Check in gen test for record decoding!

crates/compiler/solve/src/ability.rs

@@ -584,7 +584,15 @@ trait DerivableVisitor {
                         let descend = Self::visit_record(var)?;
                         if descend.0 {
                             push_var_slice!(fields.variables());
-                            stack.push(ext);
+                            if !matches!(
+                                subs.get_content_without_compacting(ext),
+                                Content::FlexVar(_) | Content::RigidVar(_)
+                            ) {
+                                // TODO: currently, just we suppose the presence of a flex var may
+                                // include more or less things which we can derive. But, we should
+                                // instead recurse here, and add a `t ~ u | u has Decode` constraint as needed.
+                                stack.push(ext);
+                            }
                         }
                     }
                     TagUnion(tags, ext) => {

crates/compiler/test_gen/src/gen_abilities.rs

@@ -954,11 +954,7 @@ fn encode_then_decode_list_of_lists_of_strings() {
 }
 
 #[test]
-#[cfg(all(
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
-    any(feature = "gen-llvm"), // currently fails on gen-wasm
-    not(feature = "gen-llvm-wasm") // hits a stack limit in wasm3
-))]
-#[ignore]
 fn decode_record_two_fields() {
     assert_evals_to!(
         indoc!(
@@ -967,11 +963,11 @@ fn decode_record_two_fields() {
 
             main =
                 when Str.toUtf8 "{\"first\":\"ab\",\"second\":\"cd\"}" |> Decode.fromBytes Json.fromUtf8 is
-                    Ok { first, second } -> Str.concat first second
+                    Ok {first: "ab", second: "cd"} -> "abcd"
                     _ -> "something went wrong"
             "#
         ),
-        RocStr::from("ab  "),
+        RocStr::from("abcd"),
         RocStr
     )
 }