fix problem with specializing rigids

compiler/gen/tests/gen_primitives.rs

@@ -530,6 +530,24 @@ mod gen_primitives {
 
     #[test]
     #[ignore]
+    fn top_level_constant() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                app LinkedListLen0 provides [ main ] imports []
+
+                pi = 3.1415
+
+                main =
+                    pi + pi
+                    "#
+            ),
+            3.1415 + 3.1415,
+            f64
+        );
+    }
+
+    #[test]
     fn linked_list_len_0() {
         assert_evals_to!(
             indoc!(
@@ -538,8 +556,8 @@ mod gen_primitives {
 
                 LinkedList a : [ Nil, Cons a (LinkedList a) ]
 
-                nil : LinkedList Int
-                nil = Nil
+                nil : {} -> LinkedList Int
+                nil = \_ -> Nil
 
                 length : LinkedList a -> Int
                 length = \list ->
@@ -549,7 +567,7 @@ mod gen_primitives {
 
 
                 main =
-                    length nil
+                    length (nil {})
                     "#
             ),
             0,

compiler/gen/tests/helpers/eval.rs

@@ -282,7 +282,7 @@ macro_rules! assert_evals_to {
         // parsing the source, so that there's no chance their passing
         // or failing depends on leftover state from the previous one.
         {
-            //assert_llvm_evals_to!($src, $expected, $ty, $transform, $leak);
+            assert_llvm_evals_to!($src, $expected, $ty, $transform, $leak);
         }
         {
             assert_opt_evals_to!($src, $expected, $ty, $transform, $leak);

compiler/mono/src/ir.rs

@@ -1365,10 +1365,12 @@ fn specialize_external<'a>(
 
     // unify the called function with the specialized signature, then specialize the function body
     let snapshot = env.subs.snapshot();
+    let cache_snapshot = layout_cache.snapshot();
 
     let unified = roc_unify::unify::unify(env.subs, annotation, fn_var);
 
-    debug_assert!(matches!(unified, roc_unify::unify::Unified::Success(_)));
+    let is_valid = matches!(unified, roc_unify::unify::Unified::Success(_));
+    debug_assert!(is_valid);
 
     let specialized_body = from_can(env, body, procs, layout_cache);
 
@@ -1376,6 +1378,7 @@ fn specialize_external<'a>(
         build_specialized_proc_from_var(env, layout_cache, pattern_symbols, fn_var)?;
 
     // reset subs, so we don't get type errors when specializing for a different signature
+    layout_cache.rollback_to(cache_snapshot);
     env.subs.rollback_to(snapshot);
 
     // TODO WRONG

compiler/solve/src/solve.rs

@@ -1227,8 +1227,6 @@ fn instantiate_rigids_help(
 
     if let Some(copy) = desc.copy.into_variable() {
         return copy;
-    } else if desc.rank != Rank::NONE {
-        return var;
     }
 
     let make_descriptor = |content| Descriptor {

compiler/unify/src/unify.rs

@@ -681,7 +681,7 @@ fn unify_shared_tags(
 
         merge(subs, ctx, Structure(flat_type))
     } else {
-        mismatch!()
+        mismatch!("Problem with Tag Union")
     }
 }
 
@@ -911,7 +911,7 @@ fn unify_rigid(subs: &mut Subs, ctx: &Context, name: &Lowercase, other: &Content
         RigidVar(_) | Structure(_) | Alias(_, _, _) => {
             // Type mismatch! Rigid can only unify with flex, even if the
             // rigid names are the same.
-            mismatch!()
+            mismatch!("Rigid with {:?}", &other)
         }
         Error => {
             // Error propagates.