Auto merge of #759 - flodiebold:function-pointer-unification, r=nikomatsakis

Fix function pointers of different param counts unifying

Author: bors

chalk-ir/src/zip.rs

@@ -525,12 +525,12 @@ impl<I: Interner> Zip<I> for FnSubst<I> {
     ) -> Fallible<()> {
         let interner = zipper.interner();
         // Parameters
-        for (a, b) in a.0.as_slice(interner)[..a.0.len(interner) - 1]
-            .iter()
-            .zip(b.0.as_slice(interner)[..b.0.len(interner) - 1].iter())
-        {
-            Zip::zip_with(zipper, variance.xform(Variance::Contravariant), a, b)?;
-        }
+        Zip::zip_with(
+            zipper,
+            variance.xform(Variance::Contravariant),
+            &a.0.as_slice(interner)[..a.0.len(interner) - 1],
+            &b.0.as_slice(interner)[..b.0.len(interner) - 1],
+        )?;
         // Return type
         Zip::zip_with(
             zipper,

tests/test/unify.rs

@@ -149,6 +149,13 @@ fn forall_equality() {
             expect![["Unique"]]
         }
 
+        goal {
+            // Function pointers with different parameters should not be equal.
+            fn(u32): Eq<fn(u32, u32)>
+        } yields {
+            expect![["No possible solution"]]
+        }
+
         goal {
             // Variadic function pointers should not be equal to non-variadic fn pointers.
             fn(u8, ...): Eq<fn(u8)>