Auto merge of #118379 - compiler-errors:const-params-for-partialeq, r=fee1-dead

Fix `PartialEq` args when `#[const_trait]` is enabled

This is based off of your PR that enforces effects on all methods, so just see the last commits.

r? fee1-dead

8 files changed, 85 insertions, 91 deletions

diff --git a/compiler/rustc_hir_typeck/src/callee.rs b/compiler/rustc_hir_typeck/src/callee.rs
index 365170a6bbf..d3abe0d7e1a 100644
--- a/compiler/rustc_hir_typeck/src/callee.rs
+++ b/compiler/rustc_hir_typeck/src/callee.rs
@@ -6,9 +6,8 @@ use crate::errors;
 use rustc_ast::util::parser::PREC_POSTFIX;
 use rustc_errors::{Applicability, Diagnostic, ErrorGuaranteed, StashKey};
 use rustc_hir as hir;
-use rustc_hir::def::{self, CtorKind, DefKind, Namespace, Res};
+use rustc_hir::def::{self, CtorKind, Namespace, Res};
 use rustc_hir::def_id::DefId;
-use rustc_hir::HirId;
 use rustc_hir_analysis::autoderef::Autoderef;
 use rustc_infer::{
     infer,
@@ -373,7 +372,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> Ty<'tcx> {
         let (fn_sig, def_id) = match *callee_ty.kind() {
             ty::FnDef(def_id, args) => {
-                self.enforce_context_effects(call_expr.hir_id, call_expr.span, def_id, args);
+                self.enforce_context_effects(call_expr.span, def_id, args);
                 let fn_sig = self.tcx.fn_sig(def_id).instantiate(self.tcx, args);
 
                 // Unit testing: function items annotated with
@@ -770,7 +769,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     #[tracing::instrument(level = "debug", skip(self, span))]
     pub(super) fn enforce_context_effects(
         &self,
-        call_expr_hir: HirId,
         span: Span,
         callee_did: DefId,
         callee_args: GenericArgsRef<'tcx>,
@@ -781,38 +779,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let generics = tcx.generics_of(callee_did);
         let Some(host_effect_index) = generics.host_effect_index else { return };
 
-        // if the callee does have the param, we need to equate the param to some const
-        // value no matter whether the effects feature is enabled in the local crate,
-        // because inference will fail if we don't.
-        let mut host_always_on =
-            !tcx.features().effects || tcx.sess.opts.unstable_opts.unleash_the_miri_inside_of_you;
-
-        // Compute the constness required by the context.
-        let context = tcx.hir().enclosing_body_owner(call_expr_hir);
-        let const_context = tcx.hir().body_const_context(context);
-
-        let kind = tcx.def_kind(context.to_def_id());
-        debug_assert_ne!(kind, DefKind::ConstParam);
-
-        if tcx.has_attr(context.to_def_id(), sym::rustc_do_not_const_check) {
-            trace!("do not const check this context");
-            host_always_on = true;
-        }
-
-        let effect = match const_context {
-            _ if host_always_on => tcx.consts.true_,
-            Some(hir::ConstContext::Static(_) | hir::ConstContext::Const { .. }) => {
-                tcx.consts.false_
-            }
-            Some(hir::ConstContext::ConstFn) => {
-                let host_idx = tcx
-                    .generics_of(context)
-                    .host_effect_index
-                    .expect("ConstContext::Maybe must have host effect param");
-                ty::GenericArgs::identity_for_item(tcx, context).const_at(host_idx)
-            }
-            None => tcx.consts.true_,
-        };
+        let effect = tcx.expected_const_effect_param_for_body(self.body_id);
 
         trace!(?effect, ?generics, ?callee_args);
 
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index fae192e230c..23b9ac4139d 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -165,7 +165,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         span: Span,
         method: MethodCallee<'tcx>,
     ) {
-        self.enforce_context_effects(hir_id, span, method.def_id, method.args);
+        self.enforce_context_effects(span, method.def_id, method.args);
         self.write_resolution(hir_id, Ok((DefKind::AssocFn, method.def_id)));
         self.write_args(hir_id, method.args);
     }
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index 87c93afe540..f1720dc98e6 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -282,12 +282,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 span: provided_arg.span,
                             });
                         } else {
-                            self.enforce_context_effects(
-                                provided_arg.hir_id,
-                                provided_arg.span,
-                                def_id,
-                                args,
-                            )
+                            self.enforce_context_effects(provided_arg.span, def_id, args)
                         }
                     }
                 } else {
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index cbf1a9900d9..40d592ddef0 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -779,6 +779,57 @@ impl<'tcx> TyCtxt<'tcx> {
             // the language.
             || self.extern_crate(key.as_def_id()).is_some_and(|e| e.is_direct())
     }
+
+    pub fn expected_const_effect_param_for_body(self, def_id: LocalDefId) -> ty::Const<'tcx> {
+        // if the callee does have the param, we need to equate the param to some const
+        // value no matter whether the effects feature is enabled in the local crate,
+        // because inference will fail if we don't.
+        let mut host_always_on =
+            !self.features().effects || self.sess.opts.unstable_opts.unleash_the_miri_inside_of_you;
+
+        // Compute the constness required by the context.
+        let const_context = self.hir().body_const_context(def_id);
+
+        let kind = self.def_kind(def_id);
+        debug_assert_ne!(kind, DefKind::ConstParam);
+
+        if self.has_attr(def_id, sym::rustc_do_not_const_check) {
+            trace!("do not const check this context");
+            host_always_on = true;
+        }
+
+        match const_context {
+            _ if host_always_on => self.consts.true_,
+            Some(hir::ConstContext::Static(_) | hir::ConstContext::Const { .. }) => {
+                self.consts.false_
+            }
+            Some(hir::ConstContext::ConstFn) => {
+                let host_idx = self
+                    .generics_of(def_id)
+                    .host_effect_index
+                    .expect("ConstContext::Maybe must have host effect param");
+                ty::GenericArgs::identity_for_item(self, def_id).const_at(host_idx)
+            }
+            None => self.consts.true_,
+        }
+    }
+
+    /// Constructs generic args for an item, optionally appending a const effect param type
+    pub fn with_opt_const_effect_param(
+        self,
+        caller_def_id: LocalDefId,
+        callee_def_id: DefId,
+        args: impl IntoIterator<Item: Into<ty::GenericArg<'tcx>>>,
+    ) -> ty::GenericArgsRef<'tcx> {
+        let generics = self.generics_of(callee_def_id);
+        assert_eq!(generics.parent, None);
+
+        let opt_const_param = generics.host_effect_index.is_some().then(|| {
+            ty::GenericArg::from(self.expected_const_effect_param_for_body(caller_def_id))
+        });
+
+        self.mk_args_from_iter(args.into_iter().map(|arg| arg.into()).chain(opt_const_param))
+    }
 }
 
 struct OpaqueTypeExpander<'tcx> {
diff --git a/compiler/rustc_mir_build/src/build/matches/test.rs b/compiler/rustc_mir_build/src/build/matches/test.rs
index 2e7182f261e..642ac9b49c8 100644
--- a/compiler/rustc_mir_build/src/build/matches/test.rs
+++ b/compiler/rustc_mir_build/src/build/matches/test.rs
@@ -496,7 +496,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         }
 
         let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, Some(source_info.span));
-        let method = trait_method(self.tcx, eq_def_id, sym::eq, [ty, ty]);
+        let method = trait_method(
+            self.tcx,
+            eq_def_id,
+            sym::eq,
+            self.tcx.with_opt_const_effect_param(self.def_id, eq_def_id, [ty, ty]),
+        );
 
         let bool_ty = self.tcx.types.bool;
         let eq_result = self.temp(bool_ty, source_info.span);
diff --git a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
index c4bf2f23899..4e2c932d6c6 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
@@ -258,18 +258,26 @@ impl<'tcx> ConstToPat<'tcx> {
 
     #[instrument(level = "trace", skip(self), ret)]
     fn type_has_partial_eq_impl(&self, ty: Ty<'tcx>) -> bool {
+        let tcx = self.tcx();
         // double-check there even *is* a semantic `PartialEq` to dispatch to.
         //
         // (If there isn't, then we can safely issue a hard
         // error, because that's never worked, due to compiler
         // using `PartialEq::eq` in this scenario in the past.)
-        let tcx = self.tcx();
         let partial_eq_trait_id = tcx.require_lang_item(hir::LangItem::PartialEq, Some(self.span));
         let partial_eq_obligation = Obligation::new(
             tcx,
             ObligationCause::dummy(),
             self.param_env,
-            ty::TraitRef::new(tcx, partial_eq_trait_id, [ty, ty]),
+            ty::TraitRef::new(
+                tcx,
+                partial_eq_trait_id,
+                tcx.with_opt_const_effect_param(
+                    tcx.hir().enclosing_body_owner(self.id),
+                    partial_eq_trait_id,
+                    [ty, ty],
+                ),
+            ),
         );
 
         // This *could* accept a type that isn't actually `PartialEq`, because region bounds get
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs
index 67da5f9533c..ecf45c97dcd 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs
@@ -336,7 +336,7 @@ fn from_str(s: &str) -> Result<bool, ()> {
 }
 
 #[lang = "eq"]
-// FIXME #[const_trait]
+#[const_trait]
 trait PartialEq<Rhs: ?Sized = Self> {
     fn eq(&self, other: &Rhs) -> bool;
     fn ne(&self, other: &Rhs) -> bool {
@@ -344,6 +344,15 @@ trait PartialEq<Rhs: ?Sized = Self> {
     }
 }
 
+impl<A: ?Sized, B: ?Sized> const PartialEq<&B> for &A
+where
+    A: ~const PartialEq<B>,
+{
+    fn eq(&self, other: &&B) -> bool {
+        PartialEq::eq(*self, *other)
+    }
+}
+
 // FIXME(effects): again, this should not error without Rhs specified
 impl PartialEq<str> for str {
     fn eq(&self, other: &str) -> bool {
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr
index 19e6f6bffc6..461133e6c3e 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr
@@ -1,24 +1,5 @@
-warning: to use a constant of type `&str` in a pattern, the type must implement `PartialEq`
-  --> $DIR/minicore.rs:332:9
-   |
-LL |         "true" => Ok(true),
-   |         ^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #116122 <https://github.com/rust-lang/rust/issues/116122>
-   = note: `#[warn(const_patterns_without_partial_eq)]` on by default
-
-warning: to use a constant of type `&str` in a pattern, the type must implement `PartialEq`
-  --> $DIR/minicore.rs:333:9
-   |
-LL |         "false" => Ok(false),
-   |         ^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #116122 <https://github.com/rust-lang/rust/issues/116122>
-
 error[E0493]: destructor of `Self` cannot be evaluated at compile-time
-  --> $DIR/minicore.rs:494:9
+  --> $DIR/minicore.rs:503:9
    |
 LL |         *self = source.clone()
    |         ^^^^^
@@ -27,35 +8,13 @@ LL |         *self = source.clone()
    |         value is dropped here
 
 error[E0493]: destructor of `T` cannot be evaluated at compile-time
-  --> $DIR/minicore.rs:504:35
+  --> $DIR/minicore.rs:513:35
    |
 LL | const fn drop<T: ~const Destruct>(_: T) {}
    |                                   ^      - value is dropped here
    |                                   |
    |                                   the destructor for this type cannot be evaluated in constant functions
 
-error: aborting due to 2 previous errors; 2 warnings emitted
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0493`.
-Future incompatibility report: Future breakage diagnostic:
-warning: to use a constant of type `&str` in a pattern, the type must implement `PartialEq`
-  --> $DIR/minicore.rs:332:9
-   |
-LL |         "true" => Ok(true),
-   |         ^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #116122 <https://github.com/rust-lang/rust/issues/116122>
-   = note: `#[warn(const_patterns_without_partial_eq)]` on by default
-
-Future breakage diagnostic:
-warning: to use a constant of type `&str` in a pattern, the type must implement `PartialEq`
-  --> $DIR/minicore.rs:333:9
-   |
-LL |         "false" => Ok(false),
-   |         ^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #116122 <https://github.com/rust-lang/rust/issues/116122>
-   = note: `#[warn(const_patterns_without_partial_eq)]` on by default
-