Add required array element constraints

crates/decodal-core/src/lexer.rs

@@ -32,6 +32,7 @@ pub enum TokenKind {
     Semicolon,
     Comma,
     Dot,
+    Ellipsis,
     Colon,
     Equal,
     EqualEqual,
@@ -141,7 +142,18 @@ impl<'a> Lexer<'a> {
             }
             b'.' => {
                 self.pos += 1;
-                TokenKind::Dot
+                if self.consume(b'.') {
+                    if self.consume(b'.') {
+                        TokenKind::Ellipsis
+                    } else {
+                        return Err(Diagnostic::syntax(
+                            self.span(start, self.pos),
+                            "expected third '.' in ellipsis",
+                        ));
+                    }
+                } else {
+                    TokenKind::Dot
+                }
             }
             b':' => {
                 self.pos += 1;
@@ -432,4 +444,13 @@ mod tests {
         assert_eq!(tokens[3].kind, TokenKind::Amp);
         assert_eq!(tokens[4].kind, TokenKind::Gte);
     }
+
+    #[test]
+    fn tokenizes_array_constraint_ellipsis() {
+        let tokens = Lexer::new("[...String]").tokenize().unwrap();
+        assert_eq!(tokens[0].kind, TokenKind::LBracket);
+        assert_eq!(tokens[1].kind, TokenKind::Ellipsis);
+        assert!(matches!(tokens[2].kind, TokenKind::Ident(_)));
+        assert_eq!(tokens[3].kind, TokenKind::RBracket);
+    }
 }