ref.args);
                     xform_self_ty = ocx.normalize(cause, self.param_env, xform_self_ty);
-                    // FIXME: Make this `ocx.sup` once we define opaques more eagerly.
-                    match self.at(cause, self.param_env).sup(
-                        DefineOpaqueTypes::No,
-                        xform_self_ty,
-                        self_ty,
-                    ) {
-                        Ok(infer_ok) => {
-                            ocx.register_infer_ok_obligations(infer_ok);
-                        }
-                        Err(err) => {
-                            debug!("--> cannot relate self-types {:?}", err);
+                    match self_ty.kind() {
+                        // HACK: opaque types will match anything for which their bounds hold.
+                        // Thus we need to prevent them from trying to match the `&_` autoref
+                        // candidates that get created for `&self` trait methods.
+                        ty::Alias(ty::Opaque, alias_ty)
+                            if self.infcx.can_define_opaque_ty(alias_ty.def_id)
+                                && !xform_self_ty.is_ty_var() =>
+                        {
                             return ProbeResult::NoMatch;
                         }
+                        _ => match ocx.sup(cause, self.param_env, xform_self_ty, self_ty) {
+                            Ok(()) => {}
+                            Err(err) => {
+                                debug!("--> cannot relate self-types {:?}", err);
+                                return ProbeResult::NoMatch;
+                            }
+                        },
                     }
                     let obligation = traits::Obligation::new(
                         self.tcx,
@@ -1536,15 +1535,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     (xform_self_ty, xform_ret_ty) =
                         self.xform_self_ty(probe.item, trait_ref.self_ty(), trait_ref.args);
                     xform_self_ty = ocx.normalize(cause, self.param_env, xform_self_ty);
-                    // FIXME: Make this `ocx.sup` once we define opaques more eagerly.
-                    match self.at(cause, self.param_env).sup(
-                        DefineOpaqueTypes::No,
-                        xform_self_ty,
-                        self_ty,
-                    ) {
-                        Ok(infer_ok) => {
-                            ocx.register_infer_ok_obligations(infer_ok);
-                        }
+                    match ocx.sup(cause, self.param_env, xform_self_ty, self_ty) {
+                        Ok(()) => {}
                         Err(err) => {
                             debug!("--> cannot relate self-types {:?}", err);
                             return ProbeResult::NoMatch;
@@ -1665,6 +1657,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
     /// candidate method where the method name may have been misspelled. Similarly to other
     /// edit distance based suggestions, we provide at most one such suggestion.
+    #[instrument(level = "debug", skip(self))]
     pub(crate) fn probe_for_similar_candidate(
         &mut self,
     ) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {

compiler/rustc_middle/src/traits/query.rs

@@ -156,7 +156,7 @@ pub struct CandidateStep<'tcx> {
 
 #[derive(Copy, Clone, Debug, HashStable)]
 pub struct MethodAutoderefStepsResult<'tcx> {
-    /// The valid autoderef steps that could be find.
+    /// The valid autoderef steps that could be found.
     pub steps: &'tcx [CandidateStep<'tcx>],
     /// If Some(T), a type autoderef reported an error on.
     pub opt_bad_ty: Option<&'tcx MethodAutoderefBadTy<'tcx>>,

tests/ui/impl-trait/call_method_ambiguous.next.stderr

@@ -0,0 +1,17 @@
+error[E0282]: type annotations needed
+  --> $DIR/call_method_ambiguous.rs:29:13
+   |
+LL |         let mut iter = foo(n - 1, m);
+   |             ^^^^^^^^
+LL |
+LL |         assert_eq!(iter.get(), 1);
+   |                    ---- type must be known at this point
+   |
+help: consider giving `iter` an explicit type
+   |
+LL |         let mut iter: /* Type */ = foo(n - 1, m);
+   |                     ++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0282`.

tests/ui/impl-trait/call_method_ambiguous.rs

@@ -0,0 +1,39 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@[current] run-pass
+
+#![feature(precise_capturing)]
+#![allow(incomplete_features)]
+
+trait Get {
+    fn get(&mut self) -> u32;
+}
+
+impl Get for () {
+    fn get(&mut self) -> u32 {
+        0
+    }
+}
+
+impl<T> Get for &mut T
+where
+    T: Get,
+{
+    fn get(&mut self) -> u32 {
+        T::get(self) + 1
+    }
+}
+
+fn foo(n: usize, m: &mut ()) -> impl use<'_> Get {
+    if n > 0 {
+        let mut iter = foo(n - 1, m);
+        //[next]~^ type annotations needed
+        assert_eq!(iter.get(), 1);
+    }
+    m
+}
+
+fn main() {
+    let g = foo(1, &mut ()).get();
+    assert_eq!(g, 1);
+}

tests/ui/impl-trait/call_method_on_inherent_impl.next.stderr

@@ -0,0 +1,17 @@
+error[E0282]: type annotations needed
+  --> $DIR/call_method_on_inherent_impl.rs:18:13
+   |
+LL |         let x = my_foo();
+   |             ^
+LL |
+LL |         x.my_debug();
+   |         - type must be known at this point
+   |
+help: consider giving `x` an explicit type
+   |
+LL |         let x: /* Type */ = my_foo();
+   |              ++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0282`.

tests/ui/impl-trait/call_method_on_inherent_impl.rs

@@ -0,0 +1,25 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@[current] check-pass
+
+trait MyDebug {
+    fn my_debug(&self);
+}
+
+impl<T> MyDebug for T
+where
+    T: std::fmt::Debug,
+{
+    fn my_debug(&self) {}
+}
+
+fn my_foo() -> impl std::fmt::Debug {
+    if false {
+        let x = my_foo();
+        //[next]~^ type annotations needed
+        x.my_debug();
+    }
+    ()
+}
+
+fn main() {}

tests/ui/impl-trait/call_method_on_inherent_impl_on_rigid_type.current.stderr

@@ -0,0 +1,16 @@
+error[E0599]: no method named `my_debug` found for reference `&impl Debug` in the current scope
+  --> $DIR/call_method_on_inherent_impl_on_rigid_type.rs:16:11
+   |
+LL |         x.my_debug();
+   |           ^^^^^^^^ method not found in `&impl Debug`
+   |
+   = help: items from traits can only be used if the trait is implemented and in scope
+note: `MyDebug` defines an item `my_debug`, perhaps you need to implement it
+  --> $DIR/call_method_on_inherent_impl_on_rigid_type.rs:4:1
+   |
+LL | trait MyDebug {
+   | ^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0599`.

tests/ui/impl-trait/call_method_on_inherent_impl_on_rigid_type.next.stderr

@@ -0,0 +1,17 @@
+error[E0282]: type annotations needed for `&_`
+  --> $DIR/call_method_on_inherent_impl_on_rigid_type.rs:14:13
+   |
+LL |         let x = &my_foo();
+   |             ^
+LL |
+LL |         x.my_debug();
+   |           -------- type must be known at this point
+   |
+help: consider giving `x` an explicit type, where the placeholders `_` are specified
+   |
+LL |         let x: &_ = &my_foo();
+   |              ++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0282`.

tests/ui/impl-trait/call_method_on_inherent_impl_on_rigid_type.rs

@@ -0,0 +1,22 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+
+trait MyDebug {
+    fn my_debug(&self);
+}
+
+impl MyDebug for &() {
+    fn my_debug(&self) {}
+}
+
+fn my_foo() -> impl std::fmt::Debug {
+    if false {
+        let x = &my_foo();
+        //[next]~^ ERROR: type annotations needed
+        x.my_debug();
+        //[current]~^ ERROR: no method named `my_debug`
+    }
+    ()
+}
+
+fn main() {}