[fine] Working on parser resilience

fine/src/parser.rs

@@ -395,6 +395,15 @@ impl<'a> CParser<'a> {
     //     eprintln!("{}: {}: {}", self.current.start, self.current, msg);
     // }
 
+    fn at_any(&self, kinds: &[TokenKind]) -> bool {
+        for kind in kinds {
+            if self.at(*kind) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     fn at(&self, kind: TokenKind) -> bool {
         self.peek() == kind
     }
@@ -586,6 +595,8 @@ fn field_decl(p: &mut CParser) {
     p.end(m, TreeKind::FieldDecl);
 }
 
+const PARAM_LIST_RECOVERY: &[TokenKind] = &[TokenKind::Arrow, TokenKind::LeftBrace, TokenKind::Fun];
+
 fn param_list(p: &mut CParser) {
     let m = p.start();
 
@@ -594,7 +605,10 @@ fn param_list(p: &mut CParser) {
         if p.at(TokenKind::Identifier) {
             parameter(p);
         } else {
-            break;
+            if p.at_any(PARAM_LIST_RECOVERY) {
+                break;
+            }
+            p.advance_with_error("expected parameter");
         }
     }
     p.expect(TokenKind::RightParen, "expect ')' to end a parameter list");