Support bare : as keyword for true

snapshots/booleans.txt

@@ -1,11 +1,13 @@
-@ ProgramNode (location: (1,0)-(3,4))
+@ ProgramNode (location: (1,0)-(5,1))
 ├── flags: ∅
 ├── locals: []
 └── statements:
-    @ StatementsNode (location: (1,0)-(3,4))
+    @ StatementsNode (location: (1,0)-(5,1))
     ├── flags: ∅
-    └── body: (length: 2)
+    └── body: (length: 3)
         ├── @ FalseNode (location: (1,0)-(1,5))
         │   └── flags: newline, static_literal
-        └── @ TrueNode (location: (3,0)-(3,4))
+        ├── @ TrueNode (location: (3,0)-(3,4))
+        │   └── flags: newline, static_literal
+        └── @ TrueNode (location: (5,0)-(5,1))
             └── flags: newline, static_literal

src/prism.c

@@ -6889,7 +6889,7 @@ pm_symbol_node_to_string_node(pm_parser_t *parser, pm_symbol_node_t *node) {
  */
 static pm_true_node_t *
 pm_true_node_create(pm_parser_t *parser, const pm_token_t *token) {
-    assert(token->type == PM_TOKEN_KEYWORD_TRUE);
+    assert(token->type == PM_TOKEN_KEYWORD_TRUE || token->type == PM_TOKEN_COLON);
 
     return pm_true_node_new(
         parser->arena,
@@ -11009,7 +11009,7 @@ parser_lex(pm_parser_t *parser) {
                         LEX(PM_TOKEN_COLON_COLON);
                     }
 
-                    if (lex_state_end_p(parser) || pm_char_is_whitespace(peek(parser)) || peek(parser) == '#') {
+                    if (lex_state_end_p(parser) || pm_char_is_whitespace(peek(parser)) || peek(parser) == '#' || peek(parser) == '\0') {
                         lex_state_set(parser, PM_LEX_STATE_BEG);
                         LEX(PM_TOKEN_COLON);
                     }
@@ -19989,6 +19989,7 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, u
         case PM_TOKEN_KEYWORD_SELF:
             parser_lex(parser);
             return UP(pm_self_node_create(parser, &parser->previous));
+        case PM_TOKEN_COLON:
         case PM_TOKEN_KEYWORD_TRUE:
             parser_lex(parser);
             return UP(pm_true_node_create(parser, &parser->previous));

test/prism/fixtures/booleans.txt

@@ -1,3 +1,5 @@
 false
 
 true
+
+:

test/prism/ruby/parser_test.rb

@@ -68,6 +68,9 @@ class ParserTest < TestCase
 
       # https://bugs.ruby-lang.org/issues/21168#note-5
       "command_method_call_2.txt",
+
+      # Contains standalone `:` keyword (not supported by parser gem).
+      "booleans.txt",
     ]
 
     # These files contain code that is being parsed incorrectly by the parser

test/prism/ruby/ripper_test.rb

@@ -44,6 +44,9 @@ class RipperTest < TestCase
       ]
     end
 
+    # CRuby doesn't support standalone `:` as a keyword (equivalent to `true`).
+    incorrect << "booleans.txt"
+
     # https://bugs.ruby-lang.org/issues/21669
     incorrect << "4.1/void_value.txt"
     # https://bugs.ruby-lang.org/issues/19107

test/prism/ruby/ruby_parser_test.rb

@@ -88,6 +88,9 @@ class RubyParserTest < TestCase
 
       # https://bugs.ruby-lang.org/issues/21168#note-5
       "command_method_call_2.txt",
+
+      # Contains standalone `:` keyword (not supported by ruby_parser).
+      "booleans.txt",
     ]
 
     Fixture.each_for_version(version: "3.3", except: failures) do |fixture|