Reject endless method as a block parameter default

config.yml

@@ -280,6 +280,7 @@ errors:
   - UNEXPECTED_INDEX_KEYWORDS
   - UNEXPECTED_LABEL
   - UNEXPECTED_MULTI_WRITE
+  - UNEXPECTED_PARAMETER_DEFAULT_VALUE
   - UNEXPECTED_RANGE_OPERATOR
   - UNEXPECTED_SAFE_NAVIGATION
   - UNEXPECTED_TOKEN_CLOSE_CONTEXT
@@ -356,6 +357,8 @@ tokens:
     comment: "a newline character outside of other tokens"
   - name: PARENTHESIS_RIGHT
     comment: ")"
+  - name: PIPE
+    comment: "|"
   - name: SEMICOLON
     comment: ";"
   # Tokens from here on are not used for lookup, and can be in any order.
@@ -589,8 +592,6 @@ tokens:
     comment: "%I"
   - name: PERCENT_UPPER_W
     comment: "%W"
-  - name: PIPE
-    comment: "|"
   - name: PIPE_EQUAL
     comment: "|="
   - name: PIPE_PIPE

include/prism/parser.h

@@ -299,6 +299,9 @@ typedef enum {
     /** a rescue else statement within a do..end block */
     PM_CONTEXT_BLOCK_ELSE,
 
+    /** expressions in block parameters `foo do |...| end ` */
+    PM_CONTEXT_BLOCK_PARAMETERS,
+
     /** a rescue statement within a do..end block */
     PM_CONTEXT_BLOCK_RESCUE,
 

src/prism.c

@@ -8606,6 +8606,7 @@ static const uint32_t context_terminators[] = {
     [PM_CONTEXT_BLOCK_KEYWORDS] = (1U << PM_TOKEN_KEYWORD_END) | (1U << PM_TOKEN_KEYWORD_RESCUE) | (1U << PM_TOKEN_KEYWORD_ENSURE),
     [PM_CONTEXT_BLOCK_ENSURE] = (1U << PM_TOKEN_KEYWORD_END),
     [PM_CONTEXT_BLOCK_ELSE] = (1U << PM_TOKEN_KEYWORD_ENSURE) | (1U << PM_TOKEN_KEYWORD_END),
+    [PM_CONTEXT_BLOCK_PARAMETERS] = (1U << PM_TOKEN_PIPE),
     [PM_CONTEXT_BLOCK_RESCUE] = (1U << PM_TOKEN_KEYWORD_ENSURE) | (1U << PM_TOKEN_KEYWORD_RESCUE) | (1U << PM_TOKEN_KEYWORD_ELSE) | (1U << PM_TOKEN_KEYWORD_END),
     [PM_CONTEXT_CASE_WHEN] = (1U << PM_TOKEN_KEYWORD_WHEN) | (1U << PM_TOKEN_KEYWORD_END) | (1U << PM_TOKEN_KEYWORD_ELSE),
     [PM_CONTEXT_CASE_IN] = (1U << PM_TOKEN_KEYWORD_IN) | (1U << PM_TOKEN_KEYWORD_END) | (1U << PM_TOKEN_KEYWORD_ELSE),
@@ -8756,6 +8757,7 @@ context_human(pm_context_t context) {
         case PM_CONTEXT_BEGIN: return "begin statement";
         case PM_CONTEXT_BLOCK_BRACES: return "'{'..'}' block";
         case PM_CONTEXT_BLOCK_KEYWORDS: return "'do'..'end' block";
+        case PM_CONTEXT_BLOCK_PARAMETERS: return "'|'..'|' block parameter";
         case PM_CONTEXT_CASE_WHEN: return "'when' clause";
         case PM_CONTEXT_CASE_IN: return "'in' clause";
         case PM_CONTEXT_CLASS: return "class definition";
@@ -15357,6 +15359,9 @@ parse_block_parameters(
 ) {
     pm_parameters_node_t *parameters = NULL;
     if (!match1(parser, PM_TOKEN_SEMICOLON)) {
+        if (!is_lambda_literal) {
+            context_push(parser, PM_CONTEXT_BLOCK_PARAMETERS);
+        }
         parameters = parse_parameters(
             parser,
             is_lambda_literal ? PM_BINDING_POWER_DEFINED : PM_BINDING_POWER_INDEX,
@@ -15367,6 +15372,9 @@ parse_block_parameters(
             true,
             (uint16_t) (depth + 1)
         );
+        if (!is_lambda_literal) {
+            context_pop(parser);
+        }
     }
 
     pm_block_parameters_node_t *block_parameters = pm_block_parameters_node_create(parser, parameters, opening);
@@ -15722,6 +15730,7 @@ parse_return(pm_parser_t *parser, pm_node_t *node) {
             case PM_CONTEXT_BLOCK_ENSURE:
             case PM_CONTEXT_BLOCK_KEYWORDS:
             case PM_CONTEXT_BLOCK_RESCUE:
+            case PM_CONTEXT_BLOCK_PARAMETERS:
             case PM_CONTEXT_DEF_ELSE:
             case PM_CONTEXT_DEF_ENSURE:
             case PM_CONTEXT_DEF_PARAMS:
@@ -15758,6 +15767,7 @@ parse_block_exit(pm_parser_t *parser, pm_node_t *node) {
             case PM_CONTEXT_BLOCK_KEYWORDS:
             case PM_CONTEXT_BLOCK_ELSE:
             case PM_CONTEXT_BLOCK_ENSURE:
+            case PM_CONTEXT_BLOCK_PARAMETERS:
             case PM_CONTEXT_BLOCK_RESCUE:
             case PM_CONTEXT_DEFINED:
             case PM_CONTEXT_FOR:
@@ -17975,6 +17985,7 @@ parse_retry(pm_parser_t *parser, const pm_node_t *node) {
             case PM_CONTEXT_BEGIN:
             case PM_CONTEXT_BLOCK_BRACES:
             case PM_CONTEXT_BLOCK_KEYWORDS:
+            case PM_CONTEXT_BLOCK_PARAMETERS:
             case PM_CONTEXT_CASE_IN:
             case PM_CONTEXT_CASE_WHEN:
             case PM_CONTEXT_DEFAULT_PARAMS:
@@ -18055,6 +18066,7 @@ parse_yield(pm_parser_t *parser, const pm_node_t *node) {
             case PM_CONTEXT_BLOCK_KEYWORDS:
             case PM_CONTEXT_BLOCK_ELSE:
             case PM_CONTEXT_BLOCK_ENSURE:
+            case PM_CONTEXT_BLOCK_PARAMETERS:
             case PM_CONTEXT_BLOCK_RESCUE:
             case PM_CONTEXT_CASE_IN:
             case PM_CONTEXT_CASE_WHEN:
@@ -19618,6 +19630,12 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
                 if (!accept_endless_def) {
                     pm_parser_err_previous(parser, PM_ERR_DEF_ENDLESS_PARAMETERS);
                 }
+                if (
+                    parser->current_context->context == PM_CONTEXT_DEFAULT_PARAMS &&
+                    parser->current_context->prev->context == PM_CONTEXT_BLOCK_PARAMETERS
+                ) {
+                    PM_PARSER_ERR_FORMAT(parser, def_keyword.start, parser->previous.end, PM_ERR_UNEXPECTED_PARAMETER_DEFAULT_VALUE, "endless method definition");
+                }
                 equal = parser->previous;
 
                 context_push(parser, PM_CONTEXT_DEF);

templates/src/diagnostic.c.erb

@@ -361,6 +361,7 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_ERR_UNEXPECTED_INDEX_KEYWORDS]          = { "unexpected keyword arg given in index assignment; keywords are not allowed in index assignment expressions", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_LABEL]                   = { "unexpected label", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_MULTI_WRITE]             = { "unexpected multiple assignment; multiple assignment is not allowed in this context", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_UNEXPECTED_PARAMETER_DEFAULT_VALUE] = { "unexpected %s; expected a default value for a parameter", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_RANGE_OPERATOR]          = { "unexpected range operator; .. and ... are non-associative and cannot be chained", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_SAFE_NAVIGATION]         = { "&. inside multiple assignment destination", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_TOKEN_CLOSE_CONTEXT]     = { "unexpected %s, assuming it is closing the parent %s", PM_ERROR_LEVEL_SYNTAX },

test/prism/errors/block_args_with_endless_def.txt

@@ -0,0 +1,5 @@
+p do |a = def f = 1; b| end
+          ^~~~~~~ unexpected endless method definition; expected a default value for a parameter
+p do |a = def f = 1| 2; b|c end
+          ^~~~~~~ unexpected endless method definition; expected a default value for a parameter
+

test/prism/fixtures/endless_method_as_default_arg.txt

@@ -0,0 +1,11 @@
+def foo(a = def f = 1); end
+
+def foo(a = def f = 1, b); end
+
+def foo(b, a = def f = 1); end
+
+def foo(a: def f = 1); end
+
+def foo(a = def f = 1+2); end
+
+->(a = def f = 1) {}