lint implied_bounds_from_trait_impl

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -113,10 +113,43 @@ pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
         return;
     }
 
-    let implied_bounds = infcx.implied_bounds_tys_v2(param_env, body_def_id, assumed_wf_types);
+    let infcx_v2 = infcx.fork();
+    let implied_bounds = infcx_v2.implied_bounds_tys_v2(param_env, &assumed_wf_types);
     let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
+    let errors_v2 = infcx_v2.resolve_regions(&outlives_env);
+    if errors_v2.is_empty() {
+        return;
+    }
+
+    let implied_bounds = infcx.implied_bounds_tys(param_env, body_def_id, assumed_wf_types);
+    let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
+    let errors_v1 = infcx.resolve_regions(&outlives_env);
+    if !errors_v1.is_empty() {
+        infcx.err_ctxt().report_region_errors(body_def_id, &errors_v1);
+        return;
+    }
 
-    let _ = wfcx.ocx.resolve_regions_and_report_errors(body_def_id, &outlives_env);
+    let hir_id = tcx.hir().local_def_id_to_hir_id(body_def_id);
+    let (lint_level, _) = tcx
+        .lint_level_at_node(rustc_session::lint::builtin::IMPLIED_BOUNDS_FROM_TRAIT_IMPL, hir_id);
+    tcx.struct_span_lint_hir(
+        rustc_session::lint::builtin::IMPLIED_BOUNDS_FROM_TRAIT_IMPL,
+        hir_id,
+        tcx.def_span(body_def_id),
+        format!("{} is missing necessary lifetime bounds", tcx.def_descr(body_def_id.into())),
+        |lint| {
+            if !lint_level.is_error() {
+                lint.note(
+                    "to get more detailed errors, use `#[deny(implied_bounds_from_trait_impl)]`",
+                )
+            } else {
+                lint.note("more concrete lifetime errors are emitted below")
+            }
+        },
+    );
+    if lint_level.is_error() {
+        infcx_v2.err_ctxt().report_region_errors(body_def_id, &errors_v2);
+    }
 }
 
 fn check_well_formed(tcx: TyCtxt<'_>, def_id: hir::OwnerId) {

compiler/rustc_lint_defs/src/builtin.rs

@@ -3304,6 +3304,7 @@ declare_lint_pass! {
         ILL_FORMED_ATTRIBUTE_INPUT,
         ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
         IMPLIED_BOUNDS_ENTAILMENT,
+        IMPLIED_BOUNDS_FROM_TRAIT_IMPL,
         INCOMPLETE_INCLUDE,
         INDIRECT_STRUCTURAL_MATCH,
         INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
@@ -4172,3 +4173,44 @@ declare_lint! {
     Warn,
     "\"invalid_parameter\" isn't a valid argument for `#[macro_export]`",
 }
+
+declare_lint! {
+    /// The `implied_bounds_from_trait_impl` lint detects
+    /// a compiler bug allowed some code to assume invalid implied lifetime bounds.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![deny(implied_bounds_from_trait_impl)]
+    ///
+    /// trait Trait {
+    ///     type Assoc;
+    /// }
+    ///
+    /// impl<X: 'static> Trait for (X,) {
+    ///     type Assoc = ();
+    /// }
+    ///
+    /// struct Foo<T: Trait>(T)
+    /// where
+    ///     T::Assoc: Clone; // any bound using `T::Assoc`
+    ///
+    /// fn func(foo: Foo<(&str,)>) {
+    ///     let _: &'static str = foo.0.0;
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// FIXME: explanataion
+    ///
+    pub IMPLIED_BOUNDS_FROM_TRAIT_IMPL,
+    Warn,
+    "item uses illegal implied bounds derived from a trait impl",
+    @future_incompatible = FutureIncompatibleInfo {
+        reference: "issue #109628 <https://github.com/rust-lang/rust/issues/109628>",
+        reason: FutureIncompatibilityReason::FutureReleaseError,
+    };
+}

compiler/rustc_trait_selection/src/traits/outlives_bounds.rs

@@ -30,8 +30,7 @@ pub trait InferCtxtExt<'a, 'tcx> {
     fn implied_bounds_tys_v2(
         &'a self,
         param_env: ty::ParamEnv<'tcx>,
-        _body_id: LocalDefId,
-        tys: FxIndexSet<Ty<'tcx>>,
+        tys: &'a FxIndexSet<Ty<'tcx>>,
     ) -> BoundsV2<'a, 'tcx>;
 }
 
@@ -136,11 +135,10 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
     fn implied_bounds_tys_v2(
         &'a self,
         param_env: ParamEnv<'tcx>,
-        _body_id: LocalDefId,
-        tys: FxIndexSet<Ty<'tcx>>,
+        tys: &'a FxIndexSet<Ty<'tcx>>,
     ) -> BoundsV2<'a, 'tcx> {
-        tys.into_iter()
-            .flat_map(move |ty| {
+        tys.iter()
+            .flat_map(move |&ty| {
                 let ty = self.resolve_vars_if_possible(ty);
                 let ty = OpportunisticRegionResolver::new(self).fold_ty(ty);
                 if ty.has_infer() {

tests/ui/implied-bounds/from-trait-impl.rs

@@ -0,0 +1,39 @@
+trait Trait {
+    type Assoc;
+}
+
+impl<X: 'static> Trait for (X,) {
+    type Assoc = ();
+}
+
+struct Foo<T: Trait>(T)
+where
+    T::Assoc: Clone; // any predicate using `T::Assoc` works here
+
+fn func1(foo: Foo<(&str,)>) {
+//~^ WARN function is missing necessary lifetime bounds
+//~| WARN this was previously accepted
+    let _: &'static str = foo.0.0;
+}
+
+#[deny(implied_bounds_from_trait_impl)]
+fn func2(foo: Foo<(&str,)>) {
+//~^ ERROR function is missing necessary lifetime bounds
+//~| WARN this was previously accepted
+//~| ERROR `&str` does not fulfill the required lifetime
+    let _: &'static str = foo.0.0;
+}
+
+trait TestTrait {}
+
+impl<X> TestTrait for [Foo<(X,)>; 1] {}
+//~^ WARN implementation is missing necessary lifetime bounds
+//~| WARN this was previously accepted
+
+#[deny(implied_bounds_from_trait_impl)]
+impl<X> TestTrait for [Foo<(X,)>; 2] {}
+//~^ ERROR implementation is missing necessary lifetime bounds
+//~| WARN this was previously accepted
+//~| ERROR `X` may not live long enough
+
+fn main() {}

tests/ui/implied-bounds/from-trait-impl.stderr

@@ -0,0 +1,74 @@
+warning: function is missing necessary lifetime bounds
+  --> $DIR/from-trait-impl.rs:13:1
+   |
+LL | fn func1(foo: Foo<(&str,)>) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = 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 #109628 <https://github.com/rust-lang/rust/issues/109628>
+   = note: to get more detailed errors, use `#[deny(implied_bounds_from_trait_impl)]`
+   = note: `#[warn(implied_bounds_from_trait_impl)]` on by default
+
+error: function is missing necessary lifetime bounds
+  --> $DIR/from-trait-impl.rs:20:1
+   |
+LL | fn func2(foo: Foo<(&str,)>) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = 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 #109628 <https://github.com/rust-lang/rust/issues/109628>
+   = note: more concrete lifetime errors are emitted below
+note: the lint level is defined here
+  --> $DIR/from-trait-impl.rs:19:8
+   |
+LL | #[deny(implied_bounds_from_trait_impl)]
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0477]: the type `&str` does not fulfill the required lifetime
+  --> $DIR/from-trait-impl.rs:20:15
+   |
+LL | fn func2(foo: Foo<(&str,)>) {
+   |               ^^^^^^^^^^^^
+   |
+   = note: type must satisfy the static lifetime
+
+warning: implementation is missing necessary lifetime bounds
+  --> $DIR/from-trait-impl.rs:29:1
+   |
+LL | impl<X> TestTrait for [Foo<(X,)>; 1] {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = 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 #109628 <https://github.com/rust-lang/rust/issues/109628>
+   = note: to get more detailed errors, use `#[deny(implied_bounds_from_trait_impl)]`
+
+error: implementation is missing necessary lifetime bounds
+  --> $DIR/from-trait-impl.rs:34:1
+   |
+LL | impl<X> TestTrait for [Foo<(X,)>; 2] {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = 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 #109628 <https://github.com/rust-lang/rust/issues/109628>
+   = note: more concrete lifetime errors are emitted below
+note: the lint level is defined here
+  --> $DIR/from-trait-impl.rs:33:8
+   |
+LL | #[deny(implied_bounds_from_trait_impl)]
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0310]: the parameter type `X` may not live long enough
+  --> $DIR/from-trait-impl.rs:34:23
+   |
+LL | impl<X> TestTrait for [Foo<(X,)>; 2] {}
+   |                       ^^^^^^^^^^^^^^ ...so that the type `X` will meet its required lifetime bounds
+   |
+help: consider adding an explicit lifetime bound...
+   |
+LL | impl<X: 'static> TestTrait for [Foo<(X,)>; 2] {}
+   |       +++++++++
+
+error: aborting due to 4 previous errors; 2 warnings emitted
+
+Some errors have detailed explanations: E0310, E0477.
+For more information about an error, try `rustc --explain E0310`.