trait_sel: const {Meta,}Sized in impl headers

Now that sizedness traits have been made const, pretty printing of impl
headers should print the constness of the sizedness trait.

Author: davidtwco

compiler/rustc_middle/src/ty/predicate.rs

@@ -208,6 +208,15 @@ impl<'tcx> Clause<'tcx> {
         }
     }
 
+    pub fn as_host_effect_clause(self) -> Option<ty::Binder<'tcx, HostEffectPredicate<'tcx>>> {
+        let clause = self.kind();
+        if let ty::ClauseKind::HostEffect(host_effect_clause) = clause.skip_binder() {
+            Some(clause.rebind(host_effect_clause))
+        } else {
+            None
+        }
+    }
+
     pub fn as_projection_clause(self) -> Option<ty::Binder<'tcx, ProjectionPredicate<'tcx>>> {
         let clause = self.kind();
         if let ty::ClauseKind::Projection(projection_clause) = clause.skip_binder() {

compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs

@@ -340,7 +340,9 @@ pub(crate) fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Opti
 
     #[derive(Debug, Default)]
     struct SizednessFound {
+        const_sized: bool,
         sized: bool,
+        const_metasized: bool,
         metasized: bool,
     }
 
@@ -389,21 +391,36 @@ pub(crate) fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Opti
             }
         }
 
+        if let Some(host_effect_clause) = p.as_host_effect_clause() {
+            let self_ty = host_effect_clause.self_ty().skip_binder();
+            let sizedness_of = types_with_sizedness_bounds.entry(self_ty).or_default();
+            if Some(host_effect_clause.def_id()) == sized_trait {
+                sizedness_of.const_sized = true;
+                continue;
+            } else if Some(host_effect_clause.def_id()) == metasized_trait {
+                sizedness_of.const_metasized = true;
+                continue;
+            }
+        }
+
         pretty_predicates.push(p.to_string());
     }
 
     for (ty, sizedness) in types_with_sizedness_bounds {
         debug!(?ty, ?sizedness);
         if !tcx.features().sized_hierarchy() {
-            if sizedness.sized {
+            if sizedness.const_sized || sizedness.sized {
                 // Maybe a default bound, don't write anything.
             } else {
                 pretty_predicates.push(format!("{ty}: ?Sized"));
             }
         } else {
-            if sizedness.sized {
+            if sizedness.const_sized {
                 // Maybe a default bound, don't write anything.
+            } else if sizedness.sized {
                 pretty_predicates.push(format!("{ty}: Sized"));
+            } else if sizedness.const_metasized {
+                pretty_predicates.push(format!("{ty}: const MetaSized"));
             } else if sizedness.metasized {
                 pretty_predicates.push(format!("{ty}: MetaSized"));
             } else {

tests/ui/sized-hierarchy/auxiliary/pretty-print-dep.rs

@@ -1,7 +1,11 @@
-#![feature(sized_hierarchy)]
+#![feature(const_trait_impl, sized_hierarchy)]
 
 use std::marker::{MetaSized, PointeeSized};
 
+pub trait ConstSizedTr {}
+
+impl<T: const Sized> ConstSizedTr for T {}
+
 pub trait SizedTr {}
 
 impl<T: Sized> SizedTr for T {}
@@ -10,6 +14,10 @@ pub trait NegSizedTr {}
 
 impl<T: ?Sized> NegSizedTr for T {}
 
+pub trait ConstMetaSizedTr {}
+
+impl<T: const MetaSized> ConstMetaSizedTr for T {}
+
 pub trait MetaSizedTr {}
 
 impl<T: MetaSized> MetaSizedTr for T {}

tests/ui/sized-hierarchy/pretty-print.rs

@@ -1,6 +1,6 @@
 //@ aux-build:pretty-print-dep.rs
 //@ compile-flags: --crate-type=lib
-#![feature(sized_hierarchy)]
+#![feature(const_trait_impl, sized_hierarchy)]
 
 // Test that printing the sizedness trait bounds in the conflicting impl error with
 // `sized_hierarchy` enabled prints all of the appropriate bounds.
@@ -11,16 +11,22 @@
 use std::marker::{MetaSized, PointeeSized};
 
 extern crate pretty_print_dep;
-use pretty_print_dep::{SizedTr, MetaSizedTr, PointeeSizedTr};
+use pretty_print_dep::{ConstSizedTr, SizedTr, ConstMetaSizedTr, MetaSizedTr, PointeeSizedTr};
 
 struct X<T>(T);
 
+impl<T: const Sized> ConstSizedTr for X<T> {}
+//~^ ERROR conflicting implementations of trait `ConstSizedTr` for type `X<_>`
+
 impl<T: Sized> SizedTr for X<T> {}
 //~^ ERROR conflicting implementations of trait `SizedTr` for type `X<_>`
 
 impl<T: ?Sized> pretty_print_dep::NegSizedTr for X<T> {}
 //~^ ERROR conflicting implementations of trait `NegSizedTr` for type `X<_>`
 
+impl<T: const MetaSized> ConstMetaSizedTr for X<T> {}
+//~^ ERROR conflicting implementations of trait `ConstMetaSizedTr` for type `X<_>`
+
 impl<T: MetaSized> MetaSizedTr for X<T> {}
 //~^ ERROR conflicting implementations of trait `MetaSizedTr` for type `X<_>`
 

tests/ui/sized-hierarchy/pretty-print.stderr

@@ -1,6 +1,15 @@
-error[E0119]: conflicting implementations of trait `SizedTr` for type `X<_>`
+error[E0119]: conflicting implementations of trait `ConstSizedTr` for type `X<_>`
   --> $DIR/pretty-print.rs:18:1
    |
+LL | impl<T: const Sized> ConstSizedTr for X<T> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `pretty_print_dep`:
+           - impl<T> ConstSizedTr for T;
+
+error[E0119]: conflicting implementations of trait `SizedTr` for type `X<_>`
+  --> $DIR/pretty-print.rs:21:1
+   |
 LL | impl<T: Sized> SizedTr for X<T> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
@@ -9,17 +18,27 @@ LL | impl<T: Sized> SizedTr for X<T> {}
              where T: Sized;
 
 error[E0119]: conflicting implementations of trait `NegSizedTr` for type `X<_>`
-  --> $DIR/pretty-print.rs:21:1
+  --> $DIR/pretty-print.rs:24:1
    |
 LL | impl<T: ?Sized> pretty_print_dep::NegSizedTr for X<T> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: conflicting implementation in crate `pretty_print_dep`:
            - impl<T> NegSizedTr for T
-             where T: MetaSized;
+             where T: const MetaSized;
+
+error[E0119]: conflicting implementations of trait `ConstMetaSizedTr` for type `X<_>`
+  --> $DIR/pretty-print.rs:27:1
+   |
+LL | impl<T: const MetaSized> ConstMetaSizedTr for X<T> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `pretty_print_dep`:
+           - impl<T> ConstMetaSizedTr for T
+             where T: const MetaSized;
 
 error[E0119]: conflicting implementations of trait `MetaSizedTr` for type `X<_>`
-  --> $DIR/pretty-print.rs:24:1
+  --> $DIR/pretty-print.rs:30:1
    |
 LL | impl<T: MetaSized> MetaSizedTr for X<T> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -29,7 +48,7 @@ LL | impl<T: MetaSized> MetaSizedTr for X<T> {}
              where T: MetaSized;
 
 error[E0119]: conflicting implementations of trait `PointeeSizedTr` for type `X<_>`
-  --> $DIR/pretty-print.rs:27:1
+  --> $DIR/pretty-print.rs:33:1
    |
 LL | impl<T: PointeeSized> PointeeSizedTr for X<T> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -38,6 +57,6 @@ LL | impl<T: PointeeSized> PointeeSizedTr for X<T> {}
            - impl<T> PointeeSizedTr for T
              where T: PointeeSized;
 
-error: aborting due to 4 previous errors
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0119`.