Prevent optional block parameter from accepting certain prefixed values

This commit prevents the following unary operators from being accepted
as the value prefix of a block's optional parameter:

- `+`
- `-`
- `~`
- `!`

For example, `f { |a = +b| }` will now raise a syntax error.

Co-authored-by: Kevin Newton <[email protected]>

Author: st0012

config.yml

@@ -261,6 +261,7 @@ errors:
   - TERNARY_COLON
   - TERNARY_EXPRESSION_FALSE
   - TERNARY_EXPRESSION_TRUE
+  - UNARY_DISALLOWED
   - UNARY_RECEIVER
   - UNDEF_ARGUMENT
   - UNEXPECTED_BLOCK_ARGUMENT

src/prism.c

@@ -17142,6 +17142,10 @@ pm_parser_err_prefix(pm_parser_t *parser, pm_diagnostic_id_t diag_id) {
             PM_PARSER_ERR_TOKEN_FORMAT(parser, parser->previous, diag_id, human, parser->previous.start[0]);
             break;
         }
+        case PM_ERR_UNARY_DISALLOWED: {
+            PM_PARSER_ERR_TOKEN_FORMAT(parser, parser->current, diag_id, pm_token_type_human(parser->current.type));
+            break;
+        }
         default:
             pm_parser_err_previous(parser, diag_id);
             break;
@@ -19675,6 +19679,10 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
             }
         }
         case PM_TOKEN_BANG: {
+            if (binding_power > PM_BINDING_POWER_UNARY) {
+                pm_parser_err_prefix(parser, PM_ERR_UNARY_DISALLOWED);
+            }
+
             parser_lex(parser);
 
             pm_token_t operator = parser->previous;
@@ -19685,6 +19693,9 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
             return (pm_node_t *) node;
         }
         case PM_TOKEN_TILDE: {
+            if (binding_power > PM_BINDING_POWER_UNARY) {
+                pm_parser_err_prefix(parser, PM_ERR_UNARY_DISALLOWED);
+            }
             parser_lex(parser);
 
             pm_token_t operator = parser->previous;
@@ -19694,6 +19705,9 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
             return (pm_node_t *) node;
         }
         case PM_TOKEN_UMINUS: {
+            if (binding_power > PM_BINDING_POWER_UNARY) {
+                pm_parser_err_prefix(parser, PM_ERR_UNARY_DISALLOWED);
+            }
             parser_lex(parser);
 
             pm_token_t operator = parser->previous;
@@ -19810,6 +19824,9 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
             return (pm_node_t *) pm_lambda_node_create(parser, &locals, &operator, &opening, &parser->previous, parameters, body);
         }
         case PM_TOKEN_UPLUS: {
+            if (binding_power > PM_BINDING_POWER_UNARY) {
+                pm_parser_err_prefix(parser, PM_ERR_UNARY_DISALLOWED);
+            }
             parser_lex(parser);
 
             pm_token_t operator = parser->previous;

templates/src/diagnostic.c.erb

@@ -344,6 +344,7 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_ERR_TERNARY_EXPRESSION_TRUE]            = { "expected an expression after `?` in the ternary operator", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNDEF_ARGUMENT]                     = { "invalid argument being passed to `undef`; expected a bare word, constant, or symbol argument", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNARY_RECEIVER]                     = { "unexpected %s, expected a receiver for unary `%c`", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_UNARY_DISALLOWED]                   = { "unexpected %s; unary calls are not allowed in this context", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_BLOCK_ARGUMENT]          = { "block argument should not be given", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_INDEX_BLOCK]             = { "unexpected block arg given in index assignment; blocks are not allowed in index assignment expressions", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_INDEX_KEYWORDS]          = { "unexpected keyword arg given in index assignment; keywords are not allowed in index assignment expressions", PM_ERROR_LEVEL_SYNTAX },

test/prism/errors_test.rb

@@ -1493,6 +1493,17 @@ def test_shadow_args_in_block
       ]
     end
 
+    def test_optional_block_parameters_with_unary_operator
+      [
+        ["foo { |a = +b| }", ["unexpected '+'; unary calls are not allowed in this context", 11..12]],
+        ["foo { |a = -b| }", ["unexpected '-'; unary calls are not allowed in this context", 11..12]],
+        ["foo { |a = !b| }", ["unexpected '!'; unary calls are not allowed in this context", 11..12]],
+        ["foo { |a = ~b| }", ["unexpected '~'; unary calls are not allowed in this context", 11..12]],
+      ].each do |source, *errors|
+        assert_errors expression(source), source, errors
+      end
+    end
+
     def test_repeated_parameter_name_in_destructured_params
       source = "def f(a, (b, (a))); end"