Merge pull request #21241 from ShoyuVanilla/issue-20487-again

fix: Support dyn compatibility for old toolchains without `MetaSized`

Author: ChayimFriedman2

crates/hir-ty/src/dyn_compatibility.rs

@@ -427,9 +427,14 @@ fn receiver_is_dispatchable<'db>(
     };
 
     let meta_sized_did = lang_items.MetaSized;
-    let Some(meta_sized_did) = meta_sized_did else {
-        return false;
-    };
+
+    // TODO: This is for supporting dyn compatibility for toolchains doesn't contain `MetaSized`
+    // trait. Uncomment and short circuit here once `MINIMUM_SUPPORTED_TOOLCHAIN_VERSION`
+    // become > 1.88.0
+    //
+    // let Some(meta_sized_did) = meta_sized_did else {
+    //     return false;
+    // };
 
     // Type `U`
     // FIXME: That seems problematic to fake a generic param like that?
@@ -450,17 +455,16 @@ fn receiver_is_dispatchable<'db>(
         });
         let trait_predicate = TraitRef::new_from_args(interner, trait_.into(), args);
 
-        let meta_sized_predicate =
-            TraitRef::new(interner, meta_sized_did.into(), [unsized_self_ty]);
+        let meta_sized_predicate = meta_sized_did
+            .map(|did| TraitRef::new(interner, did.into(), [unsized_self_ty]).upcast(interner));
 
         ParamEnv {
             clauses: Clauses::new_from_iter(
                 interner,
-                generic_predicates.iter_identity_copied().chain([
-                    unsize_predicate.upcast(interner),
-                    trait_predicate.upcast(interner),
-                    meta_sized_predicate.upcast(interner),
-                ]),
+                generic_predicates
+                    .iter_identity_copied()
+                    .chain([unsize_predicate.upcast(interner), trait_predicate.upcast(interner)])
+                    .chain(meta_sized_predicate),
             ),
         }
     };

crates/hir-ty/src/tests/regression/new_solver.rs

@@ -226,6 +226,62 @@ fn debug(_: &dyn Foo) {}
 
 impl Foo for i32 {}
 
+fn main() {
+    debug(&1);
+}"#,
+    );
+
+    // toolchains <= 1.88.0, before sized-hierarchy.
+    check_no_mismatches(
+        r#"
+#[lang = "sized"]
+pub trait Sized {}
+
+#[lang = "unsize"]
+pub trait Unsize<T: ?Sized> {}
+
+#[lang = "coerce_unsized"]
+pub trait CoerceUnsized<T: ?Sized> {}
+
+impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a mut U> for &'a mut T {}
+
+impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b mut T {}
+
+impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for &'a mut T {}
+
+impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for &'a mut T {}
+
+impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
+
+impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for &'a T {}
+
+impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
+
+impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *mut T {}
+
+impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *const T {}
+
+#[lang = "dispatch_from_dyn"]
+pub trait DispatchFromDyn<T> {}
+
+impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<&'a U> for &'a T {}
+
+impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<&'a mut U> for &'a mut T {}
+
+impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<*const U> for *const T {}
+
+impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<*mut U> for *mut T {}
+
+trait Foo {
+    fn bar(&self) -> u32 {
+        0xCAFE
+    }
+}
+
+fn debug(_: &dyn Foo) {}
+
+impl Foo for i32 {}
+
 fn main() {
     debug(&1);
 }"#,

crates/rust-analyzer/src/lib.rs

@@ -14,7 +14,7 @@ extern crate ra_ap_rustc_type_ir as rustc_type_ir;
 /// Any toolchain less than this version will likely not work with rust-analyzer built from this revision.
 pub const MINIMUM_SUPPORTED_TOOLCHAIN_VERSION: semver::Version = semver::Version {
     major: 1,
-    minor: 90,
+    minor: 78,
     patch: 0,
     pre: semver::Prerelease::EMPTY,
     build: semver::BuildMetadata::EMPTY,