Rollup merge of rust-lang#98499 - JulianKnodt:erase_lifetime, r=lcnr

Erase regions in New Abstract Consts

When an abstract const is constructed, we previously included lifetimes in the set of substitutes, so it was not able to unify two abstract consts if their lifetimes did not match but the values did, despite the values not depending on the lifetimes. This caused code that should have compiled to not compile.

Fixes rust-lang#98452

r? ``@lcnr``

Author: Dylan-DPC

compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -236,7 +236,7 @@ impl<'tcx> AbstractConst<'tcx> {
     ) -> Result<Option<AbstractConst<'tcx>>, ErrorGuaranteed> {
         let inner = tcx.thir_abstract_const_opt_const_arg(uv.def)?;
         debug!("AbstractConst::new({:?}) = {:?}", uv, inner);
-        Ok(inner.map(|inner| AbstractConst { inner, substs: uv.substs }))
+        Ok(inner.map(|inner| AbstractConst { inner, substs: tcx.erase_regions(uv.substs) }))
     }
 
     pub fn from_const(
@@ -416,6 +416,7 @@ impl<'a, 'tcx> AbstractConstBuilder<'a, 'tcx> {
                     // `AbstractConst`s should not contain any promoteds as they require references which
                     // are not allowed.
                     assert_eq!(ct.promoted, None);
+                    assert_eq!(ct, self.tcx.erase_regions(ct));
                 }
             }
         }

src/test/ui/const-generics/try_unify_ignore_lifetimes.rs

@@ -0,0 +1,33 @@
+// check-pass
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+struct Num<const N: usize>;
+
+trait NumT {
+    const VALUE: usize;
+}
+
+impl<const N: usize> NumT for Num<N> {
+    const VALUE: usize = N;
+}
+
+struct Foo<'a, N: NumT>(&'a [u32; N::VALUE]) where [(); N::VALUE]:;
+
+trait Bar {
+    type Size: NumT;
+
+    fn bar<'a>(foo: &Foo<'a, Self::Size>) where [(); Self::Size::VALUE]: {
+        todo!();
+    }
+}
+
+trait Baz<'a> {
+    type Size: NumT;
+
+    fn baz(foo: &Foo<'a, Self::Size>) where [(); Self::Size::VALUE]: {
+        todo!();
+    }
+}
+
+fn main() {}