Merge pull request #605 from HigherOrderCO/468-patterns-in-fun-rules-shouldnt-accept-unscoped-variables

#468 Patterns in "fun" rules should accept unscoped variables

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project does not currently adhere to a particular versioning scheme.
 
 - Fix readback of numeric operations. ([#467][gh-467])
 - Propagate the "builtin" attribute of definitions when extracting functions from `bend` and `fold` syntax.
+- Panic while using unscoped variables on definition patterns. ([#468][gh-468])
 
 ### Added
 
@@ -339,6 +340,7 @@ and this project does not currently adhere to a particular versioning scheme.
 [gh-465]: https://github.com/HigherOrderCO/Bend/issues/465
 [gh-466]: https://github.com/HigherOrderCO/Bend/issues/466
 [gh-467]: https://github.com/HigherOrderCO/Bend/issues/467
+[gh-468]: https://github.com/HigherOrderCO/Bend/issues/468
 [gh-470]: https://github.com/HigherOrderCO/Bend/issues/470
 [gh-475]: https://github.com/HigherOrderCO/Bend/issues/475
 [gh-478]: https://github.com/HigherOrderCO/Bend/issues/478

src/fun/transform/desugar_match_defs.rs

@@ -127,9 +127,19 @@ fn simplify_rule_match(
 fn irrefutable_fst_row_rule(args: Vec<Name>, rule: Rule) -> Term {
   let mut term = rule.body;
   for (arg, pat) in args.into_iter().zip(rule.pats.into_iter()) {
-    let Pattern::Var(var) = pat else { unreachable!() };
-    if let Some(var) = var {
-      term = Term::Use { nam: Some(var), val: Box::new(Term::Var { nam: arg }), nxt: Box::new(term) };
+    match pat {
+      Pattern::Var(None) => {}
+      Pattern::Var(Some(var)) => {
+        term = Term::Use { nam: Some(var), val: Box::new(Term::Var { nam: arg }), nxt: Box::new(term) };
+      }
+      Pattern::Chn(var) => {
+        term = Term::Let {
+          pat: Box::new(Pattern::Chn(var)),
+          val: Box::new(Term::Var { nam: arg }),
+          nxt: Box::new(term),
+        };
+      }
+      _ => unreachable!(),
     }
   }
   term

tests/golden_tests/compile_file/def_pat_unscoped.bend

@@ -0,0 +1,3 @@
+add $a b = (+ $a b)
+
+main = (add 9 4)

tests/snapshots/compile_file__def_pat_unscoped.bend.snap

@@ -0,0 +1,8 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/compile_file/def_pat_unscoped.bend
+---
+@add = ($([+] $(a b)) (a b))
+
+@main = a
+  & @add ~ (9 (4 a))