Check ADT fields for copy implementations considering regions

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -7,13 +7,15 @@ use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::ItemKind;
-use rustc_infer::infer;
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
 use rustc_infer::infer::TyCtxtInferExt;
+use rustc_infer::infer::{self, RegionResolutionError};
 use rustc_middle::ty::adjustment::CoerceUnsizedInfo;
 use rustc_middle::ty::{self, suggest_constraining_type_params, Ty, TyCtxt, TypeVisitable};
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
-use rustc_trait_selection::traits::misc::{can_type_implement_copy, CopyImplementationError};
+use rustc_trait_selection::traits::misc::{
+    type_allowed_to_implement_copy, CopyImplementationError, InfringingFieldsReason,
+};
 use rustc_trait_selection::traits::predicate_for_trait_def;
 use rustc_trait_selection::traits::{self, ObligationCause};
 use std::collections::BTreeMap;
@@ -82,7 +84,7 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
     };
 
     let cause = traits::ObligationCause::misc(span, impl_hir_id);
-    match can_type_implement_copy(tcx, param_env, self_type, cause) {
+    match type_allowed_to_implement_copy(tcx, param_env, self_type, cause) {
         Ok(()) => {}
         Err(CopyImplementationError::InfrigingFields(fields)) => {
             let mut err = struct_span_err!(
@@ -97,50 +99,70 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
             let mut errors: BTreeMap<_, Vec<_>> = Default::default();
             let mut bounds = vec![];
 
-            for (field, ty) in fields {
+            for (field, ty, reason) in fields {
                 let field_span = tcx.def_span(field.did);
-                let field_ty_span = match tcx.hir().get_if_local(field.did) {
-                    Some(hir::Node::Field(field_def)) => field_def.ty.span,
-                    _ => field_span,
-                };
                 err.span_label(field_span, "this field does not implement `Copy`");
-                // Spin up a new FulfillmentContext, so we can get the _precise_ reason
-                // why this field does not implement Copy. This is useful because sometimes
-                // it is not immediately clear why Copy is not implemented for a field, since
-                // all we point at is the field itself.
-                let infcx = tcx.infer_ctxt().ignoring_regions().build();
-                for error in traits::fully_solve_bound(
-                    &infcx,
-                    traits::ObligationCause::dummy_with_span(field_ty_span),
-                    param_env,
-                    ty,
-                    tcx.require_lang_item(LangItem::Copy, Some(span)),
-                ) {
-                    let error_predicate = error.obligation.predicate;
-                    // Only note if it's not the root obligation, otherwise it's trivial and
-                    // should be self-explanatory (i.e. a field literally doesn't implement Copy).
-
-                    // FIXME: This error could be more descriptive, especially if the error_predicate
-                    // contains a foreign type or if it's a deeply nested type...
-                    if error_predicate != error.root_obligation.predicate {
-                        errors
-                            .entry((ty.to_string(), error_predicate.to_string()))
-                            .or_default()
-                            .push(error.obligation.cause.span);
+
+                match reason {
+                    InfringingFieldsReason::Fulfill(fulfillment_errors) => {
+                        for error in fulfillment_errors {
+                            let error_predicate = error.obligation.predicate;
+                            // Only note if it's not the root obligation, otherwise it's trivial and
+                            // should be self-explanatory (i.e. a field literally doesn't implement Copy).
+
+                            // FIXME: This error could be more descriptive, especially if the error_predicate
+                            // contains a foreign type or if it's a deeply nested type...
+                            if error_predicate != error.root_obligation.predicate {
+                                errors
+                                    .entry((ty.to_string(), error_predicate.to_string()))
+                                    .or_default()
+                                    .push(error.obligation.cause.span);
+                            }
+                            if let ty::PredicateKind::Clause(ty::Clause::Trait(
+                                ty::TraitPredicate {
+                                    trait_ref,
+                                    polarity: ty::ImplPolarity::Positive,
+                                    ..
+                                },
+                            )) = error_predicate.kind().skip_binder()
+                            {
+                                let ty = trait_ref.self_ty();
+                                if let ty::Param(_) = ty.kind() {
+                                    bounds.push((
+                                        format!("{ty}"),
+                                        trait_ref.print_only_trait_path().to_string(),
+                                        Some(trait_ref.def_id),
+                                    ));
+                                }
+                            }
+                        }
                     }
-                    if let ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate {
-                        trait_ref,
-                        polarity: ty::ImplPolarity::Positive,
-                        ..
-                    })) = error_predicate.kind().skip_binder()
-                    {
-                        let ty = trait_ref.self_ty();
-                        if let ty::Param(_) = ty.kind() {
-                            bounds.push((
-                                format!("{ty}"),
-                                trait_ref.print_only_trait_path().to_string(),
-                                Some(trait_ref.def_id),
-                            ));
+                    InfringingFieldsReason::Regions(region_errors) => {
+                        for error in region_errors {
+                            let ty = ty.to_string();
+                            match error {
+                                RegionResolutionError::ConcreteFailure(origin, a, b) => {
+                                    let predicate = format!("{b}: {a}");
+                                    errors
+                                        .entry((ty.clone(), predicate.clone()))
+                                        .or_default()
+                                        .push(origin.span());
+                                    if let ty::RegionKind::ReEarlyBound(ebr) = *b && ebr.has_name() {
+                                        bounds.push((b.to_string(), a.to_string(), None));
+                                    }
+                                }
+                                RegionResolutionError::GenericBoundFailure(origin, a, b) => {
+                                    let predicate = format!("{a}: {b}");
+                                    errors
+                                        .entry((ty.clone(), predicate.clone()))
+                                        .or_default()
+                                        .push(origin.span());
+                                    if let infer::region_constraints::GenericKind::Param(_) = a {
+                                        bounds.push((a.to_string(), b.to_string(), None));
+                                    }
+                                }
+                                _ => continue,
+                            }
                         }
                     }
                 }

compiler/rustc_lint/src/builtin.rs

@@ -72,7 +72,7 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{BytePos, InnerSpan, Span};
 use rustc_target::abi::{Abi, VariantIdx};
 use rustc_trait_selection::infer::{InferCtxtExt, TyCtxtInferExt};
-use rustc_trait_selection::traits::{self, misc::can_type_implement_copy, EvaluationResult};
+use rustc_trait_selection::traits::{self, misc::type_allowed_to_implement_copy};
 
 use crate::nonstandard_style::{method_context, MethodLateContext};
 
@@ -709,12 +709,14 @@ impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
 
         // We shouldn't recommend implementing `Copy` on stateful things,
         // such as iterators.
-        if let Some(iter_trait) = cx.tcx.get_diagnostic_item(sym::Iterator) {
-            if cx.tcx.infer_ctxt().build().type_implements_trait(iter_trait, [ty], param_env)
-                == EvaluationResult::EvaluatedToOk
-            {
-                return;
-            }
+        if let Some(iter_trait) = cx.tcx.get_diagnostic_item(sym::Iterator)
+            && cx.tcx
+                .infer_ctxt()
+                .build()
+                .type_implements_trait(iter_trait, [ty], param_env)
+                .must_apply_modulo_regions()
+        {
+            return;
         }
 
         // Default value of clippy::trivially_copy_pass_by_ref
@@ -726,7 +728,7 @@ impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
             }
         }
 
-        if can_type_implement_copy(
+        if type_allowed_to_implement_copy(
             cx.tcx,
             param_env,
             ty,

compiler/rustc_trait_selection/src/traits/misc.rs

@@ -1,29 +1,36 @@
 //! Miscellaneous type-system utilities that are too small to deserve their own modules.
 
-use crate::infer::InferCtxtExt as _;
 use crate::traits::{self, ObligationCause};
 
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
-use rustc_infer::infer::TyCtxtInferExt;
+use rustc_infer::infer::{RegionResolutionError, TyCtxtInferExt};
+use rustc_infer::{infer::outlives::env::OutlivesEnvironment, traits::FulfillmentError};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
 
-use crate::traits::error_reporting::TypeErrCtxtExt;
+use super::outlives_bounds::InferCtxtExt;
 
-#[derive(Clone)]
 pub enum CopyImplementationError<'tcx> {
-    InfrigingFields(Vec<(&'tcx ty::FieldDef, Ty<'tcx>)>),
+    InfrigingFields(Vec<(&'tcx ty::FieldDef, Ty<'tcx>, InfringingFieldsReason<'tcx>)>),
     NotAnAdt,
     HasDestructor,
 }
 
-pub fn can_type_implement_copy<'tcx>(
+pub enum InfringingFieldsReason<'tcx> {
+    Fulfill(Vec<FulfillmentError<'tcx>>),
+    Regions(Vec<RegionResolutionError<'tcx>>),
+}
+
+/// Checks that the fields of the type (an ADT) all implement copy.
+///
+/// If fields don't implement copy, return an error containing a list of
+/// those violating fields. If it's not an ADT, returns `Err(NotAnAdt)`.
+pub fn type_allowed_to_implement_copy<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     self_type: Ty<'tcx>,
     parent_cause: ObligationCause<'tcx>,
 ) -> Result<(), CopyImplementationError<'tcx>> {
-    // FIXME: (@jroesch) float this code up
-    let infcx = tcx.infer_ctxt().build();
     let (adt, substs) = match self_type.kind() {
         // These types used to have a builtin impl.
         // Now libcore provides that impl.
@@ -42,42 +49,82 @@ pub fn can_type_implement_copy<'tcx>(
         _ => return Err(CopyImplementationError::NotAnAdt),
     };
 
+    let copy_def_id = tcx.require_lang_item(hir::LangItem::Copy, Some(parent_cause.span));
+
     let mut infringing = Vec::new();
     for variant in adt.variants() {
         for field in &variant.fields {
-            let ty = field.ty(tcx, substs);
-            if ty.references_error() {
+            // Do this per-field to get better error messages.
+            let infcx = tcx.infer_ctxt().build();
+            let ocx = traits::ObligationCtxt::new(&infcx);
+
+            let unnormalized_ty = field.ty(tcx, substs);
+            if unnormalized_ty.references_error() {
                 continue;
             }
-            let span = tcx.def_span(field.did);
+
+            let field_span = tcx.def_span(field.did);
+            let field_ty_span = match tcx.hir().get_if_local(field.did) {
+                Some(hir::Node::Field(field_def)) => field_def.ty.span,
+                _ => field_span,
+            };
+
             // FIXME(compiler-errors): This gives us better spans for bad
             // projection types like in issue-50480.
             // If the ADT has substs, point to the cause we are given.
             // If it does not, then this field probably doesn't normalize
             // to begin with, and point to the bad field's span instead.
-            let cause = if field
+            let normalization_cause = if field
                 .ty(tcx, traits::InternalSubsts::identity_for_item(tcx, adt.did()))
                 .has_non_region_param()
             {
                 parent_cause.clone()
             } else {
-                ObligationCause::dummy_with_span(span)
-            };
-            match traits::fully_normalize(&infcx, cause, param_env, ty) {
-                Ok(ty) => {
-                    if !infcx.type_is_copy_modulo_regions(param_env, ty, span) {
-                        infringing.push((field, ty));
-                    }
-                }
-                Err(errors) => {
-                    infcx.err_ctxt().report_fulfillment_errors(&errors, None);
-                }
+                ObligationCause::dummy_with_span(field_ty_span)
             };
+            let ty = ocx.normalize(&normalization_cause, param_env, unnormalized_ty);
+            let normalization_errors = ocx.select_where_possible();
+            if !normalization_errors.is_empty() {
+                tcx.sess.delay_span_bug(field_span, format!("couldn't normalize struct field `{unnormalized_ty}` when checking Copy implementation"));
+                continue;
+            }
+
+            ocx.register_bound(
+                ObligationCause::dummy_with_span(field_ty_span),
+                param_env,
+                ty,
+                copy_def_id,
+            );
+            let errors = ocx.select_all_or_error();
+            if !errors.is_empty() {
+                infringing.push((field, ty, InfringingFieldsReason::Fulfill(errors)));
+            }
+
+            // Check regions assuming the self type of the impl is WF
+            let outlives_env = OutlivesEnvironment::with_bounds(
+                param_env,
+                Some(&infcx),
+                infcx.implied_bounds_tys(
+                    param_env,
+                    parent_cause.body_id,
+                    FxIndexSet::from_iter([self_type]),
+                ),
+            );
+            infcx.process_registered_region_obligations(
+                outlives_env.region_bound_pairs(),
+                param_env,
+            );
+            let errors = infcx.resolve_regions(&outlives_env);
+            if !errors.is_empty() {
+                infringing.push((field, ty, InfringingFieldsReason::Regions(errors)));
+            }
         }
     }
+
     if !infringing.is_empty() {
         return Err(CopyImplementationError::InfrigingFields(infringing));
     }
+
     if adt.has_dtor(tcx) {
         return Err(CopyImplementationError::HasDestructor);
     }

src/tools/clippy/clippy_lints/src/needless_pass_by_value.rs

@@ -24,7 +24,7 @@ use rustc_span::symbol::kw;
 use rustc_span::{sym, Span};
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits;
-use rustc_trait_selection::traits::misc::can_type_implement_copy;
+use rustc_trait_selection::traits::misc::type_allowed_to_implement_copy;
 use std::borrow::Cow;
 
 declare_clippy_lint! {
@@ -200,7 +200,7 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessPassByValue {
                     let sugg = |diag: &mut Diagnostic| {
                         if let ty::Adt(def, ..) = ty.kind() {
                             if let Some(span) = cx.tcx.hir().span_if_local(def.did()) {
-                                if can_type_implement_copy(
+                                if type_allowed_to_implement_copy(
                                     cx.tcx,
                                     cx.param_env,
                                     ty,

tests/ui/traits/copy-impl-cannot-normalize.stderr

@@ -4,6 +4,16 @@ error[E0277]: the trait bound `T: TraitFoo` is not satisfied
 LL | impl<T> Copy for Foo<T> {}
    |                  ^^^^^^ the trait `TraitFoo` is not implemented for `T`
    |
+note: required for `Foo<T>` to implement `Clone`
+  --> $DIR/copy-impl-cannot-normalize.rs:12:9
+   |
+LL | impl<T> Clone for Foo<T>
+   |         ^^^^^     ^^^^^^
+LL | where
+LL |     T: TraitFoo,
+   |        -------- unsatisfied trait bound introduced here
+note: required by a bound in `Copy`
+  --> $SRC_DIR/core/src/marker.rs:LL:COL
 help: consider restricting type parameter `T`
    |
 LL | impl<T: TraitFoo> Copy for Foo<T> {}

tests/ui/traits/copy-is-not-modulo-regions.not_static.stderr

@@ -0,0 +1,22 @@
+error[E0204]: the trait `Copy` may not be implemented for this type
+  --> $DIR/copy-is-not-modulo-regions.rs:13:21
+   |
+LL | struct Bar<'lt>(Foo<'lt>);
+   |                 -------- this field does not implement `Copy`
+...
+LL | impl<'any> Copy for Bar<'any> {}
+   |                     ^^^^^^^^^
+   |
+note: the `Copy` impl for `Foo<'any>` requires that `'any: 'static`
+  --> $DIR/copy-is-not-modulo-regions.rs:10:17
+   |
+LL | struct Bar<'lt>(Foo<'lt>);
+   |                 ^^^^^^^^
+help: consider restricting type parameter `'any`
+   |
+LL | impl<'any: 'static> Copy for Bar<'any> {}
+   |          +++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0204`.

tests/ui/traits/copy-is-not-modulo-regions.rs

@@ -0,0 +1,19 @@
+// revisions: not_static yes_static
+//[yes_static] check-pass
+
+#[derive(Clone)]
+struct Foo<'lt>(&'lt ());
+
+impl Copy for Foo<'static> {}
+
+#[derive(Clone)]
+struct Bar<'lt>(Foo<'lt>);
+
+#[cfg(not_static)]
+impl<'any> Copy for Bar<'any> {}
+//[not_static]~^ the trait `Copy` may not be implemented for this type
+
+#[cfg(yes_static)]
+impl<'any> Copy for Bar<'static> {}
+
+fn main() {}