Get rid of `StructurallyRelateAliases` by adwinwhite · Pull Request #158731 · rust-lang/rust

adwinwhite · 2026-07-03T12:58:42Z

Part of #155345

Finally we can get rid of the last use of StructurallyRelateAliases::Yes.

r? lcnr

rustbot · 2026-07-03T12:58:45Z

changes to the core type system

cc @lcnr

rust-log-analyzer · 2026-07-03T13:35:51Z

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [ui] tests/ui/mismatched_types/closure-mismatch.rs#next stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/mismatched_types/closure-mismatch.next/closure-mismatch.next.stderr`
diff of stderr:

- error[E0277]: the trait bound `{closure@$DIR/closure-mismatch.rs:12:9: 12:12}: Foo` is not satisfied
+ error[E0277]: the trait bound `for<'a> {closure@$DIR/closure-mismatch.rs:12:9: 12:12}: Foo` is not satisfied
2   --> $DIR/closure-mismatch.rs:12:9
3    |
4 LL |     baz(|_| ());

-    |     --- ^^^^^^ unsatisfied trait bound
+    |     --- ^^^^^^ the trait `for<'a> Foo` is not implemented for `for<'a> {closure@$DIR/closure-mismatch.rs:12:9: 12:12}`
6    |     |
7    |     required by a bound introduced by this call
8    |

-    = help: the trait `for<'a> FnOnce(&'a ())` is not implemented for closure `{closure@$DIR/closure-mismatch.rs:12:9: 12:12}`
-    = note: expected a closure with signature `for<'a> fn(&'a ())`
-               found a closure with signature `fn(&())`
- note: this is a known limitation of the trait solver that will be lifted in the future
-   --> $DIR/closure-mismatch.rs:12:9
-    |
- LL |     baz(|_| ());
-    |     ----^^^----
-    |     |   |
-    |     |   the trait solver is unable to infer the generic types that should be inferred from this argument
-    |     add turbofish arguments to this call to specify the types manually, even if it's redundant
- note: required for `{closure@$DIR/closure-mismatch.rs:12:9: 12:12}` to implement `Foo`
+ note: required for `{closure@$DIR/closure-mismatch.rs:12:9: 12:12}` to implement `for<'a> Foo`
21   --> $DIR/closure-mismatch.rs:7:18
22    |
23 LL | impl<T: Fn(&())> Foo for T {}

29    |
30 LL | fn baz<T: Foo>(_: T) {}
31    |           ^^^ required by this bound in `baz`
+ help: consider borrowing here
+    |
+ LL |     baz(&|_| ());
+    |         +
32 
- error[E0277]: the trait bound `{closure@$DIR/closure-mismatch.rs:16:9: 16:12}: Foo` is not satisfied
+ error[E0277]: the trait bound `for<'a> {closure@$DIR/closure-mismatch.rs:16:9: 16:12}: Foo` is not satisfied
34   --> $DIR/closure-mismatch.rs:16:9
35    |
36 LL |     baz(|x| ());

-    |     --- ^^^^^^ unsatisfied trait bound
+    |     --- ^^^^^^ the trait `for<'a> Foo` is not implemented for `for<'a> {closure@$DIR/closure-mismatch.rs:16:9: 16:12}`
38    |     |
39    |     required by a bound introduced by this call
40    |

-    = help: the trait `for<'a> FnOnce(&'a ())` is not implemented for closure `{closure@$DIR/closure-mismatch.rs:16:9: 16:12}`
-    = note: expected a closure with signature `for<'a> fn(&'a ())`
-               found a closure with signature `fn(&())`
- note: this is a known limitation of the trait solver that will be lifted in the future
-   --> $DIR/closure-mismatch.rs:16:9
-    |
- LL |     baz(|x| ());
-    |     ----^^^----
-    |     |   |
-    |     |   the trait solver is unable to infer the generic types that should be inferred from this argument
-    |     add turbofish arguments to this call to specify the types manually, even if it's redundant
- note: required for `{closure@$DIR/closure-mismatch.rs:16:9: 16:12}` to implement `Foo`
+ note: required for `{closure@$DIR/closure-mismatch.rs:16:9: 16:12}` to implement `for<'a> Foo`
53   --> $DIR/closure-mismatch.rs:7:18
54    |
55 LL | impl<T: Fn(&())> Foo for T {}

61    |
62 LL | fn baz<T: Foo>(_: T) {}
63    |           ^^^ required by this bound in `baz`
+ help: consider borrowing here
+    |
+ LL |     baz(&|x| ());
+    |         +
64 
65 error: aborting due to 2 previous errors
66 

Note: some mismatched output was normalized before being compared
- error[E0277]: the trait bound `for<'a> {closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:12:9: 12:12}: Foo` is not satisfied
-   --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:12:9
-    |     --- ^^^^^^ the trait `for<'a> Foo` is not implemented for `for<'a> {closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:12:9: 12:12}`
- note: required for `{closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:12:9: 12:12}` to implement `for<'a> Foo`
-   --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:7:18
- error[E0277]: the trait bound `for<'a> {closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:16:9: 16:12}: Foo` is not satisfied
-   --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:16:9
-    |     --- ^^^^^^ the trait `for<'a> Foo` is not implemented for `for<'a> {closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:16:9: 16:12}`
- note: required for `{closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:16:9: 16:12}` to implement `for<'a> Foo`
-   --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:7:18
+ error[E0277]: the trait bound `for<'a> {closure@$DIR/closure-mismatch.rs:12:9: 12:12}: Foo` is not satisfied
+    |     --- ^^^^^^ the trait `for<'a> Foo` is not implemented for `for<'a> {closure@$DIR/closure-mismatch.rs:12:9: 12:12}`
+ note: required for `{closure@$DIR/closure-mismatch.rs:12:9: 12:12}` to implement `for<'a> Foo`
+ help: consider borrowing here
+    |
+ LL |     baz(&|_| ());
+    |         +
+ error[E0277]: the trait bound `for<'a> {closure@$DIR/closure-mismatch.rs:16:9: 16:12}: Foo` is not satisfied
+    |     --- ^^^^^^ the trait `for<'a> Foo` is not implemented for `for<'a> {closure@$DIR/closure-mismatch.rs:16:9: 16:12}`
+ note: required for `{closure@$DIR/closure-mismatch.rs:16:9: 16:12}` to implement `for<'a> Foo`
+ help: consider borrowing here
+    |
+ LL |     baz(&|x| ());
+    |         +


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args mismatched_types/closure-mismatch.rs`

error in revision `next`: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/mismatched_types/closure-mismatch.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--cfg" "next" "--check-cfg" "cfg(test,FALSE,current,next)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/mismatched_types/closure-mismatch.next" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Znext-solver"
stdout: none
--- stderr -------------------------------
error[E0277]: the trait bound `for<'a> {closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:12:9: 12:12}: Foo` is not satisfied
##[error]  --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:12:9
   |
LL |     baz(|_| ());
   |     --- ^^^^^^ the trait `for<'a> Foo` is not implemented for `for<'a> {closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:12:9: 12:12}`
   |     |
   |     required by a bound introduced by this call
   |
note: required for `{closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:12:9: 12:12}` to implement `for<'a> Foo`
  --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:7:18
   |
LL | impl<T: Fn(&())> Foo for T {}
   |         -------  ^^^     ^
   |         |
   |         unsatisfied trait bound introduced here
note: required by a bound in `baz`
  --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:9:11
   |
LL | fn baz<T: Foo>(_: T) {}
   |           ^^^ required by this bound in `baz`
help: consider borrowing here
   |
LL |     baz(&|_| ());
   |         +

error[E0277]: the trait bound `for<'a> {closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:16:9: 16:12}: Foo` is not satisfied
##[error]  --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:16:9
   |
LL |     baz(|x| ());
   |     --- ^^^^^^ the trait `for<'a> Foo` is not implemented for `for<'a> {closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:16:9: 16:12}`
   |     |
   |     required by a bound introduced by this call
   |
note: required for `{closure@/checkout/tests/ui/mismatched_types/closure-mismatch.rs:16:9: 16:12}` to implement `for<'a> Foo`
  --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:7:18
   |
LL | impl<T: Fn(&())> Foo for T {}
   |         -------  ^^^     ^
   |         |
   |         unsatisfied trait bound introduced here
note: required by a bound in `baz`
  --> /checkout/tests/ui/mismatched_types/closure-mismatch.rs:9:11
   |
LL | fn baz<T: Foo>(_: T) {}
   |           ^^^ required by this bound in `baz`
help: consider borrowing here
   |
LL |     baz(&|x| ());
   |         +

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0277`.

lcnr · 2026-07-03T13:52:59Z

        self.inner.borrow_mut().const_unification_table().union(a, b);
    }

+    fn equate_ty_var_raw(&self, vid: ty::TyVid, ty: Ty<'tcx>) {


please name them instantiate instead of equate

View changes since the review

lcnr · 2026-07-03T13:53:44Z

    })
 }

+/// Enforce that `a` is equal to `b`.


should comment

how is it different from eq

why does it exist

where is it used

View changes since the review

lcnr · 2026-07-03T13:54:57Z

+            }
+
+            (ty::Infer(ty::TyVar(a_vid)), _) => {
+                infcx.equate_ty_var_raw(a_vid, b);


can you add a debug_assert to instantiate_ty_var_raw tht the type we instantiate it with does not refer to anything from a higher universe?

View changes since the review

same for regions and consts :>

lcnr · 2026-07-03T13:56:16Z

+        let a = infcx.shallow_resolve_const(a);
+        let b = infcx.shallow_resolve_const(b);


we should be able to not do that but debug_assert that this is a noop?

View changes since the review

lcnr · 2026-07-03T13:58:03Z

+        if let Some(a_inner) = a.no_bound_vars()
+            && let Some(b_inner) = b.no_bound_vars()


a and b have exactly the same bound vars here. we don't have to bother with the rebinding 🤔 actually, we can just recurse without instantiating bound vars at all

we can just assert that the bound vars are equal, and then recurse :>

View changes since the review

lcnr

beautiful ❤️ i love rigid aliases

View changes since this review

rust-bors · 2026-07-05T10:55:18Z

☔ The latest upstream changes (presumably #158795) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

adwinwhite added 3 commits July 3, 2026 20:40

refactor normalization in coerce_shared_info

556d2ce

new relating for response

069e30a

remove StructurallyRelateAliases

4a27c1d

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Jul 3, 2026

rustbot assigned lcnr Jul 3, 2026

lcnr reviewed Jul 3, 2026

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Get rid of `StructurallyRelateAliases`#158731

Get rid of `StructurallyRelateAliases`#158731
adwinwhite wants to merge 3 commits into
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adwinwhite:rid-structurally-relate-aliases

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		let a = infcx.shallow_resolve_const(a);
		let b = infcx.shallow_resolve_const(b);

		if let Some(a_inner) = a.no_bound_vars()
		&& let Some(b_inner) = b.no_bound_vars()

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