[ruby/prism] Check circular references in default values of params

Fix https://github.com/ruby/prism/pull/1637

https://github.com/ruby/prism/commit/0172d69cba

4 files changed, 43 insertions, 1 deletions

diff --git a/prism/diagnostic.h b/prism/diagnostic.h
index 06d90ec026..3614a38ae7 100644
--- a/prism/diagnostic.h
+++ b/prism/diagnostic.h
@@ -192,6 +192,7 @@ typedef enum {
     PM_ERR_OPERATOR_WRITE_BLOCK,
     PM_ERR_PARAMETER_ASSOC_SPLAT_MULTI,
     PM_ERR_PARAMETER_BLOCK_MULTI,
+    PM_ERR_PARAMETER_CIRCULAR,
     PM_ERR_PARAMETER_METHOD_NAME,
     PM_ERR_PARAMETER_NAME_REPEAT,
     PM_ERR_PARAMETER_NO_DEFAULT,
diff --git a/prism/parser.h b/prism/parser.h
index 86442d2a22..89963ab08a 100644
--- a/prism/parser.h
+++ b/prism/parser.h
@@ -676,6 +676,13 @@ struct pm_parser {
     bool in_keyword_arg;
 
     /**
+     * The current parameter name id on parsing its default value.
+     * Since this is used for detecting circular references, this is available
+     * only on `PM_CONTEXT_DEFAULT_PARAM`.
+     */
+    pm_constant_id_t current_param_name;
+
+    /**
      * Whether or not the parser has seen a token that has semantic meaning
      * (i.e., a token that is not a comment or whitespace).
      */
diff --git a/prism/prism.c b/prism/prism.c
index 1720d9089d..d0cfbef41d 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -4040,11 +4040,22 @@ pm_local_variable_or_write_node_create(pm_parser_t *parser, pm_node_t *target, c
     return node;
 }
 
+static bool context_p(pm_parser_t *parser, pm_context_t context);
+
 /**
  * Allocate a new LocalVariableReadNode node.
  */
 static pm_local_variable_read_node_t *
 pm_local_variable_read_node_create(pm_parser_t *parser, const pm_token_t *name, uint32_t depth) {
+    pm_constant_id_t name_id = pm_parser_constant_id_token(parser, name);
+
+    if (
+        context_p(parser, PM_CONTEXT_DEFAULT_PARAMS) &&
+        parser->current_param_name == name_id
+    ) {
+        pm_parser_err_token(parser, name, PM_ERR_PARAMETER_CIRCULAR);
+    }
+
     pm_local_variable_read_node_t *node = PM_ALLOC_NODE(parser, pm_local_variable_read_node_t);
 
     *node = (pm_local_variable_read_node_t) {
@@ -4052,7 +4063,7 @@ pm_local_variable_read_node_create(pm_parser_t *parser, const pm_token_t *name,
             .type = PM_LOCAL_VARIABLE_READ_NODE,
             .location = PM_LOCATION_TOKEN_VALUE(name)
         },
-        .name = pm_parser_constant_id_token(parser, name),
+        .name = name_id,
         .depth = depth
     };
 
@@ -11596,10 +11607,14 @@ parse_parameters(
                 if (accept1(parser, PM_TOKEN_EQUAL)) {
                     pm_token_t operator = parser->previous;
                     context_push(parser, PM_CONTEXT_DEFAULT_PARAMS);
+                    pm_constant_id_t old_param_name = parser->current_param_name;
+                    parser->current_param_name = pm_parser_constant_id_token(parser, &name);
                     pm_node_t *value = parse_value_expression(parser, binding_power, PM_ERR_PARAMETER_NO_DEFAULT);
 
                     pm_optional_parameter_node_t *param = pm_optional_parameter_node_create(parser, &name, &operator, value);
                     pm_parameters_node_optionals_append(params, param);
+
+                    parser->current_param_name = old_param_name;
                     context_pop(parser);
 
                     // If parsing the value of the parameter resulted in error recovery,
@@ -11655,7 +11670,10 @@ parse_parameters(
 
                         if (token_begins_expression_p(parser->current.type)) {
                             context_push(parser, PM_CONTEXT_DEFAULT_PARAMS);
+                            pm_constant_id_t old_param_name = parser->current_param_name;
+                            parser->current_param_name = pm_parser_constant_id_token(parser, &local);
                             pm_node_t *value = parse_value_expression(parser, binding_power, PM_ERR_PARAMETER_NO_DEFAULT_KW);
+                            parser->current_param_name = old_param_name;
                             context_pop(parser);
                             param = (pm_node_t *) pm_optional_keyword_parameter_node_create(parser, &name, value);
                         }
diff --git a/test/prism/errors_test.rb b/test/prism/errors_test.rb
index bcc9629622..9c96725463 100644
--- a/test/prism/errors_test.rb
+++ b/test/prism/errors_test.rb
@@ -1829,6 +1829,22 @@ module Prism
       ]
     end
 
+    def test_circular_param
+      source = <<~RUBY
+        def foo(bar = bar) = 42
+        def foo(bar: bar) = 42
+        proc { |foo = foo| }
+        proc { |foo: foo| }
+      RUBY
+      message = 'Invalid circular reference in a default parameter'
+      assert_errors expression(source), source, [
+        [message, 14..17],
+        [message, 37..40],
+        [message, 61..64],
+        [message, 81..84],
+      ], compare_ripper: false # Ripper does not check 'circular reference'.
+    end
+
     private
 
     def assert_errors(expected, source, errors, compare_ripper: RUBY_ENGINE == "ruby")