Add missing error message

src/fun/parser.rs

@@ -495,27 +495,26 @@ impl<'a> TermParser<'a> {
         self.skip_trivia();
         let (cur_name, rule) = self.parse_rule()?;
         let mut rules = vec![rule];
-        let mut cur_idx = *self.index();
+        let mut nxt_term = *self.index();
         loop {
           self.skip_trivia();
-          let back_term = *self.index();
+          let nxt_def = *self.index();
           match self.parse_rule() {
             Ok((name, rule)) => {
               if name == "def" {
-                self.index = back_term;
+                self.index = nxt_def;
                 return Ok(Term::Def { nam: cur_name, rules, nxt: Box::new(self.parse_term()?) });
               }
               if name == cur_name {
                 rules.push(rule);
-                cur_idx = *self.index();
+                nxt_term = *self.index();
               } else {
-                panic!()
+                let cur = *self.index();
+                let msg = format!("Expected a rule with name '{cur_name}'.");
+                return self.with_ctx(Err(msg), nxt_def..cur);
               }
             }
-            Err(_) => {
-              self.index = cur_idx;
-              break;
-            }
+            Err(_) => break self.index = nxt_term,
           }
         }
         let nxt = self.parse_term()?;

src/fun/transform/lift_defs.rs

@@ -77,13 +77,13 @@ fn gen_use(
     fvs.iter().cloned().map(|nam| Term::Var { nam }).collect::<Vec<_>>(),
   );
 
-  let r#use = Term::Use { nam: Some(nam.clone()), val: Box::new(call.clone()), nxt: std::mem::take(nxt) };
-
   for rule in rules.iter_mut() {
     let slf = std::mem::take(&mut rule.body);
     rule.body = Term::Use { nam: Some(nam.clone()), val: Box::new(call.clone()), nxt: Box::new(slf) };
   }
 
+  let r#use = Term::Use { nam: Some(nam.clone()), val: Box::new(call.clone()), nxt: std::mem::take(nxt) };
+
   (r#use, fvs, rules)
 }
 

tests/golden_tests/parse_file/fun_def.bend

@@ -0,0 +1,5 @@
+main =
+  let base = 0
+  def aux [] = base
+      aux (List/Cons head tail) = (+ head (aux tail))
+  (aux [1, 2, 3])

tests/golden_tests/parse_file/fun_def_name.bend

@@ -0,0 +1,5 @@
+main =
+  let base = 0
+  def aux [] = base
+      aux2 (List/Cons head tail) = (+ head (aux tail))
+  (aux [1, 2, 3])

tests/snapshots/parse_file__fun_def.bend.snap

@@ -0,0 +1,5 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/parse_file/fun_def.bend
+---
+(main) = let base = 0; def (aux []) = base(aux (List/Cons head tail)) = (+ head (aux tail))(aux [1, 2, 3])

tests/snapshots/parse_file__fun_def_name.bend.snap

@@ -0,0 +1,8 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/parse_file/fun_def_name.bend
+---
+Errors:
+In tests/golden_tests/parse_file/fun_def_name.bend :
+Expected a rule with name 'aux'.
+  4 |       aux2 (List/Cons head tail) = (+ head (aux tail))