Fix tuples being invariant

super-tuple · daboross · jackh726 · commit 7fc9755ff013 · 2020-11-10T16:41:16.000-05:00
Tuples should always be covariant over their inner types.

Co-authored-by: David Ross &lt;daboross@daboross.net&gt;
diff --git a/chalk-solve/src/infer/unify.rs b/chalk-solve/src/infer/unify.rs
@@ -218,7 +218,10 @@ impl<'t, I: Interner> Unifier<'t, I> {
                 }
                 self.zip_substs(
                     variance,
-                    None,
+                    Some(Variances::from(
+                        &self.interner,
+                        std::iter::repeat(Variance::Covariant).take(*arity_a),
+                    )),
                     substitution_a.as_slice(interner),
                     substitution_b.as_slice(interner),
                 )

Original file line number	Diff line number	Diff line change
`@@ -218,7 +218,10 @@ impl<'t, I: Interner> Unifier<'t, I> {`
`218`	`218`	`}`
`219`	`219`	`self.zip_substs(`
`220`	`220`	`variance,`
`221`		`- None,`
	`221`	`+ Some(Variances::from(`
	`222`	`+ &self.interner,`
	`223`	`+ std::iter::repeat(Variance::Covariant).take(*arity_a),`
	`224`	`+ )),`
`222`	`225`	`substitution_a.as_slice(interner),`
`223`	`226`	`substitution_b.as_slice(interner),`
`224`	`227`	`)`