Auto merge of rust-lang#131797 - matthiaskrgr:rollup-lzpze2k, r=matth…

…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#130989 (Don't check unsize goal in MIR validation when opaques remain)
 - rust-lang#131657 (Rustfmt `for<'a> async` correctly)
 - rust-lang#131691 (Delay ambiguous intra-doc link resolution after `Cache` has been populated)
 - rust-lang#131730 (Refactor some `core::fmt` macros)
 - rust-lang#131751 (Rename `can_coerce` to `may_coerce`, and then structurally resolve correctly in the probe)
 - rust-lang#131753 (Unify `secondary_span` and `swap_secondary_and_primary` args in `note_type_err`)
 - rust-lang#131776 (Emscripten: Xfail backtrace ui tests)
 - rust-lang#131777 (Fix trivially_copy_pass_by_ref in stable_mir)
 - rust-lang#131778 (Fix needless_lifetimes in stable_mir)

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -592,14 +592,13 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                 &cause,
                 hir.get_if_local(impl_m.def_id)
                     .and_then(|node| node.fn_decl())
-                    .map(|decl| (decl.output.span(), Cow::from("return type in trait"))),
+                    .map(|decl| (decl.output.span(), Cow::from("return type in trait"), false)),
                 Some(infer::ValuePairs::Terms(ExpectedFound {
                     expected: trait_return_ty.into(),
                     found: impl_return_ty.into(),
                 })),
                 terr,
                 false,
-                false,
             );
             return Err(diag.emit());
         }
@@ -1018,14 +1017,13 @@ fn report_trait_method_mismatch<'tcx>(
     infcx.err_ctxt().note_type_err(
         &mut diag,
         &cause,
-        trait_err_span.map(|sp| (sp, Cow::from("type in trait"))),
+        trait_err_span.map(|sp| (sp, Cow::from("type in trait"), false)),
         Some(infer::ValuePairs::PolySigs(ExpectedFound {
             expected: ty::Binder::dummy(trait_sig),
             found: ty::Binder::dummy(impl_sig),
         })),
         terr,
         false,
-        false,
     );
 
     diag.emit()
@@ -1825,14 +1823,13 @@ fn compare_const_predicate_entailment<'tcx>(
         infcx.err_ctxt().note_type_err(
             &mut diag,
             &cause,
-            trait_c_span.map(|span| (span, Cow::from("type in trait"))),
+            trait_c_span.map(|span| (span, Cow::from("type in trait"), false)),
             Some(infer::ValuePairs::Terms(ExpectedFound {
                 expected: trait_ty.into(),
                 found: impl_ty.into(),
             })),
             terr,
             false,
-            false,
         );
         return Err(diag.emit());
     };

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -652,7 +652,6 @@ pub fn check_function_signature<'tcx>(
                 })),
                 err,
                 false,
-                false,
             );
             return Err(diag.emit());
         }

compiler/rustc_hir_typeck/src/_match.rs

@@ -235,8 +235,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             Some(ret_coercion) => {
                 let ret_ty = ret_coercion.borrow().expected_ty();
                 let ret_ty = self.infcx.shallow_resolve(ret_ty);
-                self.can_coerce(arm_ty, ret_ty)
-                    && prior_arm.is_none_or(|(_, ty, _)| self.can_coerce(ty, ret_ty))
+                self.may_coerce(arm_ty, ret_ty)
+                    && prior_arm.is_none_or(|(_, ty, _)| self.may_coerce(ty, ret_ty))
                     // The match arms need to unify for the case of `impl Trait`.
                     && !matches!(ret_ty.kind(), ty::Alias(ty::Opaque, ..))
             }

compiler/rustc_hir_typeck/src/cast.rs

@@ -409,7 +409,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
                 let mut sugg_mutref = false;
                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
                     if let ty::RawPtr(expr_ty, _) = *self.expr_ty.kind()
-                        && fcx.can_coerce(
+                        && fcx.may_coerce(
                             Ty::new_ref(fcx.tcx, fcx.tcx.lifetimes.re_erased, expr_ty, mutbl),
                             self.cast_ty,
                         )
@@ -418,22 +418,22 @@ impl<'a, 'tcx> CastCheck<'tcx> {
                     } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
                         && expr_mutbl == Mutability::Not
                         && mutbl == Mutability::Mut
-                        && fcx.can_coerce(Ty::new_mut_ref(fcx.tcx, expr_reg, expr_ty), self.cast_ty)
+                        && fcx.may_coerce(Ty::new_mut_ref(fcx.tcx, expr_reg, expr_ty), self.cast_ty)
                     {
                         sugg_mutref = true;
                     }
 
                     if !sugg_mutref
                         && sugg == None
-                        && fcx.can_coerce(
+                        && fcx.may_coerce(
                             Ty::new_ref(fcx.tcx, reg, self.expr_ty, mutbl),
                             self.cast_ty,
                         )
                     {
                         sugg = Some((format!("&{}", mutbl.prefix_str()), false));
                     }
                 } else if let ty::RawPtr(_, mutbl) = *self.cast_ty.kind()
-                    && fcx.can_coerce(
+                    && fcx.may_coerce(
                         Ty::new_ref(fcx.tcx, fcx.tcx.lifetimes.re_erased, self.expr_ty, mutbl),
                         self.cast_ty,
                     )

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1084,24 +1084,42 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         })
     }
 
-    /// Same as `coerce()`, but without side-effects.
+    /// Probe whether `expr_ty` can be coerced to `target_ty`. This has no side-effects,
+    /// and may return false positives if types are not yet fully constrained by inference.
     ///
-    /// Returns false if the coercion creates any obligations that result in
-    /// errors.
-    pub(crate) fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
-        // FIXME(-Znext-solver): We need to structurally resolve both types here.
-        let source = self.resolve_vars_with_obligations(expr_ty);
-        debug!("coercion::can_with_predicates({:?} -> {:?})", source, target);
-
+    /// Returns false if the coercion is not possible, or if the coercion creates any
+    /// sub-obligations that result in errors.
+    ///
+    /// This should only be used for diagnostics.
+    pub(crate) fn may_coerce(&self, expr_ty: Ty<'tcx>, target_ty: Ty<'tcx>) -> bool {
         let cause = self.cause(DUMMY_SP, ObligationCauseCode::ExprAssignable);
         // We don't ever need two-phase here since we throw out the result of the coercion.
         // We also just always set `coerce_never` to true, since this is a heuristic.
-        let coerce = Coerce::new(self, cause, AllowTwoPhase::No, true);
+        let coerce = Coerce::new(self, cause.clone(), AllowTwoPhase::No, true);
         self.probe(|_| {
-            let Ok(ok) = coerce.coerce(source, target) else {
+            // Make sure to structurally resolve the types, since we use
+            // the `TyKind`s heavily in coercion.
+            let ocx = ObligationCtxt::new(self);
+            let structurally_resolve = |ty| {
+                let ty = self.shallow_resolve(ty);
+                if self.next_trait_solver()
+                    && let ty::Alias(..) = ty.kind()
+                {
+                    ocx.structurally_normalize(&cause, self.param_env, ty)
+                } else {
+                    Ok(ty)
+                }
+            };
+            let Ok(expr_ty) = structurally_resolve(expr_ty) else {
+                return false;
+            };
+            let Ok(target_ty) = structurally_resolve(target_ty) else {
+                return false;
+            };
+
+            let Ok(ok) = coerce.coerce(expr_ty, target_ty) else {
                 return false;
             };
-            let ocx = ObligationCtxt::new(self);
             ocx.register_obligations(ok.obligations);
             ocx.select_where_possible().is_empty()
         })
@@ -1370,7 +1388,7 @@ pub fn can_coerce<'tcx>(
 ) -> bool {
     let root_ctxt = crate::typeck_root_ctxt::TypeckRootCtxt::new(tcx, body_id);
     let fn_ctxt = FnCtxt::new(&root_ctxt, param_env, body_id);
-    fn_ctxt.can_coerce(ty, output_ty)
+    fn_ctxt.may_coerce(ty, output_ty)
 }
 
 /// CoerceMany encapsulates the pattern you should use when you have

compiler/rustc_hir_typeck/src/expr.rs

@@ -1330,9 +1330,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let refs_can_coerce = |lhs: Ty<'tcx>, rhs: Ty<'tcx>| {
                 let lhs = Ty::new_imm_ref(self.tcx, self.tcx.lifetimes.re_erased, lhs.peel_refs());
                 let rhs = Ty::new_imm_ref(self.tcx, self.tcx.lifetimes.re_erased, rhs.peel_refs());
-                self.can_coerce(rhs, lhs)
+                self.may_coerce(rhs, lhs)
             };
-            let (applicability, eq) = if self.can_coerce(rhs_ty, lhs_ty) {
+            let (applicability, eq) = if self.may_coerce(rhs_ty, lhs_ty) {
                 (Applicability::MachineApplicable, true)
             } else if refs_can_coerce(rhs_ty, lhs_ty) {
                 // The lhs and rhs are likely missing some references in either side. Subsequent
@@ -1349,7 +1349,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 let actual_lhs_ty = self.check_expr(rhs_expr);
                 (
                     Applicability::MaybeIncorrect,
-                    self.can_coerce(rhs_ty, actual_lhs_ty)
+                    self.may_coerce(rhs_ty, actual_lhs_ty)
                         || refs_can_coerce(rhs_ty, actual_lhs_ty),
                 )
             } else if let ExprKind::Binary(
@@ -1363,7 +1363,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 let actual_rhs_ty = self.check_expr(lhs_expr);
                 (
                     Applicability::MaybeIncorrect,
-                    self.can_coerce(actual_rhs_ty, lhs_ty)
+                    self.may_coerce(actual_rhs_ty, lhs_ty)
                         || refs_can_coerce(actual_rhs_ty, lhs_ty),
                 )
             } else {
@@ -1414,7 +1414,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self.param_env,
                     )
                     .may_apply();
-                if lhs_deref_ty_is_sized && self.can_coerce(rhs_ty, lhs_deref_ty) {
+                if lhs_deref_ty_is_sized && self.may_coerce(rhs_ty, lhs_deref_ty) {
                     err.span_suggestion_verbose(
                         lhs.span.shrink_to_lo(),
                         "consider dereferencing here to assign to the mutably borrowed value",

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -658,7 +658,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 && fn_sig.inputs()[1..]
                     .iter()
                     .zip(input_types.iter())
-                    .all(|(expected, found)| self.can_coerce(*expected, *found))
+                    .all(|(expected, found)| self.may_coerce(*expected, *found))
                 && fn_sig.inputs()[1..].len() == input_types.len()
             {
                 err.span_suggestion_verbose(
@@ -722,7 +722,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             let expectation = Expectation::rvalue_hint(self, expected_input_ty);
             let coerced_ty = expectation.only_has_type(self).unwrap_or(formal_input_ty);
-            let can_coerce = self.can_coerce(arg_ty, coerced_ty);
+            let can_coerce = self.may_coerce(arg_ty, coerced_ty);
             if !can_coerce {
                 return Compatibility::Incompatible(Some(ty::error::TypeError::Sorts(
                     ty::error::ExpectedFound::new(true, coerced_ty, arg_ty),
@@ -802,7 +802,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         provided_arg_tys.iter().map(|(ty, _)| *ty).skip(mismatch_idx + tys.len()),
                     ),
                 ) {
-                    if !self.can_coerce(provided_ty, *expected_ty) {
+                    if !self.may_coerce(provided_ty, *expected_ty) {
                         satisfied = false;
                         break;
                     }
@@ -1023,7 +1023,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 std::iter::zip(formal_and_expected_inputs.iter(), removed_arg_tys.iter()).all(
                     |((expected_ty, _), (provided_ty, _))| {
                         !provided_ty.references_error()
-                            && self.can_coerce(*provided_ty, *expected_ty)
+                            && self.may_coerce(*provided_ty, *expected_ty)
                     },
                 )
             };
@@ -1114,7 +1114,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 None,
                                 Some(trace.values),
                                 e,
-                                false,
                                 true,
                             );
                         }
@@ -2124,7 +2123,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                     let expr_ty = self.typeck_results.borrow().expr_ty(expr);
                                     let return_ty = fn_sig.output();
                                     if !matches!(expr.kind, hir::ExprKind::Ret(..))
-                                        && self.can_coerce(expr_ty, return_ty)
+                                        && self.may_coerce(expr_ty, return_ty)
                                     {
                                         found_semi = true;
                                     }