[ruby/yarp] Handle missing clauses in case statement

https://github.com/ruby/yarp/commit/1ad7fba5ef

test/yarp/errors_test.rb

@@ -949,7 +949,21 @@ module YARP
       )
 
       assert_errors expected, "case :a\nelse\nend", [
-        ["Unexpected `else` in `case` statement; a `when` clause must precede `else`", 8..12]
+        ["Expected a `when` or `in` clause after `case`", 0..4]
+      ]
+    end
+
+    def test_case_without_clauses
+      expected = CaseNode(
+        SymbolNode(Location(), Location(), nil, "a"),
+        [],
+        nil,
+        Location(),
+        Location()
+      )
+
+      assert_errors expected, "case :a\nend", [
+        ["Expected a `when` or `in` clause after `case`", 0..4]
       ]
     end
 

yarp/diagnostic.c

@@ -85,7 +85,7 @@ static const char* const diagnostic_messages[YP_DIAGNOSTIC_ID_LEN] = {
     [YP_ERR_CANNOT_PARSE_STRING_PART]           = "Cannot parse the string part",
     [YP_ERR_CASE_EXPRESSION_AFTER_CASE]         = "Expected an expression after `case`",
     [YP_ERR_CASE_EXPRESSION_AFTER_WHEN]         = "Expected an expression after `when`",
-    [YP_ERR_CASE_LONELY_ELSE]                   = "Unexpected `else` in `case` statement; a `when` clause must precede `else`",
+    [YP_ERR_CASE_MISSING_CONDITIONS]            = "Expected a `when` or `in` clause after `case`",
     [YP_ERR_CASE_TERM]                          = "Expected an `end` to close the `case` statement",
     [YP_ERR_CLASS_IN_METHOD]                    = "Unexpected class definition in a method body",
     [YP_ERR_CLASS_NAME]                         = "Expected a constant name after `class`",

yarp/diagnostic.h

@@ -50,7 +50,7 @@ typedef enum {
     YP_ERR_CANNOT_PARSE_STRING_PART,
     YP_ERR_CASE_EXPRESSION_AFTER_CASE,
     YP_ERR_CASE_EXPRESSION_AFTER_WHEN,
-    YP_ERR_CASE_LONELY_ELSE,
+    YP_ERR_CASE_MISSING_CONDITIONS,
     YP_ERR_CASE_TERM,
     YP_ERR_CLASS_IN_METHOD,
     YP_ERR_CLASS_NAME,

yarp/yarp.c

@@ -11935,6 +11935,7 @@ parse_expression_prefix(yp_parser_t *parser, yp_binding_power_t binding_power) {
             }
 
             if (accept1(parser, YP_TOKEN_KEYWORD_END)) {
+                yp_diagnostic_list_append(&parser->error_list, case_keyword.start, case_keyword.end, YP_ERR_CASE_MISSING_CONDITIONS);
                 return (yp_node_t *) yp_case_node_create(parser, &case_keyword, predicate, NULL, &parser->previous);
             }
 
@@ -12041,12 +12042,14 @@ parse_expression_prefix(yp_parser_t *parser, yp_binding_power_t binding_power) {
                 }
             }
 
+            // If we didn't parse any conditions (in or when) then we need to
+            // indicate that we have an error.
+            if (case_node->conditions.size == 0) {
+                yp_diagnostic_list_append(&parser->error_list, case_keyword.start, case_keyword.end, YP_ERR_CASE_MISSING_CONDITIONS);
+            }
+
             accept2(parser, YP_TOKEN_NEWLINE, YP_TOKEN_SEMICOLON);
             if (accept1(parser, YP_TOKEN_KEYWORD_ELSE)) {
-                if (case_node->conditions.size < 1) {
-                    yp_diagnostic_list_append(&parser->error_list, parser->previous.start, parser->previous.end, YP_ERR_CASE_LONELY_ELSE);
-                }
-
                 yp_token_t else_keyword = parser->previous;
                 yp_else_node_t *else_node;