Actually just make can_eq process obligations (almost) everywhere

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -21,6 +21,7 @@ use rustc_middle::ty::{
 use rustc_middle::ty::{GenericParamDefKind, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_span::Span;
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -29,6 +29,7 @@ use rustc_session::parse::feature_err;
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::abi::Abi;
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::misc::{
@@ -1712,15 +1713,7 @@ fn receiver_is_valid<'tcx>(
     let cause =
         ObligationCause::new(span, wfcx.body_def_id, traits::ObligationCauseCode::MethodReceiver);
 
-    let can_eq_self = |ty| {
+    let can_eq_self = |ty| infcx.can_eq(wfcx.param_env, self_ty, ty);
-        wfcx.infcx.probe(|_| {
-            let ocx = ObligationCtxt::new(wfcx.infcx);
-            let Ok(()) = ocx.eq(&ObligationCause::dummy(), wfcx.param_env, self_ty, ty) else {
-                return false;
-            };
-            ocx.select_where_possible().is_empty()
-        })
-    };
 
     // `self: Self` is always valid.
     if can_eq_self(receiver_ty) {

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -49,6 +49,7 @@ use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::{sym, Span, DUMMY_SP};
 use rustc_target::spec::abi;
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::wf::object_region_bounds;
 use rustc_trait_selection::traits::{self, ObligationCtxt};
 

compiler/rustc_hir_typeck/src/demand.rs

@@ -13,6 +13,7 @@ use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, AssocItem, Ty, TypeFoldable, TypeVisitableExt};
 use rustc_span::symbol::sym;
 use rustc_span::{Span, DUMMY_SP};
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::ObligationCause;
 
 use super::method::probe;

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -40,6 +40,7 @@ use rustc_middle::{bug, span_bug};
 use rustc_session::Session;
 use rustc_span::symbol::{kw, Ident};
 use rustc_span::{sym, BytePos, Span, DUMMY_SP};
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::{self, ObligationCauseCode, SelectionContext};
 
 use std::iter;

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -2582,7 +2582,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
             }
             (hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, expr), _, &ty::Ref(_, checked, _))
-                if self.can_sub(self.param_env, checked, expected) =>
+                if self.can_eq(self.param_env, checked, expected) =>
             {
                 let make_sugg = |start: Span, end: BytePos| {
                     // skip `(` for tuples such as `(c) = (&123)`.

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -33,6 +33,7 @@ use rustc_span::edit_distance::{
 };
 use rustc_span::symbol::sym;
 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
+use rustc_trait_selection::infer::InferCtxtExt as _;
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
 use rustc_trait_selection::traits::query::method_autoderef::{
@@ -857,7 +858,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 let args = self.fresh_args_for_item(self.span, method.def_id);
                 let fty = self.tcx.fn_sig(method.def_id).instantiate(self.tcx, args);
                 let fty = self.instantiate_binder_with_fresh_vars(self.span, infer::FnCall, fty);
-                self.can_sub(self.param_env, fty.output(), expected)
+                self.can_eq(self.param_env, fty.output(), expected)
             }),
             _ => false,
         }

compiler/rustc_hir_typeck/src/pat.rs

@@ -19,6 +19,7 @@ use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, Span, DUMMY_SP};
 use rustc_target::abi::FieldIdx;
+use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode};
 use ty::VariantDef;
 

compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs

@@ -820,7 +820,7 @@ fn foo(&self) -> Self::T { String::new() }
                                 tcx.defaultness(item.id.owner_id)
                             {
                                 let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
-                                if self.infcx.can_eq(param_env, assoc_ty, found) {
+                                if self.infcx.can_eq_shallow(param_env, assoc_ty, found) {
                                     diag.span_label(
                                         item.span,
                                         "associated type defaults can't be assumed inside the \
@@ -843,7 +843,7 @@ fn foo(&self) -> Self::T { String::new() }
                         let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
                         if let hir::Defaultness::Default { has_value: true } =
                             tcx.defaultness(item.id.owner_id)
-                            && self.infcx.can_eq(param_env, assoc_ty, found)
+                            && self.infcx.can_eq_shallow(param_env, assoc_ty, found)
                         {
                             diag.span_label(
                                 item.span,

compiler/rustc_infer/src/infer/mod.rs

@@ -769,21 +769,7 @@ impl<'tcx> InferCtxt<'tcx> {
 
     // FIXME(-Znext-solver): Get rid of this method, it's never correct. Either that,
     // or we need to process the obligations.
-    pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, expected: T, actual: T) -> bool
+    pub fn can_eq_shallow<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
-    where
-        T: at::ToTrace<'tcx>,
-    {
-        let origin = &ObligationCause::dummy();
-        self.probe(|_| {
-            // We're only answering whether there could be a subtyping relation, and with
-            // opaque types, "there could be one", via registering a hidden type.
-            self.at(origin, param_env).sub(DefineOpaqueTypes::Yes, expected, actual).is_ok()
-        })
-    }
-
-    // FIXME(-Znext-solver): Get rid of this method, it's never correct. Either that,
-    // or we need to process the obligations.
-    pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
     where
         T: at::ToTrace<'tcx>,
     {

compiler/rustc_trait_selection/src/infer.rs

@@ -1,3 +1,4 @@
+use crate::infer::at::ToTrace;
 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
 use crate::traits::{self, Obligation, ObligationCause, ObligationCtxt, SelectionContext};
 
@@ -17,6 +18,16 @@ pub use rustc_infer::infer::*;
 
 #[extension(pub trait InferCtxtExt<'tcx>)]
 impl<'tcx> InferCtxt<'tcx> {
+    fn can_eq<T: ToTrace<'tcx>>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool {
+        self.probe(|_| {
+            let ocx = ObligationCtxt::new(self);
+            let Ok(()) = ocx.eq(&ObligationCause::dummy(), param_env, a, b) else {
+                return false;
+            };
+            ocx.select_where_possible().is_empty()
+        })
+    }
+
     fn type_is_copy_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
         let ty = self.resolve_vars_if_possible(ty);
 

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

@@ -1,5 +1,10 @@
 use super::{ObligationCauseCode, PredicateObligation};
+use crate::errors::{
+    EmptyOnClauseInOnUnimplemented, InvalidOnClauseInOnUnimplemented, NoValueInOnUnimplemented,
+};
 use crate::infer::error_reporting::TypeErrCtxt;
+use crate::infer::InferCtxtExt;
+use crate::traits::error_reporting::type_err_ctxt_ext::InferCtxtPrivExt;
 use rustc_ast::AttrArgs;
 use rustc_ast::AttrArgsEq;
 use rustc_ast::AttrKind;
@@ -21,12 +26,6 @@ use rustc_span::Span;
 use std::iter;
 use std::path::PathBuf;
 
-use crate::errors::{
-    EmptyOnClauseInOnUnimplemented, InvalidOnClauseInOnUnimplemented, NoValueInOnUnimplemented,
-};
-
-use crate::traits::error_reporting::type_err_ctxt_ext::InferCtxtPrivExt;
-
 /// The symbols which are always allowed in a format string
 static ALLOWED_FORMAT_SYMBOLS: &[Symbol] = &[
     kw::SelfUpper,

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

@@ -1073,7 +1073,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             // mismatched, then we have a totally different error to report.
             if self.enter_forall(found_args, |found_args| {
                 self.enter_forall(expected_args, |expected_args| {
-                    !self.can_sub(obligation.param_env, expected_args, found_args)
+                    !self.can_eq(obligation.param_env, expected_args, found_args)
                 })
             }) {
                 return None;

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

@@ -18,7 +18,7 @@ use super::{
     TraitQueryMode,
 };
 
-use crate::infer::{InferCtxt, InferOk, TypeFreshener};
+use crate::infer::{InferCtxt, InferCtxtExt, InferOk, TypeFreshener};
 use crate::solve::InferCtxtSelectExt as _;
 use crate::traits::error_reporting::TypeErrCtxtExt;
 use crate::traits::normalize::normalize_with_depth;

tests/ui/generic-associated-types/assume-gat-normalization-for-nested-goals.next.stderr

@@ -1,4 +1,4 @@
-error[E0277]: the trait bound `i32: Baz<Self>` is not satisfied
+error[E0277]: the trait bound `<Self as Foo>::Bar<()>: Eq<i32>` is not satisfied
   --> $DIR/assume-gat-normalization-for-nested-goals.rs:9:30
    |
 LL |     type Bar<T>: Baz<Self> = i32;

tests/ui/impl-trait/nested_impl_trait.rs

@@ -5,7 +5,7 @@ fn fine(x: impl Into<u32>) -> impl Into<u32> { x }
 
 fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
 //~^ ERROR nested `impl Trait` is not allowed
-//~| ERROR the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
+//~| ERROR the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
 
 fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
 //~^ ERROR nested `impl Trait` is not allowed
@@ -18,7 +18,7 @@ struct X;
 impl X {
     fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
     //~^ ERROR nested `impl Trait` is not allowed
-    //~| ERROR the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
+    //~| ERROR the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
 }
 
 fn allowed_in_assoc_type() -> impl Iterator<Item=impl Fn()> {

tests/ui/impl-trait/nested_impl_trait.stderr

@@ -42,7 +42,7 @@ LL | fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
    |
    = note: `impl Trait` is only allowed in arguments and return types of functions and methods
 
-error[E0277]: the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
+error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
   --> $DIR/nested_impl_trait.rs:6:46
    |
 LL | fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
@@ -51,7 +51,7 @@ LL | fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
    = help: the trait `Into<U>` is implemented for `T`
    = note: required for `impl Into<u32>` to implement `Into<impl Debug>`
 
-error[E0277]: the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
+error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
   --> $DIR/nested_impl_trait.rs:19:34
    |
 LL |     fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }

tests/ui/traits/next-solver/auto-with-drop_tracking_mir.fail.stderr

@@ -17,10 +17,6 @@ note: required by a bound in `is_send`
    |
 LL |     fn is_send(_: impl Send) {}
    |                        ^^^^ required by this bound in `is_send`
-help: consider dereferencing here
-   |
-LL |     is_send(*foo());
-   |             +
 
 error: aborting due to 1 previous error
 

tests/ui/type-alias-impl-trait/method_resolution3.current.stderr

@@ -8,7 +8,7 @@ LL |     fn bar(self: Bar<u32>) {
    = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 error[E0307]: invalid `self` parameter type: `&Bar<u32>`
-  --> $DIR/method_resolution3.rs:21:18
+  --> $DIR/method_resolution3.rs:20:18
    |
 LL |     fn baz(self: &Bar<u32>) {
    |                  ^^^^^^^^^

tests/ui/type-alias-impl-trait/method_resolution3.next.stderr

@@ -1,15 +1,21 @@
-error[E0271]: type mismatch resolving `Foo == u32`
+error[E0307]: invalid `self` parameter type: `Bar<u32>`
   --> $DIR/method_resolution3.rs:16:18
    |
 LL |     fn bar(self: Bar<u32>) {
-   |                  ^^^^^^^^ types differ
+   |                  ^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
-error[E0271]: type mismatch resolving `Foo == u32`
+error[E0307]: invalid `self` parameter type: `&Bar<u32>`
-  --> $DIR/method_resolution3.rs:21:18
+  --> $DIR/method_resolution3.rs:20:18
    |
 LL |     fn baz(self: &Bar<u32>) {
-   |                  ^^^^^^^^^ types differ
+   |                  ^^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+For more information about this error, try `rustc --explain E0307`.

tests/ui/type-alias-impl-trait/method_resolution3.rs

@@ -14,13 +14,11 @@ struct Bar<T>(T);
 
 impl Bar<Foo> {
     fn bar(self: Bar<u32>) {
-        //[current]~^ ERROR: invalid `self` parameter
+        //~^ ERROR: invalid `self` parameter
-        //[next]~^^ ERROR: type mismatch resolving `Foo == u32`
         self.foo()
     }
     fn baz(self: &Bar<u32>) {
-        //[current]~^ ERROR: invalid `self` parameter
+        //~^ ERROR: invalid `self` parameter
-        //[next]~^^ ERROR: type mismatch resolving `Foo == u32`
         self.foo()
     }
 }

tests/ui/type-alias-impl-trait/method_resolution4.current.stderr

@@ -8,7 +8,7 @@ LL |     fn foo(self: Bar<Foo>) {
    = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 error[E0307]: invalid `self` parameter type: `&Bar<Foo>`
-  --> $DIR/method_resolution4.rs:32:20
+  --> $DIR/method_resolution4.rs:31:20
    |
 LL |     fn foomp(self: &Bar<Foo>) {
    |                    ^^^^^^^^^

tests/ui/type-alias-impl-trait/method_resolution4.next.stderr

@@ -1,15 +1,21 @@
-error[E0271]: type mismatch resolving `u32 == Foo`
+error[E0307]: invalid `self` parameter type: `Bar<Foo>`
   --> $DIR/method_resolution4.rs:27:18
    |
 LL |     fn foo(self: Bar<Foo>) {
-   |                  ^^^^^^^^ types differ
+   |                  ^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
-error[E0271]: type mismatch resolving `u32 == Foo`
+error[E0307]: invalid `self` parameter type: `&Bar<Foo>`
-  --> $DIR/method_resolution4.rs:32:20
+  --> $DIR/method_resolution4.rs:31:20
    |
 LL |     fn foomp(self: &Bar<Foo>) {
-   |                    ^^^^^^^^^ types differ
+   |                    ^^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+For more information about this error, try `rustc --explain E0307`.

tests/ui/type-alias-impl-trait/method_resolution4.rs

@@ -25,13 +25,11 @@ impl Bar<Foo> {
 
 impl Bar<u32> {
     fn foo(self: Bar<Foo>) {
-        //[current]~^ ERROR: invalid `self` parameter
+        //~^ ERROR: invalid `self` parameter
-        //[next]~^^ ERROR: type mismatch resolving `u32 == Foo`
         self.bar()
     }
     fn foomp(self: &Bar<Foo>) {
-        //[current]~^ ERROR: invalid `self` parameter
+        //~^ ERROR: invalid `self` parameter
-        //[next]~^^ ERROR: type mismatch resolving `u32 == Foo`
         self.bar()
     }
 }