Rollup merge of #104295 - compiler-errors:rpitit-generics-parity, r=eholk

Check generics parity before collecting return-position `impl Trait`s in trait The only thing is that this duplicates the error message for number of generics mismatch, but we already deduplicate that error message in Cargo. I could add a flag to delay the error if the reviewer cares. Fixes #104281 Also drive-by adds a few comments to the `collect_trait_impl_trait_tys` method, and removes an unused argument from `compare_number_of_generics`.
2022-11-22 16:36:36 +05:30 · 2022-11-22 16:36:36 +05:30 · 680ba90f96
commit 680ba90f96
parent a78c9bee4d df5f247a5c
3 changed files with 65 additions and 32 deletions
--- a/compiler/rustc_hir_analysis/src/check/compare_method.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_method.rs
@ -14,10 +14,8 @@ use rustc_infer::traits::util;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::util::ExplicitSelf;
 use rustc_middle::ty::{
-    self, AssocItem, DefIdTree, TraitRef, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable,
-    TypeVisitable,
+    self, DefIdTree, InternalSubsts, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable,
 };
-use rustc_middle::ty::{FnSig, InternalSubsts};
 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
 use rustc_span::Span;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
@ -51,11 +49,11 @@ pub(crate) fn compare_impl_method<'tcx>(
        return;
    }

-    if let Err(_) = compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span) {
+    if let Err(_) = compare_number_of_generics(tcx, impl_m, trait_m, trait_item_span, false) {
        return;
    }

-    if let Err(_) = compare_generic_param_kinds(tcx, impl_m, trait_m) {
+    if let Err(_) = compare_generic_param_kinds(tcx, impl_m, trait_m, false) {
        return;
    }

@ -144,9 +142,9 @@ pub(crate) fn compare_impl_method<'tcx>(
 #[instrument(level = "debug", skip(tcx, impl_m_span, impl_trait_ref))]
 fn compare_predicate_entailment<'tcx>(
    tcx: TyCtxt<'tcx>,
-    impl_m: &AssocItem,
+    impl_m: &ty::AssocItem,
    impl_m_span: Span,
-    trait_m: &AssocItem,
+    trait_m: &ty::AssocItem,
    impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> Result<(), ErrorGuaranteed> {
    let trait_to_impl_substs = impl_trait_ref.substs;
@ -157,8 +155,7 @@ fn compare_predicate_entailment<'tcx>(
    // FIXME(@lcnr): remove that after removing `cause.body_id` from
    // obligations.
    let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
-    // We sometimes modify the span further down.
-    let mut cause = ObligationCause::new(
+    let cause = ObligationCause::new(
        impl_m_span,
        impl_m_hir_id,
        ObligationCauseCode::CompareImplItemObligation {
@ -307,14 +304,13 @@ fn compare_predicate_entailment<'tcx>(
        debug!(?terr, "sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);

        let emitted = report_trait_method_mismatch(
-            tcx,
-            &mut cause,
            &infcx,
+            cause,
            terr,
            (trait_m, trait_fty),
            (impl_m, impl_fty),
-            &trait_sig,
-            &impl_trait_ref,
+            trait_sig,
+            impl_trait_ref,
        );
        return Err(emitted);
    }
@ -352,11 +348,15 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
    let impl_trait_ref = tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap();
    let param_env = tcx.param_env(def_id);

+    // First, check a few of the same thing as `compare_impl_method`, just so we don't ICE during substitutions later.
+    compare_number_of_generics(tcx, impl_m, trait_m, tcx.hir().span_if_local(impl_m.def_id), true)?;
+    compare_generic_param_kinds(tcx, impl_m, trait_m, true)?;
+
    let trait_to_impl_substs = impl_trait_ref.substs;

    let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
    let return_span = tcx.hir().fn_decl_by_hir_id(impl_m_hir_id).unwrap().output.span();
-    let mut cause = ObligationCause::new(
+    let cause = ObligationCause::new(
        return_span,
        impl_m_hir_id,
        ObligationCauseCode::CompareImplItemObligation {
@ -376,6 +376,7 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
    let infcx = &tcx.infer_ctxt().build();
    let ocx = ObligationCtxt::new(infcx);

+    // Normalize the impl signature with fresh variables for lifetime inference.
    let norm_cause = ObligationCause::misc(return_span, impl_m_hir_id);
    let impl_sig = ocx.normalize(
        norm_cause.clone(),
@ -388,6 +389,10 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
    );
    let impl_return_ty = impl_sig.output();

+    // Normalize the trait signature with liberated bound vars, passing it through
+    // the ImplTraitInTraitCollector, which gathers all of the RPITITs and replaces
+    // them with inference variables.
+    // We will use these inference variables to collect the hidden types of RPITITs.
    let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_hir_id);
    let unnormalized_trait_sig = tcx
        .liberate_late_bound_regions(
@ -448,14 +453,13 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
            // emit an error now because `compare_predicate_entailment` will not report the error
            // when normalization fails.
            let emitted = report_trait_method_mismatch(
-                tcx,
-                &mut cause,
                infcx,
+                cause,
                terr,
                (trait_m, trait_fty),
                (impl_m, impl_fty),
-                &trait_sig,
-                &impl_trait_ref,
+                trait_sig,
+                impl_trait_ref,
            );
            return Err(emitted);
        }
@ -625,23 +629,21 @@ impl<'tcx> TypeFolder<'tcx> for ImplTraitInTraitCollector<'_, 'tcx> {
 }

 fn report_trait_method_mismatch<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    cause: &mut ObligationCause<'tcx>,
    infcx: &InferCtxt<'tcx>,
+    mut cause: ObligationCause<'tcx>,
    terr: TypeError<'tcx>,
-    (trait_m, trait_fty): (&AssocItem, Ty<'tcx>),
-    (impl_m, impl_fty): (&AssocItem, Ty<'tcx>),
-    trait_sig: &FnSig<'tcx>,
-    impl_trait_ref: &TraitRef<'tcx>,
+    (trait_m, trait_fty): (&ty::AssocItem, Ty<'tcx>),
+    (impl_m, impl_fty): (&ty::AssocItem, Ty<'tcx>),
+    trait_sig: ty::FnSig<'tcx>,
+    impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> ErrorGuaranteed {
+    let tcx = infcx.tcx;
    let (impl_err_span, trait_err_span) =
        extract_spans_for_error_reporting(&infcx, terr, &cause, impl_m, trait_m);

-    cause.span = impl_err_span;
-
    let mut diag = struct_span_err!(
        tcx.sess,
-        cause.span(),
+        impl_err_span,
        E0053,
        "method `{}` has an incompatible type for trait",
        trait_m.name
@ -712,6 +714,7 @@ fn report_trait_method_mismatch<'tcx>(
        _ => {}
    }

+    cause.span = impl_err_span;
    infcx.err_ctxt().note_type_err(
        &mut diag,
        &cause,
@ -922,9 +925,9 @@ fn compare_self_type<'tcx>(
 fn compare_number_of_generics<'tcx>(
    tcx: TyCtxt<'tcx>,
    impl_: &ty::AssocItem,
-    _impl_span: Span,
    trait_: &ty::AssocItem,
    trait_span: Option<Span>,
+    delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
    let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
    let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
@ -1054,7 +1057,7 @@ fn compare_number_of_generics<'tcx>(
                err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
            }

-            let reported = err.emit();
+            let reported = err.emit_unless(delay);
            err_occurred = Some(reported);
        }
    }
@ -1306,6 +1309,7 @@ fn compare_generic_param_kinds<'tcx>(
    tcx: TyCtxt<'tcx>,
    impl_item: &ty::AssocItem,
    trait_item: &ty::AssocItem,
+    delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
    assert_eq!(impl_item.kind, trait_item.kind);

@ -1363,7 +1367,7 @@ fn compare_generic_param_kinds<'tcx>(
            err.span_label(impl_header_span, "");
            err.span_label(param_impl_span, make_param_message("found", param_impl));

-            let reported = err.emit();
+            let reported = err.emit_unless(delay);
            return Err(reported);
        }
    }
@ -1489,9 +1493,9 @@ pub(crate) fn compare_ty_impl<'tcx>(
    debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);

    let _: Result<(), ErrorGuaranteed> = (|| {
-        compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
+        compare_number_of_generics(tcx, impl_ty, trait_ty, trait_item_span, false)?;

-        compare_generic_param_kinds(tcx, impl_ty, trait_ty)?;
+        compare_generic_param_kinds(tcx, impl_ty, trait_ty, false)?;

        let sp = tcx.def_span(impl_ty.def_id);
        compare_type_predicate_entailment(tcx, impl_ty, sp, trait_ty, impl_trait_ref)?;
--- a/src/test/ui/impl-trait/in-trait/trait-more-generics-than-impl.rs
+++ b/src/test/ui/impl-trait/in-trait/trait-more-generics-than-impl.rs
@ -0,0 +1,17 @@
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+struct S;
+
+trait Foo {
+    fn bar<T>() -> impl Sized;
+}
+
+impl Foo for S {
+    fn bar() -> impl Sized {}
+    //~^ ERROR method `bar` has 0 type parameters but its trait declaration has 1 type parameter
+}
+
+fn main() {
+    S::bar();
+}
--- a/src/test/ui/impl-trait/in-trait/trait-more-generics-than-impl.stderr
+++ b/src/test/ui/impl-trait/in-trait/trait-more-generics-than-impl.stderr
@ -0,0 +1,12 @@
+error[E0049]: method `bar` has 0 type parameters but its trait declaration has 1 type parameter
+  --> $DIR/trait-more-generics-than-impl.rs:11:11
+   |
+LL |     fn bar<T>() -> impl Sized;
+   |            - expected 1 type parameter
+...
+LL |     fn bar() -> impl Sized {}
+   |           ^ found 0 type parameters
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0049`.