[ruby/yarp] Check whether the conditional predicate is closed

https://github.com/ruby/yarp/commit/5022b51db2

test/yarp/errors_test.rb

@@ -1302,6 +1302,14 @@ module YARP
       assert_error_messages "%sXfooX", error_messages
     end
 
+    def test_conditional_predicate_closed
+      source = "if 0 0; end\nunless 0 0; end"
+      assert_errors expression(source), source, [
+        ["Expected `then` or `;` or '\n" + "'", 5..6],
+        ["Expected `then` or `;` or '\n" + "'", 21..22],
+      ]
+    end
+
     private
 
     def assert_errors(expected, source, errors, compare_ripper: RUBY_ENGINE == "ruby")

yarp/diagnostic.c

@@ -93,6 +93,7 @@ static const char* const diagnostic_messages[YP_DIAGNOSTIC_ID_LEN] = {
     [YP_ERR_CLASS_TERM]                         = "Expected an `end` to close the `class` statement",
     [YP_ERR_CONDITIONAL_ELSIF_PREDICATE]        = "Expected a predicate expression for the `elsif` statement",
     [YP_ERR_CONDITIONAL_IF_PREDICATE]           = "Expected a predicate expression for the `if` statement",
+    [YP_ERR_CONDITIONAL_PREDICATE_TERM]         = "Expected `then` or `;` or '\n'",
     [YP_ERR_CONDITIONAL_TERM]                   = "Expected an `end` to close the conditional clause",
     [YP_ERR_CONDITIONAL_TERM_ELSE]              = "Expected an `end` to close the `else` clause",
     [YP_ERR_CONDITIONAL_UNLESS_PREDICATE]       = "Expected a predicate expression for the `unless` statement",

yarp/diagnostic.h

@@ -58,6 +58,7 @@ typedef enum {
     YP_ERR_CLASS_TERM,
     YP_ERR_CONDITIONAL_ELSIF_PREDICATE,
     YP_ERR_CONDITIONAL_IF_PREDICATE,
+    YP_ERR_CONDITIONAL_PREDICATE_TERM,
     YP_ERR_CONDITIONAL_TERM,
     YP_ERR_CONDITIONAL_TERM_ELSE,
     YP_ERR_CONDITIONAL_UNLESS_PREDICATE,

yarp/yarp.c

@@ -9814,8 +9814,11 @@ parse_conditional(yp_parser_t *parser, yp_context_t context) {
     yp_node_t *predicate = parse_expression(parser, YP_BINDING_POWER_MODIFIER, error_id);
 
     // Predicates are closed by a term, a "then", or a term and then a "then".
-    accept2(parser, YP_TOKEN_NEWLINE, YP_TOKEN_SEMICOLON);
+    bool predicate_closed = accept2(parser, YP_TOKEN_NEWLINE, YP_TOKEN_SEMICOLON);
-    accept1(parser, YP_TOKEN_KEYWORD_THEN);
+    predicate_closed |= accept1(parser, YP_TOKEN_KEYWORD_THEN);
+    if (!predicate_closed) {
+        yp_diagnostic_list_append(&parser->error_list, parser->current.start, parser->current.end, YP_ERR_CONDITIONAL_PREDICATE_TERM);
+    }
 
     context_pop(parser);
     yp_statements_node_t *statements = NULL;