Set correct `ParamEnv` for `derive_partial_eq_without_eq`

4 files changed, 67 insertions, 14 deletions

diff --git a/clippy_lints/src/derive.rs b/clippy_lints/src/derive.rs
index fe99f4a8d55..99347ebadc6 100644
--- a/clippy_lints/src/derive.rs
+++ b/clippy_lints/src/derive.rs
@@ -1,16 +1,17 @@
 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then};
 use clippy_utils::paths;
-use clippy_utils::ty::{implements_trait, is_copy};
+use clippy_utils::ty::{implements_trait, implements_trait_with_env, is_copy};
 use clippy_utils::{is_lint_allowed, match_def_path};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_expr, walk_fn, walk_item, FnKind, Visitor};
 use rustc_hir::{
-    BlockCheckMode, BodyId, Expr, ExprKind, FnDecl, HirId, Impl, Item, ItemKind, TraitRef, UnsafeSource, Unsafety,
+    self as hir, BlockCheckMode, BodyId, Expr, ExprKind, FnDecl, HirId, Impl, Item, ItemKind, UnsafeSource, Unsafety,
 };
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::nested_filter;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::subst::GenericArg;
+use rustc_middle::ty::{self, BoundConstness, ImplPolarity, ParamEnv, PredicateKind, TraitPredicate, TraitRef, Ty};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
 use rustc_span::sym;
@@ -224,7 +225,7 @@ impl<'tcx> LateLintPass<'tcx> for Derive {
 fn check_hash_peq<'tcx>(
     cx: &LateContext<'tcx>,
     span: Span,
-    trait_ref: &TraitRef<'_>,
+    trait_ref: &hir::TraitRef<'_>,
     ty: Ty<'tcx>,
     hash_is_automatically_derived: bool,
 ) {
@@ -277,7 +278,7 @@ fn check_hash_peq<'tcx>(
 fn check_ord_partial_ord<'tcx>(
     cx: &LateContext<'tcx>,
     span: Span,
-    trait_ref: &TraitRef<'_>,
+    trait_ref: &hir::TraitRef<'_>,
     ty: Ty<'tcx>,
     ord_is_automatically_derived: bool,
 ) {
@@ -328,7 +329,7 @@ fn check_ord_partial_ord<'tcx>(
 }
 
 /// Implementation of the `EXPL_IMPL_CLONE_ON_COPY` lint.
-fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &TraitRef<'_>, ty: Ty<'tcx>) {
+fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &hir::TraitRef<'_>, ty: Ty<'tcx>) {
     let clone_id = match cx.tcx.lang_items().clone_trait() {
         Some(id) if trait_ref.trait_def_id() == Some(id) => id,
         _ => return,
@@ -378,7 +379,7 @@ fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &T
 fn check_unsafe_derive_deserialize<'tcx>(
     cx: &LateContext<'tcx>,
     item: &Item<'_>,
-    trait_ref: &TraitRef<'_>,
+    trait_ref: &hir::TraitRef<'_>,
     ty: Ty<'tcx>,
 ) {
     fn has_unsafe<'tcx>(cx: &LateContext<'tcx>, item: &'tcx Item<'_>) -> bool {
@@ -455,13 +456,41 @@ impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
 }
 
 /// Implementation of the `DERIVE_PARTIAL_EQ_WITHOUT_EQ` lint.
-fn check_partial_eq_without_eq<'tcx>(cx: &LateContext<'tcx>, span: Span, trait_ref: &TraitRef<'_>, ty: Ty<'tcx>) {
+fn check_partial_eq_without_eq<'tcx>(cx: &LateContext<'tcx>, span: Span, trait_ref: &hir::TraitRef<'_>, ty: Ty<'tcx>) {
     if_chain! {
         if let ty::Adt(adt, substs) = ty.kind();
         if let Some(eq_trait_def_id) = cx.tcx.get_diagnostic_item(sym::Eq);
+        if let Some(peq_trait_def_id) = cx.tcx.get_diagnostic_item(sym::PartialEq);
         if let Some(def_id) = trait_ref.trait_def_id();
         if cx.tcx.is_diagnostic_item(sym::PartialEq, def_id);
-        if !implements_trait(cx, ty, eq_trait_def_id, substs);
+        // New `ParamEnv` replacing `T: PartialEq` with `T: Eq`
+        let param_env = ParamEnv::new(
+            cx.tcx.mk_predicates(cx.param_env.caller_bounds().iter().map(|p| {
+                let kind = p.kind();
+                match kind.skip_binder() {
+                    PredicateKind::Trait(p)
+                        if p.trait_ref.def_id == peq_trait_def_id
+                            && p.trait_ref.substs.get(0) == p.trait_ref.substs.get(1)
+                            && matches!(p.trait_ref.self_ty().kind(), ty::Param(_))
+                            && p.constness == BoundConstness::NotConst
+                            && p.polarity == ImplPolarity::Positive =>
+                    {
+                        cx.tcx.mk_predicate(kind.rebind(PredicateKind::Trait(TraitPredicate {
+                            trait_ref: TraitRef::new(
+                                eq_trait_def_id,
+                                cx.tcx.mk_substs([GenericArg::from(p.trait_ref.self_ty())].into_iter()),
+                            ),
+                            constness: BoundConstness::NotConst,
+                            polarity: ImplPolarity::Positive,
+                        })))
+                    },
+                    _ => p,
+                }
+            })),
+            cx.param_env.reveal(),
+            cx.param_env.constness(),
+        );
+        if !implements_trait_with_env(cx.tcx, param_env, ty, eq_trait_def_id, substs);
         then {
             // If all of our fields implement `Eq`, we can implement `Eq` too
             for variant in adt.variants() {
diff --git a/clippy_utils/src/ty.rs b/clippy_utils/src/ty.rs
index 07d3d280763..203f33d3529 100644
--- a/clippy_utils/src/ty.rs
+++ b/clippy_utils/src/ty.rs
@@ -13,7 +13,8 @@ use rustc_lint::LateContext;
 use rustc_middle::mir::interpret::{ConstValue, Scalar};
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst};
 use rustc_middle::ty::{
-    self, AdtDef, Binder, FnSig, IntTy, Predicate, PredicateKind, Ty, TyCtxt, TypeFoldable, UintTy, VariantDiscr,
+    self, AdtDef, Binder, FnSig, IntTy, ParamEnv, Predicate, PredicateKind, Ty, TyCtxt, TypeFoldable, UintTy,
+    VariantDiscr,
 };
 use rustc_span::symbol::Ident;
 use rustc_span::{sym, Span, Symbol, DUMMY_SP};
@@ -152,17 +153,28 @@ pub fn implements_trait<'tcx>(
     trait_id: DefId,
     ty_params: &[GenericArg<'tcx>],
 ) -> bool {
+    implements_trait_with_env(cx.tcx, cx.param_env, ty, trait_id, ty_params)
+}
+
+/// Same as `implements_trait` but allows using a `ParamEnv` different from the lint context.
+pub fn implements_trait_with_env<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    param_env: ParamEnv<'tcx>,
+    ty: Ty<'tcx>,
+    trait_id: DefId,
+    ty_params: &[GenericArg<'tcx>],
+) -> bool {
     // Clippy shouldn't have infer types
     assert!(!ty.needs_infer());
 
-    let ty = cx.tcx.erase_regions(ty);
+    let ty = tcx.erase_regions(ty);
     if ty.has_escaping_bound_vars() {
         return false;
     }
-    let ty_params = cx.tcx.mk_substs(ty_params.iter());
-    cx.tcx.infer_ctxt().enter(|infcx| {
+    let ty_params = tcx.mk_substs(ty_params.iter());
+    tcx.infer_ctxt().enter(|infcx| {
         infcx
-            .type_implements_trait(trait_id, ty, ty_params, cx.param_env)
+            .type_implements_trait(trait_id, ty, ty_params, param_env)
             .must_apply_modulo_regions()
     })
 }
diff --git a/tests/ui/derive_partial_eq_without_eq.fixed b/tests/ui/derive_partial_eq_without_eq.fixed
index 7d4d1b3b649..012780258fc 100644
--- a/tests/ui/derive_partial_eq_without_eq.fixed
+++ b/tests/ui/derive_partial_eq_without_eq.fixed
@@ -95,4 +95,10 @@ enum EnumNotEq {
 #[derive(Debug, PartialEq, Eq, Clone)]
 struct RustFixWithOtherDerives;
 
+#[derive(PartialEq)]
+struct Generic<T>(T);
+
+#[derive(PartialEq, Eq)]
+struct GenericPhantom<T>(core::marker::PhantomData<T>);
+
 fn main() {}
diff --git a/tests/ui/derive_partial_eq_without_eq.rs b/tests/ui/derive_partial_eq_without_eq.rs
index ab4e1df1ca4..fc8285b0c6b 100644
--- a/tests/ui/derive_partial_eq_without_eq.rs
+++ b/tests/ui/derive_partial_eq_without_eq.rs
@@ -95,4 +95,10 @@ enum EnumNotEq {
 #[derive(Debug, PartialEq, Clone)]
 struct RustFixWithOtherDerives;
 
+#[derive(PartialEq)]
+struct Generic<T>(T);
+
+#[derive(PartialEq, Eq)]
+struct GenericPhantom<T>(core::marker::PhantomData<T>);
+
 fn main() {}